# Gaia DR3: Specific processing and validation of all-sky RR Lyrae and Cepheid stars - The RR Lyrae sample

G. Clementini, V. Ripepi, A. Garofalo, R. Molinaro, T. Muraveva, S. Leccia, L. Rimoldini, B. Holl, G. Jevardat de Fombelle, P. Sartoretti, et al.

► To cite this version:

G. Clementini, V. Ripepi, A. Garofalo, R. Molinaro, T. Muraveva, et al. Gaia DR3: Specific processing and validation of all-sky RR Lyrae and Cepheid stars - The RR Lyrae sample. Astronomy and Astrophysics - A&A, 2023, 674, pp.A18. 10.1051/0004-6361/202243964. hal-03708499

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# Gaia Data Release 3

## Specific processing and validation of all-sky RR Lyrae and Cepheid stars:
The RR Lyrae sample*

G. Clementini<fnref n="1" />,*, V. Ripepi<fnref n="2" />, A. Garofalo<fnref n="1" />, R. Molinaro<fnref n="2" />, T. Muraveva<fnref n="1" />, S. Leccia<fnref n="2" />, L. Rimoldini<fnref n="3" />,
B. Holl<fnref n="3" />, G. Jevardat de Fombelle<fnref n="3" />, P. Sartoretti<fnref n="4" />, O. Marchal<fnref n="5" />, M. Audard<fnref n="3" />,<fnref n="6" />, K. Nienartowicz<fnref n="3" />,<fnref n="7" />,
R. Andrae<fnref n="8" />, M. Marconi<fnref n="2" />, L. Szabados<fnref n="9" />,<fnref n="10" />, D. W. Evans<fnref n="11" />, I. Lecoeur-Taibi<fnref n="3" />, N. Mowlavi<fnref n="3" />,
I. Musella<fnref n="2" />, and L. Eyer<fnref n="6" />

Received 5 May 2022 / Accepted 4 July 2022

## ABSTRACT

**Context.** RR Lyrae stars are excellent tracers of the oldest stars (ages $\ge$ 9–10 Gyr) and standard candles for measuring the distance to stellar systems that are mainly composed of an old stellar population. The Gaia Third Data Release (DR3) publishes a catalogue of full-sky RR Lyrae stars observed during the initial 34 months of science operations. They were processed through the Specific Object Study (SOS) pipeline, which was developed to validate and characterise Cepheids and RR Lyrae stars (SOS Cep&RRL) observed by Gaia.

**Aims.** The main steps of the SOS Cep&RRL pipeline are described in the documentation and papers accompanying previous Gaia data releases. For DR3, the pipeline was modified in its process: in addition to the Gaia multiband ($G, G_{BP}, G_{RP}$) time-series photometry, the epoch radial velocities measured for RR Lyrae and Cepheids with the Radial Velocity Spectrometer (RVS) on board Gaia were also processed through the pipeline.

**Methods.** The SOS Cep&RRL validation of DR3 candidate RR Lyrae stars relies on diagnostics tools that include the period versus $G$-amplitude diagram and the period versus $\phi_{21}$ and $\phi_{31}$ parameters of the $G$ light-curve Fourier decomposition, as defined by a reference sample of bona fide RR Lyrae stars known in the literature (that we named Gold Sample). Great care was devoted to building a large and pure Gold Sample comprising more than 200 000 RR Lyrae stars. The SOS processing led to an initial catalogue of 271 779 RR Lyrae stars that are listed in the *vari旌lyrae* table of the DR3 archive. A thorough cleaning procedure was then performed to produce a final catalogue of SOS-confirmed DR3 RR Lyrae stars by dropping sources that clearly are contaminants or have an uncertain classification.

**Results.** Multiband time-series photometry and characterisation are published in Gaia DR3 for a clean, validated sample of 270 905 RR Lyrae stars (174 947 fundamental-mode, 93 952 first-overtone, and 2006 double-mode RR Lyrae) that were confirmed and fully characterised by the SOS Cep&RRL pipeline. They are distributed throughout the sky, including variables in 95 globular clusters and 25 Milky Way (MW) companions (the Magellanic Clouds, seven dwarf spheroidal galaxies, and 16 ultra-faint dwarf satellites of the MW). RVS time-series radial velocities are also published for 1096 RR Lyrae and 799 Cepheids of different types (classical, anomalous, and type II Cepheids). Of the 270 905 DR3 RR Lyrae stars, 200 294 are already known in the literature (Gold Sample) and 70 611 are new discoveries by Gaia, to the best of our knowledge. An estimate of the interstellar absorption is published for 142 660 fundamental-mode RR Lyrae stars from a relation based on the $G$-band amplitude, the ($G - G_{RP}$) colour and the pulsation period. Metallicities derived from the Fourier parameters of the light curves are also released for 133 559 RR Lyrae stars.

**Conclusions.** The final Gaia DR3 catalogue of confirmed RR Lyrae stars almost doubles the DR2 RR Lyrae catalogue. An increase in statistical significance, a better characterisation of the RR Lyrae pulsational and astrophysical parameters, and the improved astrometry published with Gaia EDR3 make the SOS Cep&RRL DR3 sample the largest, most homogeneous, and parameter-richest catalogue of all-sky RR Lyrae stars published so far in the magnitude range from $\langle G \rangle = 7.64$ mag (the magnitude of RR Lyr itself, the class prototype) to $\langle G \rangle = 21.14$ mag (the faintest RR Lyrae in the catalogue).

**Key words.** stars: general – stars: oscillations – stars: variables: RR Lyrae – stars: variables: Cepheids – Magellanic Clouds – methods: data analysis

<footnote n="1">¹ INAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, 40129 Bologna, Italy</footnote>

<footnote n="2">² INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Naples, Italy</footnote>

<footnote n="3">³ Department of Astronomy, University of Geneva, Ch. d'Ecogia 16, 1290 Versoix, Switzerland</footnote>

<footnote n="4">⁴ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 place Jules Janssen, 92190 Meudon, France</footnote>

<footnote n="5">⁵ Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l'Université, 67000 Strasbourg, France</footnote>

<footnote n="6">⁶ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland</footnote>

<footnote n="7">⁷ Sednai Sàrl, Geneva, Switzerland</footnote>

<footnote n="8">⁸ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany</footnote>

<footnote n="9">⁹ Konkoly Observatory, ELKH Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary</footnote>

<footnote n="10">¹⁰ CSFK Lendület Near-Field Cosmology Research Group, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary</footnote>

<footnote n="11">¹¹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK</footnote>

<footnote>* Full Tables 2, 5–9, A.1–A.2, and lightcurves are only available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/674/A18</footnote>

<footnote>** Corresponding author: G. Clementini, e-mail: gisella.clementini@inaf.it</footnote>
# 1. Introduction

RR Lyrae are low-mass (typical masses around 0.6–0.8 $M_\odot$), old (ages exceeding 9–10 billion years) stars whose surface expands and contracts regularly with periods shorter than one day. The pulsation gives rise to a variation in brightness that occurs in two main flavours. The light curves of c-type RR Lyrae (RRc) stars are almost sinusoidal. They repeat in time with periodicities of typically between about 0.2 and 0.42 day (d), and an amplitude in light variation of up to about half a magnitude in the visual band. RRc stars oscillate in the radial first-overtone pulsation mode. The ab-type RR Lyrae (RRab) stars have asymmetrical sawtooth light curves, periods of typically between about 0.42 and 1 d, and visual amplitudes in the *Gaia* *G* band from above 0.1 to more than one magnitude. They pulsate in the fundamental pulsation mode. In a small fraction of RR Lyrae stars, fundamental and first-overtone pulsation modes are excited at the same time, giving rise to the double-mode (d-type) RR Lyrae (RRd). The characteristic light variation makes RR Lyrae stars easily recognizable even in very crowded regions of the sky or in high-extinction conditions. Their pulsation characteristics (periods, amplitudes, mean magnitudes and colours, etc.) allow an estimate of their metal abundance and reddening, thus bringing invaluable added values (see e.g. Smith 1995; Catelan & Smith 2015, for comprehensive reviews of RR Lyrae stars).

RR Lyrae stars allow measuring the distance to the systems they live in because they follow luminosity–metallicity (LZ) relations in the visual bands (see e.g. Cacciari & Clementini 2003; Clementini et al. 2003; and references therein and e.g. Muraveva et al. 2018; Garofalo et al. 2022; for more recent LZ relations in the Johnson *V* and *Gaia* *G* bands, calibrated on *Gaia* parallaxes) and period–luminosity–(metallicity) (PLZ) relations in the infrared (see e.g. Muraveva et al. 2018; Bhardwaj et al. 2021, and references therein for PLZ relations in the $K_s$ and $W_1$ infrared bands). These variable stars are the only abundant stellar tracers with a small relative distance error (~5%), particularly at large distances. They therefore allow measuring the most accurate distances to old, distant stellar populations. Moreover, at 5–10 kpc from the Milky Way (MW) disc, they are also the stars with the most precise distances.

RR Lyrae stars are also excellent tracers of the oldest stars that witnessed the first epoch of galaxy formation. They can therefore provide indications about the building blocks that contributed to the build-up of galactic haloes (see e.g. Catelan & Smith 2015; Martínez-Vázquez et al. 2019, and references therein). All these properties make the RR Lyrae stars invaluable dynamical tracers of the Galaxy and a crucial tool for a plethora of applications, from Galactic archaeology and the search for the fossil records of the Galactic formation to tidal streams, dynamics, a validation of distances and extinction maps, and the characterisation of small scale extinction. This explains the renewed widespread interest in these stars within the astronomical community.

Previous *Gaia* data releases (Gaia Collaboration 2016, 2018) already showed the great potential of the mission in the field of stellar variability (Gaia Collaboration 2019) and for RR Lyrae stars and Cepheids in particular (Gaia Collaboration 2017; Clementini et al. 2016, hereafter Paper I; Clementini et al. 2019, hereafter Paper II). The potential is based on the multi-epoch nature and almost simultaneous acquisition of the

(spectro-)photometry, astrometry and spectroscopy data collected by *Gaia* throughout the celestial sphere.

The small sample of RR Lyrae stars and Cepheids in the Large Magellanic Cloud (LMC; about 3200 sources in total) published with *Gaia* Data Release 1 (DR1; Paper I) were only a tease of the samples and data products published for these pulsating stars in subsequent *Gaia* releases. Multi-band time-series photometry and pulsation characteristics were published in *Gaia* Data Release 2 (DR2; Gaia Collaboration 2018) for a catalogue of about 140 000 RR Lyrae stars and for about 10 000 Cepheids observed in the whole Galaxy (including 87 globular clusters and 14 MW companions) during the first 22 months of *Gaia* operation (Paper II). The number of RR Lyrae has now almost doubled, and that of Cepheids has increased by 50% compared to DR2 because of the larger amount of data and extended time baseline (34 months) spanned by *Gaia* Data Release 3 (DR3).

On 13 June 2022, *Gaia* DR3 (Gaia Collaboration 2023) multiband ($G$, $G_{BP}$, and $G_{RP}$) light curves were released for 270 905 RR Lyrae stars together with 15 006 Cepheids that were confirmed and fully characterised by the Specific Object Study pipeline for Cepheids and RR Lyrae (hereafter, SOS Cep&RRL; Papers I and II) developed within the *Gaia* Data Processing and Analysis Consortium (DPAC). Radial velocity (RV) time-series measurements obtained with the Radial Velocity Spectrometer (RVS; Cropper et al. 2018) on board *Gaia* for a sub-sample comprising 1096 RR Lyrae stars and 799 Cepheids (Ripepi et al. 2023) validated by the SOS Cep&RRL pipeline are also published with DR3. These numbers all refer to samples that were cleaned from contaminants and sources with an uncertain classification.

In this paper we present the changes that were implemented in the SOS Cep&RRL pipeline with respect to DR2. We describe in particular a new module that was activated to process the RVS time-series data and explain how the RR Lyrae and Cepheid variables with epoch RVs published in DR3 were selected. We then focus on the procedures and validations that led to the production of the final clean sample of confirmed RR Lyrae stars released in DR3. The processing and validation of the confirmed DR3 Cepheids are instead described in a companion paper (Ripepi et al. 2023).

The characteristic parameters derived by the SOS pipeline for the final sample of *Gaia* DR3 RR Lyrae stars that are published in the *vari_errlyrae* table include the pulsation period(s), peak-to-peak amplitudes of the *G*, $G_{BP}$, and $G_{RP}$ [Amp(*G*), Amp(*G*<sub>BP</sub>), Amp(*G*<sub>RP</sub>)] light curves, classification into type/pulsation mode (RRab, RRc, and RRd), and the mean magnitudes computed as an intensity average over the full pulsation cycle, along with the $\phi_{21}$, $\phi_{31}$, $R_{21}$, and $R_{31}$ parameters of the Fourier decomposition of the *G*-band light curves. Metallicities ([Fe/H]) computed from a relation that was found to exist with the pulsation period and the $\phi_{31}$ Fourier parameter of the RR Lyrae light curves (Jurcsik & Kovacs 1996; Nemec et al. 2013) and individual absorption values derived from the relation existing with the pulsation period, the colour and the amplitude of the light variation (Piersimoni et al. 2002) are also released for about a half of the whole SOS RR Lyrae sample. Amplitudes of the RV curves and mean RV values that were computed after modelling the RV curves are also provided in the DR3 *vari_errlyrae* and *vari-cepheid* tables for sub-samples of RR Lyrae stars and Cepheids.

The paper is organised as follows. In Sect. 2 we provide a brief overview of the SOS Cep&RRL pipeline and describe the changes and developments that were implemented
# 1. Introduction

RR Lyrae are low-mass (typical masses around 0.6–0.8 $M_\odot$), old (ages exceeding 9–10 billion years) stars whose surface expands and contracts regularly with periods shorter than one day. The pulsation gives rise to a variation in brightness that occurs in two main flavours. The light curves of c-type RR Lyrae (RRc) stars are almost sinusoidal. They repeat in time with periodicities of typically between about 0.2 and 0.42 day (d), and an amplitude in light variation of up to about half a magnitude in the visual band. RRc stars oscillate in the radial first-overtone pulsation mode. The ab-type RR Lyrae (RRab) stars have asymmetrical sawtooth light curves, periods of typically between about 0.42 and 1 d, and visual amplitudes in the *Gaia* *G* band from above 0.1 to more than one magnitude. They pulsate in the fundamental pulsation mode. In a small fraction of RR Lyrae stars, fundamental and first-overtone pulsation modes are excited at the same time, giving rise to the double-mode (d-type) RR Lyrae (RRd). The characteristic light variation makes RR Lyrae stars easily recognizable even in very crowded regions of the sky or in high-extinction conditions. Their pulsation characteristics (periods, amplitudes, mean magnitudes and colours, etc.) allow an estimate of their metal abundance and reddening, thus bringing invaluable added values (see e.g. Smith 1995; Catelan & Smith 2015, for comprehensive reviews of RR Lyrae stars).

RR Lyrae stars allow measuring the distance to the systems they live in because they follow luminosity–metallicity (LZ) relations in the visual bands (see e.g. Cacciari & Clementini 2003; Clementini et al. 2003; and references therein and e.g. Muraveva et al. 2018; Garofalo et al. 2022; for more recent LZ relations in the Johnson *V* and *Gaia* *G* bands, calibrated on *Gaia* parallaxes) and period–luminosity–(metallicity) (PLZ) relations in the infrared (see e.g. Muraveva et al. 2018; Bhardwaj et al. 2021, and references therein for PLZ relations in the $K_s$ and $W_1$ infrared bands). These variable stars are the only abundant stellar tracers with a small relative distance error (~5%), particularly at large distances. They therefore allow measuring the most accurate distances to old, distant stellar populations. Moreover, at 5–10 kpc from the Milky Way (MW) disc, they are also the stars with the most precise distances.

RR Lyrae stars are also excellent tracers of the oldest stars that witnessed the first epoch of galaxy formation. They can therefore provide indications about the building blocks that contributed to the build-up of galactic haloes (see e.g. Catelan & Smith 2015; Martínez-Vázquez et al. 2019, and references therein). All these properties make the RR Lyrae stars invaluable dynamical tracers of the Galaxy and a crucial tool for a plethora of applications, from Galactic archaeology and the search for the fossil records of the Galactic formation to tidal streams, dynamics, a validation of distances and extinction maps, and the characterization of small scale extinction. This explains the renewed widespread interest in these stars within the astronomical community.

Previous *Gaia* data releases (Gaia Collaboration 2016, 2018) already showed the great potential of the mission in the field of stellar variability (Gaia Collaboration 2019) and for RR Lyrae stars and Cepheids in particular (Gaia Collaboration 2017; Clementini et al. 2016, hereafter Paper I; Clementini et al. 2019, hereafter Paper II). The potential is based on the multi-epoch nature and almost simultaneous acquisition of the

(spectro-)photometry, astrometry and spectroscopy data collected by *Gaia* throughout the celestial sphere.

The small sample of RR Lyrae stars and Cepheids in the Large Magellanic Cloud (LMC; about 3200 sources in total) published with *Gaia* Data Release 1 (DR1; Paper I) were only a tease of the samples and data products published for these pulsating stars in subsequent *Gaia* releases. Multi-band time-series photometry and pulsation characteristics were published in *Gaia* Data Release 2 (DR2; Gaia Collaboration 2018) for a catalogue of about 140 000 RR Lyrae stars and for about 10 000 Cepheids observed in the whole Galaxy (including 87 globular clusters and 14 MW companions) during the first 22 months of *Gaia* operation (Paper II). The number of RR Lyrae has now almost doubled, and that of Cepheids has increased by 50% compared to DR2 because of the larger amount of data and extended time baseline (34 months) spanned by *Gaia* Data Release 3 (DR3).

On 13 June 2022, *Gaia* DR3 (Gaia Collaboration 2023) multiband ($G$, $G_{BP}$, and $G_{RP}$) light curves were released for 270 905 RR Lyrae stars together with 15 006 Cepheids that were confirmed and fully characterised by the Specific Object Study pipeline for Cepheids and RR Lyrae (hereafter, SOS Cep&RRL; Papers I and II) developed within the *Gaia* Data Processing and Analysis Consortium (DPAC). Radial velocity (RV) time-series measurements obtained with the Radial Velocity Spectrometer (RVS; Cropper et al. 2018) on board *Gaia* for a sub-sample comprising 1096 RR Lyrae stars and 799 Cepheids (Ripepi et al. 2023) validated by the SOS Cep&RRL pipeline are also published with DR3. These numbers all refer to samples that were cleaned from contaminants and sources with an uncertain classification.

In this paper we present the changes that were implemented in the SOS Cep&RRL pipeline with respect to DR2. We describe in particular a new module that was activated to process the RVS time-series data and explain how the RR Lyrae and Cepheid variables with epoch RVs published in DR3 were selected. We then focus on the procedures and validations that led to the production of the final clean sample of confirmed RR Lyrae stars released in DR3. The processing and validation of the confirmed DR3 Cepheids are instead described in a companion paper (Ripepi et al. 2023).

The characteristic parameters derived by the SOS pipeline for the final sample of *Gaia* DR3 RR Lyrae stars that are published in the *vari_errlyrae* table include the pulsation period(s), peak-to-peak amplitudes of the *G*, $G_{BP}$, and $G_{RP}$ [Amp(*G*), Amp(*G*<sub>BP</sub>), Amp(*G*<sub>RP</sub>)] light curves, classification into type/pulsation mode (RRab, RRc, and RRd), and the mean magnitudes computed as an intensity average over the full pulsation cycle, along with the $\phi_{21}$, $\phi_{31}$, $R_{21}$, and $R_{31}$ parameters of the Fourier decomposition of the *G*-band light curves. Metallicities ([Fe/H]) computed from a relation that was found to exist with the pulsation period and the $\phi_{31}$ Fourier parameter of the RR Lyrae light curves (Jurcsik & Kovacs 1996; Nemec et al. 2013) and individual absorption values derived from the relation existing with the pulsation period, the colour and the amplitude of the light variation (Piersimoni et al. 2002) are also released for about a half of the whole SOS RR Lyrae sample. Amplitudes of the RV curves and mean RV values that were computed after modelling the RV curves are also provided in the DR3 *vari_errlyrae* and *vari-cepheid* tables for sub-samples of RR Lyrae stars and Cepheids.

The paper is organised as follows. In Sect. 2 we provide a brief overview of the SOS Cep&RRL pipeline and describe the changes and developments that were implemented
<figure><img src="image_1.png" /><figcaption>**Fig. 1.** Schematic view of modules (rectangles) and outputs (parallelograms) of the SOS Cep&RRL pipeline main trunk. The figure is an updated version of Fig. 1 in Paper II. Changes and additions to the pipeline version used in DR2 are highlighted in boldface (see text for details).</figcaption></figure>

to process the Gaia DR3 photometry and RV time-series data. Section 3 presents the DR3 input data, the selections that were applied to run the pipeline on the RR Lyrae candidates, and results from the processing. Section 4 focuses on the analysis of the RVS RV time-series data for sub-samples of RR Lyrae stars and Cepheids for which RVS RV curves are published in DR3. Section 5 specifically discusses the astrophysical parameters (metallicity and G-band absorption values) we derived from the pulsation characteristics of RR Lyrae stars. The cleaning from contaminants, reclassifications, and a final validation of the RR Lyrae catalogue are described in Sect. 6. In Sect. 7 we discuss the completeness and purity of the clean catalogue of RR Lyrae stars published in DR3 and present colour-magnitude diagrams and sky maps defined by these RR Lyrae stars. Finally, conclusions and further developments of the SOS Cep&RRL pipeline in preparation for future Gaia data releases (DR4 and 5) are briefly discussed in Sect. 8.

## 2. SOS Cep&RRL pipeline: General overview and changes for DR3

The variability processing (see Gaia DR3 Documentation, Rimoldini et al. 2022)<fnref n="1" /> is based on the analysis of Gaia DR3 calibrated G and integrated $G_{BP}$ and $G_{RP}$ time-series photometry (Riello et al. 2021), and for RR Lyrae stars and Cepheids also on the RVS RV time-series (Sartoretti et al. 2022), through the various steps (modules) of the general variability analysis approach described in Eyer et al. (2017) and in Eyer et al. (2023) specifically for DR3. This includes identification and classification into different types of the variable candidates, which are then fed to the SOS pipelines, each of which is specifically tailored to validate and characterise a certain type of variability. Figure 10.1

in the Gaia DR3 Documentation (Rimoldini et al. 2022) shows a schematic view of the general variability processing before the data enter the SOS pipelines.

The SOS Cep&RRL pipeline is designed to validate and characterise all-sky candidate RR Lyrae stars and Cepheids identified in the Gaia G, $G_{BP}$, and $G_{RP}$ time-series photometry by the General Supervised Classification module (Rimoldini et al. 2023) in the variability analysis pipeline. This module uses machine-learning methods and multi-class supervised classifiers to classify Gaia time series of candidate variable objects into categories. A full description of the SOS Cep&RRL pipeline can be found in Papers I and II, to which we refer for details. In the following, we summarise steps of the pipeline that are the same for RR Lyrae stars and Cepheids (pipeline main trunk, Fig. 1) and the processing that takes place in the RR Lyrae branch (Fig. 2). The Cepheid branch is discussed in a companion paper (Ripepi et al. 2023).

The steps of the SOS Cep&RRL pipeline main trunk include

- a derivation of the source periodicity (P) with the Lomb-Scargle algorithm (Lomb 1976; Scargle 1982; see Sect. 2.1 in Paper I);

- modelling of the time-series data, folded according to the derived P, using the Levenberg-Marquardt (Levenberg 1944; Marquardt 1963) non-linear fitting algorithm (NonLinear-FourierAnalysis module in Fig. 1), which refines the period and model of the light curves;

- a derivation of the main parameters of the variable stars (intensity-averaged mean magnitudes; peak-to-peak amplitudes: Amp(G), Amp($G_{BP}$), and Amp($G_{RP}$); epoch of maximum light; etc.) from the light curves modelled with the non-linear fitting algorithm;

- Fourier decomposition of the G-band light curve and derivation of the Fourier parameters $\phi_{21}$, $\phi_{31}$, $R_{21}$, and $R_{31}$ using a Fourier expansion in cosine functions;

- a search for secondary periodicities.

<footnote n="1">¹ https://gea.esac.esa.int/archive/documentation/GDR3/</footnote>
<figure><img src="image_2.png" /><figcaption>**Fig. 1.** Schematic view of modules (rectangles) and outputs (parallelograms) of the SOS Cep&RRL pipeline main trunk. The figure is an updated version of Fig. 1 in Paper II. Changes and additions to the pipeline version used in DR2 are highlighted in boldface (see text for details).</figcaption></figure>

to process the Gaia DR3 photometry and RV time-series data. Section 3 presents the DR3 input data, the selections that were applied to run the pipeline on the RR Lyrae candidates, and results from the processing. Section 4 focuses on the analysis of the RVS RV time-series data for sub-samples of RR Lyrae stars and Cepheids for which RVS RV curves are published in DR3. Section 5 specifically discusses the astrophysical parameters (metallicity and G-band absorption values) we derived from the pulsation characteristics of RR Lyrae stars. The cleaning from contaminants, reclassifications, and a final validation of the RR Lyrae catalogue are described in Sect. 6. In Sect. 7 we discuss the completeness and purity of the clean catalogue of RR Lyrae stars published in DR3 and present colour-magnitude diagrams and sky maps defined by these RR Lyrae stars. Finally, conclusions and further developments of the SOS Cep&RRL pipeline in preparation for future Gaia data releases (DR4 and 5) are briefly discussed in Sect. 8.

## 2. SOS Cep&RRL pipeline: General overview and changes for DR3

The variability processing (see Gaia DR3 Documentation, Rimoldini et al. 2022)<fnref n="1" /> is based on the analysis of Gaia DR3 calibrated G and integrated $G_{BP}$ and $G_{RP}$ time-series photometry (Riello et al. 2021), and for RR Lyrae stars and Cepheids also on the RVS RV time-series (Sartoretti et al. 2022), through the various steps (modules) of the general variability analysis approach described in Eyer et al. (2017) and in Eyer et al. (2023) specifically for DR3. This includes identification and classification into different types of the variable candidates, which are then fed to the SOS pipelines, each of which is specifically tailored to validate and characterise a certain type of variability. Figure 10.1

in the Gaia DR3 Documentation (Rimoldini et al. 2022) shows a schematic view of the general variability processing before the data enter the SOS pipelines.

The SOS Cep&RRL pipeline is designed to validate and characterise all-sky candidate RR Lyrae stars and Cepheids identified in the Gaia G, $G_{BP}$, and $G_{RP}$ time-series photometry by the General Supervised Classification module (Rimoldini et al. 2023) in the variability analysis pipeline. This module uses machine-learning methods and multi-class supervised classifiers to classify Gaia time series of candidate variable objects into categories. A full description of the SOS Cep&RRL pipeline can be found in Papers I and II, to which we refer for details. In the following, we summarise steps of the pipeline that are the same for RR Lyrae stars and Cepheids (pipeline main trunk, Fig. 1) and the processing that takes place in the RR Lyrae branch (Fig. 2). The Cepheid branch is discussed in a companion paper (Ripepi et al. 2023).

The steps of the SOS Cep&RRL pipeline main trunk include

- a derivation of the source periodicity (P) with the Lomb-Scargle algorithm (Lomb 1976; Scargle 1982; see Sect. 2.1 in Paper I);

- modelling of the time-series data, folded according to the derived P, using the Levenberg-Marquardt (Levenberg 1944; Marquardt 1963) non-linear fitting algorithm (NonLinear-FourierAnalysis module in Fig. 1), which refines the period and model of the light curves;

- a derivation of the main parameters of the variable stars (intensity-averaged mean magnitudes; peak-to-peak amplitudes: Amp(G), Amp($G_{BP}$), and Amp($G_{RP}$); epoch of maximum light; etc.) from the light curves modelled with the non-linear fitting algorithm;

- Fourier decomposition of the G-band light curve and derivation of the Fourier parameters $\phi_{21}$, $\phi_{31}$, $R_{21}$, and $R_{31}$ using a Fourier expansion in cosine functions;

- a search for secondary periodicities.

<footnote n="1">¹ https://gea.esac.esa.int/archive/documentation/GDR3/</footnote>
<figure><img src="image_2.png" /><figcaption>**Fig. 2.** Modules and outputs of the RR Lyrae branch of the SOS Cep&RRL pipeline. As in Fig. 1, changes with respect to DR2 are highlighted in boldface. Three modules that were not activated for DR3 are shown in grey (see text for details).</figcaption></figure>

The following diagnostic tools and combination of parameters are used in the RR Lyrae branch to extract bona fide RR Lyrae stars from the candidates, classify them into types (RRc, RRab, RRd) and pulsation mode (first overtone, fundamental mode, and double mode), and derive their astrophysical parameters [metallicity – [Fe/H], and absorption in the *G*-band – *A*(*G*)],

- pulsation period (P) versus Amp(*G*) diagram (*PA*);

- $\phi_{21}$ versus *P* diagram;

- $R_{21}$ versus *P* diagram;

- $\phi_{31}$ versus *P* diagram;

- $R_{31}$ versus *P* diagram;

- [Fe/H] versus *P*, $\phi_{31}$ relation;

- $A(*G*)$ versus Amp(*G*), *P*, (*G* − $G_{RP}$) relation.

A number of changes were implemented and new parts of the pipeline were activated to process the DR3 RR Lyrae and Cepheid candidates. We have highlighted them in boldface in Figs. 1 and 2 and describe below those that occur in (and before) the pipeline main trunk and the RR Lyrae branch. A detailed description of the changes implemented in the Cepheid branch (improved detection of multimode Cepheids, adoption of new period-luminosity and period-Wesenheit relations directly computed in the *Gaia* passbands for the different types of Cepheids, etc.) is presented in Ripepi et al. (2023).

- Optimisation of outlier-removal operators

Outliers and measurements of poor quality in the *Gaia* photometry and RV time-series data are filtered out by operators of the general variability pipeline, whose configuration parameters can be adapted to the specific type of variable sources under investigation. In the main chain of operators that are applied sequentially to transform and filter the input photometric time series, the *RemoveOutliersFaintAndBrightOperator* (ROFABO) that was adopted for DR2, was replaced by the *MultibandOutlierRemovalOperator* (MORO) (see Sect. 10.2.3.2 in *Gaia* DR3 Documentation, Rimoldini et al. 2022; Eyer et al. 2023).

MORO identifies outliers from comparing the measurements in the three *Gaia* photometric bands. However, a ROFABO step, with configuration parameters we specifically tailored to RR Lyrae and Cepheid variables, was also added to the operators chain to improve the rejection of poor measurements in the time-series photometry of sources processed through the SOS Cep&RRL pipeline.

An *RvsOutlierRemovalOperator* that applies a similar approach as the ROFABO was also applied to clean the RVS time-series data (see Rimoldini et al. 2022, for details).

- Processing of RVS radial velocity time series.

A specific routine was activated that processes the RVS time-series RV measurements. The routine constructs the Fourier model of the RV curve obtained by folding the data according to the period inferred from the *G*-band time-series photometry and returns the Fourier amplitudes and phases, the peak-to-peak amplitude of the RV curve [Amp(RV)], the mean RV, and the epoch of minimum RV value.

- Error estimate via the bootstrap technique.

Errors for all the parameters of the RR Lyrae stars and Cepheids that were processed and confirmed by the SOS pipeline for DR3 were estimated via a bootstrap technique that replaced the Monte Carlo simulations (consisting of randomly varying the data within their errors) adopted for DR1 and DR2 (Papers I and II). Specifically, errors on the Fourier fit parameters (period, amplitudes, and phases) and the quantities characterising the light and RV curves (mean magnitudes, mean velocity, peak-to-peak amplitudes, etc.) were estimated by randomly resampling the input data (allowing data point repetitions), and the parameters were recalculated from the resulting simulated sample. The procedure was repeated 100 times, and for each parameter, the error was estimated from the robust standard deviation (1.486 × MAD, where MAD is the median absolute deviation) of the resulting bootstrap distributions. A similar procedure was
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** Modules and outputs of the RR Lyrae branch of the SOS Cep&RRL pipeline. As in Fig. 1, changes with respect to DR2 are highlighted in boldface. Three modules that were not activated for DR3 are shown in grey (see text for details).</figcaption></figure>

The following diagnostic tools and combination of parameters are used in the RR Lyrae branch to extract bona fide RR Lyrae stars from the candidates, classify them into types (RRc, RRab, RRd) and pulsation mode (first overtone, fundamental mode, and double mode), and derive their astrophysical parameters [metallicity – [Fe/H], and absorption in the *G*-band – *A*(*G*)],

- pulsation period (P) versus Amp(*G*) diagram (PA);

- $\phi_{21}$ versus *P* diagram;

- $R_{21}$ versus *P* diagram;

- $\phi_{31}$ versus *P* diagram;

- $R_{31}$ versus *P* diagram;

- [Fe/H] versus *P*, $\phi_{31}$ relation;

- $A(*G*)$ versus Amp(*G*), *P*, (*G* − $G_{RP}$) relation.

A number of changes were implemented and new parts of the pipeline were activated to process the DR3 RR Lyrae and Cepheid candidates. We have highlighted them in boldface in Figs. 1 and 2 and describe below those that occur in (and before) the pipeline main trunk and the RR Lyrae branch. A detailed description of the changes implemented in the Cepheid branch (improved detection of multimode Cepheids, adoption of new period-luminosity and period-Wesenheit relations directly computed in the *Gaia* passbands for the different types of Cepheids, etc.) is presented in Ripepi et al. (2023).

- Optimisation of outlier-removal operators

Outliers and measurements of poor quality in the *Gaia* photometry and RV time-series data are filtered out by operators of the general variability pipeline, whose configuration parameters can be adapted to the specific type of variable sources under investigation. In the main chain of operators that are applied sequentially to transform and filter the input photometric time series, the *RemoveOutliersFaintAndBrightOperator* (ROFABO) that was adopted for DR2, was replaced by the *MultibandOutlierRemovalOperator* (MORO) (see Sect. 10.2.3.2 in *Gaia* DR3 Documentation, Rimoldini et al. 2022; Eyer et al. 2023).

MORO identifies outliers from comparing the measurements in the three *Gaia* photometric bands. However, a ROFABO step, with configuration parameters we specifically tailored to RR Lyrae and Cepheid variables, was also added to the operators chain to improve the rejection of poor measurements in the time-series photometry of sources processed through the SOS Cep&RRL pipeline.

An *RvsOutlierRemovalOperator* that applies a similar approach as the ROFABO was also applied to clean the RVS time-series data (see Rimoldini et al. 2022, for details).

- Processing of RVS radial velocity time series.

A specific routine was activated that processes the RVS time-series RV measurements. The routine constructs the Fourier model of the RV curve obtained by folding the data according to the period inferred from the *G*-band time-series photometry and returns the Fourier amplitudes and phases, the peak-to-peak amplitude of the RV curve [Amp(RV)], the mean RV, and the epoch of minimum RV value.

- Error estimate via the bootstrap technique.

Errors for all the parameters of the RR Lyrae stars and Cepheids that were processed and confirmed by the SOS pipeline for DR3 were estimated via a bootstrap technique that replaced the Monte Carlo simulations (consisting of randomly varying the data within their errors) adopted for DR1 and DR2 (Papers I and II). Specifically, errors on the Fourier fit parameters (period, amplitudes, and phases) and the quantities characterising the light and RV curves (mean magnitudes, mean velocity, peak-to-peak amplitudes, etc.) were estimated by randomly resampling the input data (allowing data point repetitions), and the parameters were recalculated from the resulting simulated sample. The procedure was repeated 100 times, and for each parameter, the error was estimated from the robust standard deviation (1.486 × MAD, where MAD is the median absolute deviation) of the resulting bootstrap distributions. A similar procedure was
also applied to estimate random errors of other attributes released for RR Lyrae stars, such as metal abundances and absorption values.

- New and revised sky sub-regions.

The last module of the main trunk of the pipeline subdi-vides the sources according to different regions on the sky before sending them to the RR Lyrae and Cepheid branches. This is because different relations are needed to classify the sources depending on their position on the sky (see Paper II). For DR2, we divided the sky into three separate regions: the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), and all-sky, comprising the remaining part of the sky. The LMC and SMC regions were expanded for DR3. The new region for the LMC is a box centred on the galaxy at $RA_{LMC} (J2000) = 82.5°$, $Dec_{LMC} (J2000) = -68.25°$ and extending from 67.50° to 97.50° in RA and from -75.00° to -62.00° in Dec. Similarly, the new region for the SMC is a box centred at $RA_{SMC} (J2000) = 16°$, $Dec_{SMC} (J2000) = -73°$ and extending from 0.00° to 30.00° in RA and from -76.00° to -70.00° in Dec. Two further regions were also defined, one centred on the Andromeda galaxy (M31) and one around the Triangulum galaxy (M33), to allow the processing of bright Cepheids within the reach of Gaia in these galaxies. The details of these two additional regions are provided in Ripepi et al. (2023).

In DR2, a number of Cepheids with a G-band amplitude smaller than 0.5 mag and periods shorter than 1 d were missed or misclassified as RR Lyrae stars. A change was implemented in the SOS pipeline for DR3 by which sources classified as RR Lyrae stars at the end of the common trunk in Fig. 1 were sent to both the RR Lyrae and the Cepheid branches if they belonged to the region of the sky and satisfied the conditions described below.

- All-Sky sources with an available parallax were always sent to both branches;

- Sources in the LMC and in the SMC sub-regions (as defined above) with an amplitude smaller than 0.5 mag, periods shorter than 1 d, and a mean G magnitude brighther than 18.5 and 19 mag in the LMC and SMC, respectively;

- All sources with $P \le 1$ d in the M31 and M33 sub-regions.

This procedure caused a number of sources to have a double classification. They were checked and finally classified into just one class (RR Lyrae star or Cepheid; see Sects. 3.2 and 3.3).

Two main changes were implemented in the RR Lyrae branch (Fig. 2) of the SOS pipeline. They are briefly described below.

- Improvement of double-mode RR Lyrae detection

The module to search for a secondary periodicity in the time-series photometry of RR Lyrae stars was activated only for sources with more than 40 measurements (FoV transits) in the G-band time-series data and when residuals from the Fourier model that best fits the G-band light curve folded with the primary period were higher than 0.05 mag. This allowed us to reduce the number of spurious double-mode RR Lyrae detections significantly.

- Implementation of new thresholds in the PA diagnostic

The PA diagram is used by the SOS pipeline to separate fundamental-mode and first-overtone RR Lyrae stars (see Fig. 4 in Paper II). For DR1 and DR2, we applied a straight line to separate the RRab and RRc regions. For DR3, we have defined new boundaries of the two regions in order to properly distinguish high-amplitude short-period RRab from RRc stars. The new boundaries are shown as red seg-ments (described by the condition $Amp(G) \le 0.64$ mag for $P \le 0.34$ d) that replaced the dotted portion of the straight

<figure><img src="image_3.png" /><figcaption>**Fig. 3.** New boundaries of the RRab and RRc regions in the PA dia-gram defined by a sample of about 15 000 RR Lyrae stars that was randomly selected from the final RR Lyrae catalogue published in the dr3_variDOCUMENTARY table of Gaia DR3. The dotted portion of the black line separating RRab from RRc stars was replaced by the broken red line in order to properly classify high-amplitude RRab stars with pulsation periods in the same domain as RRc stars (see text for details).</figcaption></figure>

black line in Fig. 3. All sources below the red segments and the solid black line are classified as RRc stars, and sources above these lines are RRab stars. However, the new thresh-olds were not able to capture all such short-period RRab stars (see Sect. 6.1). A more efficient procedure will be imple-mented for Gaia DR4 that specifically takes into account the much steeper rise to maximum light of RRab compared to RRc stars. This will help to better distinguish the two types.

Finally, we show in grey in Fig. 2 three modules that were not activated for DR3. The amplitude ratio routine, although not operational during the SOS processing, was used during validation to compute $AmpG/AmpG_{BP}$, $AmpG/AmpG_{RP}$, and $AmpG_{BP}/AmpG_{RP}$ ratios and to identify eclipsing binaries that contaminate the RR Lyrae sample (see Sect. 6).

## 3. Application of the SOS Cep&RRL pipeline to the DR3 dataset: Input data and source selections

Input data fed into the SOS Cep&RRL pipeline in DR3 con-sisted of FoV G and integrated $G_{BP}$ and $G_{RP}$ (when available) time-series photometry of all-sky variable sources classified as RR Lyrae (and Cepheids; see Ripepi et al. 2023) candidates with various probability values by the General Supervised Classifica-tion module (Rimoldini et al. 2023; see Fig. 1) of the variability pipeline, as well as RV time-series data from the RVS for small subsamples of these sources with a mean magnitude brighter than $G_{RVS} \sim 14$ mag<fnref n="2" />. The photometry and RV datasets com-prise observations collected by Gaia over 34 months, from 25 July 2014 to 28 May 2017. For the confirmed RR Lyrae stars discussed in this paper, Gaia obtained about 38–39 useful pho-tometric measurements in the G band on average in this time frame (with minimum and maximum values between 12 and 257 measures, depending on the source position on sky; Fig. 4, cen-tre panel), which is to be compared with $\sim 30$ G measures in DR2 and about 30 measurements in $G_{BP}$ (with minimum and maximum values between 0 and 258; Fig. 4, left panel) and $G_{RP}$

<footnote n="2">² $G_{RVS}$ is the Gaia magnitude of the flux collected in the RVS pass-band: 845–872 nm. For the transformation from $G_{RVS}$ to G magnitude, see Eq. (2) in Gaia Collaboration (2018). In practice, $G - G_{RVS} \sim 0.48$ and 0.45 mag for RRc and RRab stars, respectively.</footnote>
also applied to estimate random errors of other attributes released for RR Lyrae stars, such as metal abundances and absorption values.

- New and revised sky sub-regions.

The last module of the main trunk of the pipeline subdi-vides the sources according to different regions on the sky before sending them to the RR Lyrae and Cepheid branches. This is because different relations are needed to classify the sources depending on their position on the sky (see Paper II). For DR2, we divided the sky into three separate regions: the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), and all-sky, comprising the remaining part of the sky. The LMC and SMC regions were expanded for DR3. The new region for the LMC is a box centred on the galaxy at $RA_{LMC}(J2000) = 82.5°$, $Dec_{LMC}(J2000) = -68.25°$ and extending from 67.50° to 97.50° in RA and from -75.00° to -62.00° in Dec. Similarly, the new region for the SMC is a box centred at $RA_{SMC}(J2000) = 16°$, $Dec_{SMC}(J2000) = -73°$ and extending from 0.00° to 30.00° in RA and from -76.00° to -70.00° in Dec. Two further regions were also defined, one centred on the Andromeda galaxy (M31) and one around the Triangulum galaxy (M33), to allow the processing of bright Cepheids within the reach of Gaia in these galaxies. The details of these two additional regions are provided in Ripepi et al. (2023).

In DR2, a number of Cepheids with a G-band amplitude smaller than 0.5 mag and periods shorter than 1 d were missed or misclassified as RR Lyrae stars. A change was implemented in the SOS pipeline for DR3 by which sources classified as RR Lyrae stars at the end of the common trunk in Fig. 1 were sent to both the RR Lyrae and the Cepheid branches if they belonged to the region of the sky and satisfied the conditions described below.

- All-Sky sources with an available parallax were always sent to both branches;

- Sources in the LMC and in the SMC sub-regions (as defined above) with an amplitude smaller than 0.5 mag, periods shorter than 1 d, and a mean G magnitude brighter than 18.5 and 19 mag in the LMC and SMC, respectively;

- All sources with $P \le 1$ d in the M31 and M33 sub-regions.

This procedure caused a number of sources to have a double classification. They were checked and finally classified into just one class (RR Lyrae star or Cepheid; see Sects. 3.2 and 3.3).

Two main changes were implemented in the RR Lyrae branch (Fig. 2) of the SOS pipeline. They are briefly described below.

- Improvement of double-mode RR Lyrae detection

The module to search for a secondary periodicity in the time-series photometry of RR Lyrae stars was activated only for sources with more than 40 measurements (FoV transits) in the G-band time-series data and when residuals from the Fourier model that best fits the G-band light curve folded with the primary period were higher than 0.05 mag. This allowed us to reduce the number of spurious double-mode RR Lyrae detections significantly.

- Implementation of new thresholds in the PA diagnostic

The PA diagram is used by the SOS pipeline to separate fundamental-mode and first-overtone RR Lyrae stars (see Fig. 4 in Paper II). For DR1 and DR2, we applied a straight line to separate the RRab and RRc regions. For DR3, we have defined new boundaries of the two regions in order to properly distinguish high-amplitude short-period RRab from RRc stars. The new boundaries are shown as red seg-ments (described by the condition $Amp(G) \le 0.64$ mag for $P \le 0.34$ d) that replaced the dotted portion of the straight

<figure><img src="image_4.png" /><figcaption>Fig. 3. New boundaries of the RRab and RRc regions in the PA dia-gram defined by a sample of about 15 000 RR Lyrae stars that was randomly selected from the final RR Lyrae catalogue published in the dr3_variDOCUMENTARY table of Gaia DR3. The dotted portion of the black line separating RRab from RRc stars was replaced by the broken red line in order to properly classify high-amplitude RRab stars with pulsation periods in the same domain as RRc stars (see text for details).</figcaption></figure>

black line in Fig. 3. All sources below the red segments and the solid black line are classified as RRc stars, and sources above these lines are RRab stars. However, the new thresh-olds were not able to capture all such short-period RRab stars (see Sect. 6.1). A more efficient procedure will be imple-mented for Gaia DR4 that specifically takes into account the much steeper rise to maximum light of RRab compared to RRc stars. This will help to better distinguish the two types.

Finally, we show in grey in Fig. 2 three modules that were not activated for DR3. The amplitude ratio routine, although not operational during the SOS processing, was used during validation to compute $AmpG/AmpG_{BP}$, $AmpG/AmpG_{RP}$, and $AmpG_{BP}/AmpG_{RP}$ ratios and to identify eclipsing binaries that contaminate the RR Lyrae sample (see Sect. 6).

## 3. Application of the SOS Cep&RRL pipeline to the DR3 dataset: Input data and source selections

Input data fed into the SOS Cep&RRL pipeline in DR3 con-sisted of FoV G and integrated $G_{BP}$ and $G_{RP}$ (when available) time-series photometry of all-sky variable sources classified as RR Lyrae (and Cepheids; see Ripepi et al. 2023) candidates with various probability values by the General Supervised Classifica-tion module (Rimoldini et al. 2023; see Fig. 1) of the variability pipeline, as well as RV time-series data from the RVS for small subsamples of these sources with a mean magnitude brighter than $G_{RVS} \sim 14$ mag<fnref n="2" />. The photometry and RV datasets com-prise observations collected by Gaia over 34 months, from 25 July 2014 to 28 May 2017. For the confirmed RR Lyrae stars discussed in this paper, Gaia obtained about 38–39 useful pho-tometric measurements in the G band on average in this time frame (with minimum and maximum values between 12 and 257 measures, depending on the source position on sky; Fig. 4, cen-tre panel), which is to be compared with $\sim 30$ G measures in DR2 and about 30 measurements in $G_{BP}$ (with minimum and maximum values between 0 and 258; Fig. 4, left panel) and $G_{RP}$

<footnote n="2">² $G_{RVS}$ is the Gaia magnitude of the flux collected in the RVS pass-band: 845–872 nm. For the transformation from $G_{RVS}$ to G magnitude, see Eq. (2) in Gaia Collaboration (2018). In practice, $G - G_{RVS} \sim 0.48$ and 0.45 mag for RRc and RRab stars, respectively.</footnote>
<figure><img src="image_4.png" /><figcaption>**Fig. 4.** Distribution in number of epochs in the *Gaia* $G_{BP}$ (left), *G* (centre), and $G_{RP}$ (right) passbands of the 271 779 RR Lyrae stars confirmed by the SOS Cep&RRL pipeline.</figcaption></figure>

(with minimum and maximum values between 0 and 254; Fig. 4, right panel). Similarly, the *Gaia* RVS time-series data for the sub-samples of RR Lyrae and Cepheids presented in Sect. 4 comprise an average of about 23 RV measurements (minimum and maximum values between 5 and 77). The following criteria were applied to select RR Lyrae candidates to process with the SOS Cep&RRL pipeline:

- sources classified as RR Lyrae candidates by the classifiers of the General Supervised Classification module, with minimum probability thresholds chosen to maximise the recovery of RR Lyrae stars known from different surveys in the literature (see Sect. 3.1);

- sources with at least 12 *G* FoV transits after the MORO and ROFABO outlier removal operators were applied (see Fig. 4);

- at least five measurements for the publication of the RV time series and at least seven transits for the modelling of the folded RV curve;

- a peak-to-peak amplitude >0.1 mag in the *G* band;

- periods in the range of $0.2 \le P < 1.0$ d.

### 3.1. Training sets and literature reference catalogues

Candidate RR Lyrae stars to be processed through the SOS Cep&RRL pipeline were selected on the basis of their probability score to maximise the recovery of RR Lyrae stars that are already known in the literature. A preliminary step was the creation of a reference database of known RR Lyrae stars by collecting catalogues of these variables from major surveys in the literature, including those in 152 different stellar systems: the Magellanic Clouds, 107 globular clusters, nine dwarf spheroidal galaxies (dSphs; Carina, Draco, Fornax, Leo I, Leo II, Sagittarius, Sculptor, Sextans, and Ursa Minor) and 34 ultra-faint dwarfs (UFDs). This large catalogue, homogenised by eliminating duplicates, contains more than 425 000 unique all-sky RR Lyrae entries and spans a range of about 16 mag from RR Lyr itself ($\langle V \rangle = 7.76$ mag; Fernley et al. 1998) to V6, the lone RR Lyrae star identified in Leo T (Clementini et al. 2012), an ultra-faint dwarf galaxy located at about 400 kpc in distance from the MW. The mean magnitude of V6, $\langle V \rangle = 23.59$ mag, is lower than the *Gaia* faint limit by about 3 mag. However, we note that 97% of the sources in our custom RR Lyrae catalogue are within the limiting magnitude of *Gaia* and have a counterpart in the EDR3 *source_table* (see below). To build our custom catalogue, we primarily used the OGLE catalogues for RR Lyrae stars as reference (version IV of the survey; Soszyński et al. 2014, 2019), which have a high completeness and purity for the LMC, SMC, and the MW bulge and disc, along with the *Gaia* DR2 RR Lyrae catalogue in the *gaiadr2.vari_rrlyrae* table (Paper II), CATALINA (Drake et al. 2013, 2014, 2017; Torrealba et al. 2015), KEPLER (Molnár et al. 2018), the *Zwicky Transient Facility* (ZTF; Chen et al. 2020), the All-Sky Automated Survey (ASAS;

Pojmanski 2000, 2002; Pigulski et al. 2009), the All-Sky Automated Survey for Supernovae (ASAS-SN; Jayasinghe et al. 2019), LINEAR (Palaversa et al. 2013; Sesar et al. 2013), the Palomar Transient Factory (PTF; Sesar et al. 2014), the VISTA Variables in the Via Lactea survey (VVV; Contreras Ramos et al. 2018; Dékány et al. 2018), the fifth edition of the General Catalogue of Variable Stars (GCVS; Samus' et al. 2017), and the PanSTARRS1 $3\pi$ survey (PS1; Sesar et al. 2017). To integrate our compilation with known RR Lyrae stars in Galactic globular clusters (GCs), we used an updated version of the Variable Stars in Galactic Globular Clusters catalogue (Clement et al. 2001) as main reference, and for RR Lyrae stars in the MW UFDs, we used the compilation in Vivas et al. (2020). For the MW dSphs, we used the RR Lyrae collections by Muraveva et al. (2020) for Draco, Martínez-Vázquez et al. (2016) for Sculptor, Bersier & Wood (2002) for Fornax, Coppola et al. (2015) for Carina, Siegel & Majewski (2000) for Leo II, Stetson et al. (2014) for Leo I, Vivas et al. (2019) for Sextans, Kunder et al. (2008) for Sagittarius, and the collections by Nemec et al. (1988) and Bellazzini et al. (2002) for Ursa Minor.

We specifically note that in building our custom RR Lyrae catalogue, we gave preference to inclusiveness. We therefore did not make any cut for purity. For the selection procedures described in the following sections, we used a version frozen at December 2020 of our custom RR Lyrae catalogue. However, the catalogue is being regularly updated as soon as new RR Lyrae compilations appear in the literature, and we plan to make a most recently updated version available online after *Gaia* DR3 (Garofalo et al., in prep.).

We performed a spatial cross-match within a $2.5''$ paring radius of our custom RR Lyrae catalogue and sources in the *gaia_source* table of the *Gaia* EDR3 archive (*gaiaedr3.gaiasource*) and found a counterpart in the EDR3 main catalogue for 414 082 (97%) of the RR Lyrae stars in our collection<fnref n="3" />. The classifiers of the General Supervised Classification module in the variability analysis pipeline returned these 414 082 sources as RR Lyrae candidates with probabilities starting from very low values. More than 75% (311 798) were classified as RR Lyrae by the SOS Cep&RRL pipeline. Characteristic parameters (*P*, pulsation mode, etc.) consistent with the literature were recovered for about 65% of them.

### 3.2. Gold Sample and validation criteria

In order to validate the unexpectedly large number of candidate RR Lyrae produced by the classifiers and confirmed by the SOS Cep&RRL pipeline and to extract a bona fide sample to release in DR3, we adopted a strategy based on our custom

<footnote n="3">³ We refer to Gavras et al. (2023) for a comprehensive catalogue of known variable sources cross-matched with *Gaia* DR3. This also extends our catalogue to other types of variability.</footnote>
<figure><img src="image_5.png" /><figcaption>**Fig. 4.** Distribution in number of epochs in the *Gaia* $G_{BP}$ (left), *G* (centre), and $G_{RP}$ (right) passbands of the 271 779 RR Lyrae stars confirmed by the SOS Cep&RRL pipeline.</figcaption></figure>

(with minimum and maximum values between 0 and 254; Fig. 4, right panel). Similarly, the *Gaia* RVS time-series data for the sub-samples of RR Lyrae and Cepheids presented in Sect. 4 comprise an average of about 23 RV measurements (minimum and maximum values between 5 and 77). The following criteria were applied to select RR Lyrae candidates to process with the SOS Cep&RRL pipeline:

- sources classified as RR Lyrae candidates by the classifiers of the General Supervised Classification module, with minimum probability thresholds chosen to maximise the recovery of RR Lyrae stars known from different surveys in the literature (see Sect. 3.1);

- sources with at least 12 G FoV transits after the MORO and ROFABO outlier removal operators were applied (see Fig. 4);

- at least five measurements for the publication of the RV time series and at least seven transits for the modelling of the folded RV curve;

- a peak-to-peak amplitude >0.1 mag in the *G* band;

- periods in the range of $0.2 \le P < 1.0$ d.

### 3.1. Training sets and literature reference catalogues

Candidate RR Lyrae stars to be processed through the SOS Cep&RRL pipeline were selected on the basis of their probability score to maximise the recovery of RR Lyrae stars that are already known in the literature. A preliminary step was the creation of a reference database of known RR Lyrae stars by collecting catalogues of these variables from major surveys in the literature, including those in 152 different stellar systems: the Magellanic Clouds, 107 globular clusters, nine dwarf spheroidal galaxies (dSphs; Carina, Draco, Fornax, Leo I, Leo II, Sagittarius, Sculptor, Sextans, and Ursa Minor) and 34 ultra-faint dwarfs (UFDs). This large catalogue, homogenised by eliminating duplicates, contains more than 425 000 unique all-sky RR Lyrae entries and spans a range of about 16 mag from RR Lyr itself ($\langle V \rangle = 7.76$ mag; Fernley et al. 1998) to V6, the lone RR Lyrae star identified in Leo T (Clementini et al. 2012), an ultra-faint dwarf galaxy located at about 400 kpc in distance from the MW. The mean magnitude of V6, $\langle V \rangle = 23.59$ mag, is lower than the *Gaia* faint limit by about 3 mag. However, we note that 97% of the sources in our custom RR Lyrae catalogue are within the limiting magnitude of *Gaia* and have a counterpart in the EDR3 *source_table* (see below). To build our custom catalogue, we primarily used the OGLE catalogues for RR Lyrae stars as reference (version IV of the survey; Soszyński et al. 2014, 2019), which have a high completeness and purity for the LMC, SMC, and the MW bulge and disc, along with the *Gaia* DR2 RR Lyrae catalogue in the *gaiadr2.vari_rrlyrae* table (Paper II), CATALINA (Drake et al. 2013, 2014, 2017; Torrealba et al. 2015), KEPLER (Molnár et al. 2018), the *Zwicky Transient Facility* (ZTF; Chen et al. 2020), the All-Sky Automated Survey (ASAS;

Pojmanski 2000, 2002; Pigulski et al. 2009), the All-Sky Automated Survey for Supernovae (ASAS-SN; Jayasinghe et al. 2019), LINEAR (Palaversa et al. 2013; Sesar et al. 2013), the Palomar Transient Factory (PTF; Sesar et al. 2014), the VISTA Variables in the Via Lactea survey (VVV; Contreras Ramos et al. 2018; Dékány et al. 2018), the fifth edition of the General Catalogue of Variable Stars (GCVS; Samus' et al. 2017), and the PanSTARRS1 $3\pi$ survey (PS1; Sesar et al. 2017). To integrate our compilation with known RR Lyrae stars in Galactic globular clusters (GCs), we used an updated version of the Variable Stars in Galactic Globular Clusters catalogue (Clement et al. 2001) as main reference, and for RR Lyrae stars in the MW UFDs, we used the compilation in Vivas et al. (2020). For the MW dSphs, we used the RR Lyrae collections by Muraveva et al. (2020) for Draco, Martínez-Vázquez et al. (2016) for Sculptor, Bersier & Wood (2002) for Fornax, Coppola et al. (2015) for Carina, Siegel & Majewski (2000) for Leo II, Stetson et al. (2014) for Leo I, Vivas et al. (2019) for Sextans, Kunder et al. (2008) for Sagittarius, and the collections by Nemec et al. (1988) and Bellazzini et al. (2002) for Ursa Minor.

We specifically note that in building our custom RR Lyrae catalogue, we gave preference to inclusiveness. We therefore did not make any cut for purity. For the selection procedures described in the following sections, we used a version frozen at December 2020 of our custom RR Lyrae catalogue. However, the catalogue is being regularly updated as soon as new RR Lyrae compilations appear in the literature, and we plan to make a most recently updated version available online after *Gaia* DR3 (Garofalo et al., in prep.).

We performed a spatial cross-match within a $2.5''$ paring radius of our custom RR Lyrae catalogue and sources in the *gaia_source* table of the *Gaia* EDR3 archive (*gaiaedr3.gaiasource*) and found a counterpart in the EDR3 main catalogue for 414 082 (97%) of the RR Lyrae stars in our collection<fnref n="3" />. The classifiers of the General Supervised Classification module in the variability analysis pipeline returned these 414 082 sources as RR Lyrae candidates with probabilities starting from very low values. More than 75% (311 798) were classified as RR Lyrae by the SOS Cep&RRL pipeline. Characteristic parameters (*P*, pulsation mode, etc.) consistent with the literature were recovered for about 65% of them.

### 3.2. Gold Sample and validation criteria

In order to validate the unexpectedly large number of candidate RR Lyrae produced by the classifiers and confirmed by the SOS Cep&RRL pipeline and to extract a bona fide sample to release in DR3, we adopted a strategy based on our custom

<footnote n="3">³ We refer to Gavras et al. (2023) for a comprehensive catalogue of known variable sources cross-matched with *Gaia* DR3. This also extends our catalogue to other types of variability.</footnote>
<figure><img src="image_5.png" /><figcaption>**Fig. 6.** Sky distributions in galactic coordinates (top panel) and equatorial coordinates (bottom panel) of 200 636 RR Lyrae stars in the Gold Sample.</figcaption></figure>

curves for DR3 RR Lyrae stars with different pulsation modes (RRab, RRc, and RRd) in the MW field and in a number of different stellar systems (the GCs M3 and M62, the LMC and the SMC, the Sculptor dSph, and the Phoenix II and Tucana II UFDs) are presented in Figs. 8 and 9.

The catalogue of 271 779 RR Lyrae stars was further cleaned from contaminants and sources affected by issues that emerged after the final export of the DR3 *variMETALLRYAE* table. This final cleaning procedure is described in Sect. 6.

# 4. RVS radial velocity time series for RR Lyrae stars and Cepheids

With DR3, epoch RVs measured from the RVS spectra are published for a small sample of RR Lyrae stars and Cepheids for the first time. This small dataset provides a first quality assessment of the RVS per-transit RVs. At the same time, it anticipates RVS data-products that will become available with next *Gaia* releases. In the following subsections we describe how this sample was selected (Sect. 4.1), was processed by the SOS pipeline (Sect. 4.2), and was validated with the literature (see Sect. 4.3 for the RR Lyrae stars, and Sect. 6.6 in Ripepi et al. 2023 for the Cepheids).

## 4.1. Target selection

The *gaia_source* table in the DR3 archive provides RV values<fnref n="4" /> for 5096 RR Lyrae stars and 3190 Cepheids that were confirmed

by the SOS Cep&RRL pipeline. From these, we selected sources with five or more epoch RV measurements and a mean *G* magnitude brighter than ~15.5 mag. A further selection was made by visual inspection of the light curves and RV curves, which produced a sample of 1100 RR Lyrae stars and 798 Cepheids.

The intensity-averaged *G* mean magnitudes (as computed by the SOS pipeline) of the 1 100 RR Lyrae stars lie in the range of 7.64 ≤ *G* ≤ 14.33 mag (Fig. 10, grey histogram), and the number of individual RVS measurements ranges from 5 to 77 (Fig. 11, grey histogram). The intensity-averaged *G* mean magnitudes of the 798 Cepheids lie in the range of 3.75 ≤ *G* ≤ 15.46 mag (Fig. 10, cyan histogram), and the number of valid RVS individual measurements ranges from 5 to 74 (Fig. 11, cyan histogram).

The epoch RVs were computed using the RVS pipeline described in the online documentation Sartoretti et al. (2022, Chap. 6). In practice, they were derived by comparing each cleaned and calibrated RVS spectrum with the synthetic reference template of a star with similar atmospheric parameters. See Sartoretti et al. (2022, Sect. 6.4.8) and Sartoretti et al. (2018, Sect. 7) for a detailed description of how epoch RVs are calculated, and Sartoretti et al. (2022, Fig. 6.13) for the median precision of epoch measurements as a function of *G*<sub>RVS</sub>. The quality of the epoch RVs depends on several factors: the *G*<sub>RVS</sub> magnitude of the star (because the fainter the star, the noisier the spectrum); the appropriate match with a synthetic reference template (see Sartoretti et al. 2022, Sect. 6.4.8.3 for how template spectra are associated with RVS spectra); the quality of astrometric data; and potential limitations of the processing software (e.g. for deblending or the identification of peculiar stars). The epoch RVs published in DR3 are only those of the 1100 RR Lyrae stars and 798 Cepheids described in this paper, which are available via the *Gaia* archive *vari_epoch_radialVelocity* table. Typical uncertainties of the epoch RVs for these sources are ≤1 km s⁻¹ for *G* ~ 9–9.5 mag (*G*<sub>RVS</sub> ~ 8.5–9 mag for RR Lyrae stars) and ≤6.5 km s⁻¹ for *G* ~ 13 mag (*G*<sub>RVS</sub> ~ 12.5 mag for

<footnote n="4">⁴ The RV values of RR Lyrae stars and Cepheids in the DR3 *gaia_source* table are combined RVs obtained in two different ways depending on the *G*<sub>RVS</sub> magnitude of the star. For bright stars (*G*<sub>RVS</sub> ≤ 12 mag), the combined RV is the median of the single-transit RVs. For faint stars, for which the single-transit RVs are less precise, the single-transit cross-correlation functions are averaged. The mean cross-correlation function obtained in this way is then used to measure the stellar RV.</footnote>
<figure><img src="image_6.png" /><figcaption>**Fig. 6.** Sky distributions in galactic coordinates (top panel) and equatorial coordinates (bottom panel) of 200 636 RR Lyrae stars in the Gold Sample.</figcaption></figure>

curves for DR3 RR Lyrae stars with different pulsation modes (RRab, RRc, and RRd) in the MW field and in a number of different stellar systems (the GCs M3 and M62, the LMC and the SMC, the Sculptor dSph, and the Phoenix II and Tucana II UFDs) are presented in Figs. 8 and 9.

The catalogue of 271 779 RR Lyrae stars was further cleaned from contaminants and sources affected by issues that emerged after the final export of the DR3 *variMETALLRYAE* table. This final cleaning procedure is described in Sect. 6.

# 4. RVS radial velocity time series for RR Lyrae stars and Cepheids

With DR3, epoch RVs measured from the RVS spectra are published for a small sample of RR Lyrae stars and Cepheids for the first time. This small dataset provides a first quality assessment of the RVS per-transit RVs. At the same time, it anticipates RVS data-products that will become available with next Gaia releases. In the following subsections we describe how this sample was selected (Sect. 4.1), was processed by the SOS pipeline (Sect. 4.2), and was validated with the literature (see Sect. 4.3 for the RR Lyrae stars, and Sect. 6.6 in Ripepi et al. 2023 for the Cepheids).

## 4.1. Target selection

The *gaia_source* table in the DR3 archive provides RV values<fnref n="4" /> for 5096 RR Lyrae stars and 3190 Cepheids that were confirmed

by the SOS Cep&RRL pipeline. From these, we selected sources with five or more epoch RV measurements and a mean *G* magnitude brighter than ~15.5 mag. A further selection was made by visual inspection of the light curves and RV curves, which produced a sample of 1100 RR Lyrae stars and 798 Cepheids.

The intensity-averaged *G* mean magnitudes (as computed by the SOS pipeline) of the 1 100 RR Lyrae stars lie in the range of 7.64 ≤ *G* ≤ 14.33 mag (Fig. 10, grey histogram), and the number of individual RVS measurements ranges from 5 to 77 (Fig. 11, grey histogram). The intensity-averaged *G* mean magnitudes of the 798 Cepheids lie in the range of 3.75 ≤ *G* ≤ 15.46 mag (Fig. 10, cyan histogram), and the number of valid RVS individual measurements ranges from 5 to 74 (Fig. 11, cyan histogram).

The epoch RVs were computed using the RVS pipeline described in the online documentation Sartoretti et al. (2022, Chap. 6). In practice, they were derived by comparing each cleaned and calibrated RVS spectrum with the synthetic reference template of a star with similar atmospheric parameters. See Sartoretti et al. (2022, Sect. 6.4.8) and Sartoretti et al. (2018, Sect. 7) for a detailed description of how epoch RVs are calculated, and Sartoretti et al. (2022, Fig. 6.13) for the median precision of epoch measurements as a function of *G*<sub>RVS</sub>. The quality of the epoch RVs depends on several factors: the *G*<sub>RVS</sub> magnitude of the star (because the fainter the star, the noisier the spectrum); the appropriate match with a synthetic reference template (see Sartoretti et al. 2022, Sect. 6.4.8.3 for how template spectra are associated with RVS spectra); the quality of astrometric data; and potential limitations of the processing software (e.g. for deblending or the identification of peculiar stars). The epoch RVs published in DR3 are only those of the 1100 RR Lyrae stars and 798 Cepheids described in this paper, which are available via the Gaia archive *vari_epoch_radialVelocity* table. Typical uncertainties of the epoch RVs for these sources are ≤1 km s⁻¹ for *G* ~ 9–9.5 mag (*G*<sub>RVS</sub> ~ 8.5–9 mag for RR Lyrae stars) and ≤6.5 km s⁻¹ for *G* ~ 13 mag (*G*<sub>RVS</sub> ~ 12.5 mag for

<footnote n="4">⁴ The RV values of RR Lyrae stars and Cepheids in the DR3 *gaia_source* table are combined RVs obtained in two different ways depending on the *G*<sub>RVS</sub> magnitude of the star. For bright stars (*G*<sub>RVS</sub> ≤ 12 mag), the combined RV is the median of the single-transit RVs. For faint stars, for which the single-transit RVs are less precise, the single-transit cross-correlation functions are averaged. The mean cross-correlation function obtained in this way is then used to measure the stellar RV.</footnote>
<figure><img src="image_6.png" /><figcaption>**Fig. 7.** PA, $\phi_{21}$ versus P and $\phi_{31}$ versus P diagrams of the 200 636 RR Lyrae stars in the Gold Sample. The 101 400 sources in common with OGLE are plotted using different colours for RRab (blue), RRc (magenta), and RRd (black) stars, respectively.</figcaption></figure>

RR Lyrae stars) (see Sartoretti et al. 2022, Fig. 6.13). The epoch data of all remaining stars will be published in DR4. The other RVS-pipeline products published in DR3 are at source level (i.e. obtained by combining data from all epochs). They are listed in Table 6.1 of the online documentation and are available via the Gaia archive gaia_source table. These products include, for example, information about the $G_{RVS}$ magnitude of the star (called grvs_mag in the Gaia archive) and the atmospheric parameters of the synthetic reference template used to derive the star epoch RVs (called rv_template_teff, rv_template_logg and rv_template_feh, and rv_atm_param_origin). Source-level RVS pipeline products are not also published for all the 1100 RR Lyrae stars and 798 Cepheids whose epoch RVs are published in DR3. Source-level information is lacking for 51 Cepheids and 45 RR Lyrae stars, for which the all-epoch-combined RV was deemed of insufficient quality (see Katz et al. 2023, for the filters applied to

the all-epoch-combined RVs). In most cases, the reason was the detection of potential variability, such as double lines in more than 10% of the epoch spectra, variability in spectral-sample flux from epoch to epoch, or a large dispersion in epoch RV ($radial\_velocity\_error > 40$ km s$^{-1}$). In other cases, the spectra were deemed too noisy, or the effective temperature $T_{eff}$ was found to exceed the limit for good-quality RV measurements (i.e. 7000 K for $G_{RVS} > 12$ mag and 14 500 K for $G_{RVS} \le 12$ mag). However, we note that most of the above issues are normal features for high-amplitude variable sources such as RR Lyrae stars and Cepheids, whose RV curves typically exhibit amplitudes of tens of km s$^{-1}$. We carefully inspected the RV curves of these 51 Cepheids and 45 RR-Lyrae stars, and none of them was found to have a peculiar shape. In contrast, the large majority of these sources have very regular and well defined RV curves. Therefore, we kept them for publication, and in Appendix A.1, we provide information about their $G_{RVS}$ magnitudes and the atmospheric parameters of the associated templates. We also explain why no source-level RVS pipeline products are published for them.

## 4.2. Processing of the RV data through the SOS Cep&RRL pipeline, and results

The time-series RV data of the 1100 RR Lyrae stars and 798 Cepheids were processed by the SOS Cep&RRL pipeline. For sources with more than seven transits (1097 out of 1100 RR Lyrae stars and 785 out of 798 Cepheids), the RV curves obtained by folding the data with the periods inferred from the G-band photometry were modelled with truncated Fourier functions. The mean RV ($\langle RV \rangle$), the peak-to-peak RV amplitude [Amp(RV)], and the epoch of minimum RV were computed from the modelled RV curves and are published in the DR3 vari_errlyrae and vari-cepheid tables. From top to bottom, Fig. 12 shows examples of $G_{BP}$, G, and $G_{RP}$ light curves and RV curves for RR Lyrae stars that are released in DR3. The RV curves have the typical specular shape with respect to the light curves for which the minimum value in RV corresponds to the maximum stellar brightness.

An atlas of the light and RV curves for the full sample of 1100 RR Lyrae stars whose time-series RVs are published in DR3 is presented in Appendix A.3. Examples of RV curves and an atlas of the light curves and RV curves for the 798 Cepheids are presented in Ripepi et al. (2023).

Figure 13 shows the error distribution of the mean RV values computed with the SOS pipeline ($\sigma\langle RV \rangle$) for the 1097/1100 RR Lyrae stars, whereas Fig. 14 shows $\sigma\langle RV \rangle$ as a function of the mean G magnitude of these sources. The uncertainty ranges from 0.48 km s$^{-1}$ to 84.88 km s$^{-1}$ for $\langle G \rangle$ ranging from 7.64 to 14.30 mag, with a peak between 3 and 6 km s$^{-1}$. This peak corresponds to the bulk of RR Lyrae stars that have a mean G magnitude between 12 and 13 mag in Fig. 14 and is consistent with Fig. 6.13 in Sartoretti et al. (2022). Fewer than 20 sources have $\sigma_{\langle RV \rangle} > 25$ km s$^{-1}$. They correspond to sources in the faint magnitude tail of Fig. 14.

Finally, Fig. 15 shows the P versus Amp(RV) diagram of the 1097 RR Lyrae stars. A few sources have very high Amp(RV) values. Three of them are contaminants (filled green circles), and the others have very few RV measurements and hence very uncertain Amp(RV) values.

A comparison was made of the SOS mean RV values of the 1097 RR Lyrae stars and the combined RV values for these stars in the Gaia DR3 gaia_source table. The two RV values are available for 1054 RR Lyrae stars. This comparison is shown in
<figure><img src="image_7.png" /><figcaption>**Fig. 7.** PA, $\phi_{21}$ versus P and $\phi_{31}$ versus P diagrams of the 200 636 RR Lyrae stars in the Gold Sample. The 101 400 sources in common with OGLE are plotted using different colours for RRab (blue), RRc (magenta), and RRd (black) stars, respectively.</figcaption></figure>

RR Lyrae stars) (see Sartoretti et al. 2022, Fig. 6.13). The epoch data of all remaining stars will be published in DR4. The other RVS-pipeline products published in DR3 are at source level (i.e. obtained by combining data from all epochs). They are listed in Table 6.1 of the online documentation and are available via the Gaia archive gaia_source table. These products include, for example, information about the $G_{RVS}$ magnitude of the star (called grvs_mag in the Gaia archive) and the atmospheric parameters of the synthetic reference template used to derive the star epoch RVs (called rv_template_teff, rv_template_logg and rv_template_feh, and rv_atm_param_origin). Source-level RVS pipeline products are not also published for all the 1100 RR Lyrae stars and 798 Cepheids whose epoch RVs are published in DR3. Source-level information is lacking for 51 Cepheids and 45 RR Lyrae stars, for which the all-epoch-combined RV was deemed of insufficient quality (see Katz et al. 2023, for the filters applied to

the all-epoch-combined RVs). In most cases, the reason was the detection of potential variability, such as double lines in more than 10% of the epoch spectra, variability in spectral-sample flux from epoch to epoch, or a large dispersion in epoch RV ($radial\_velocity\_error > 40$ km s$^{-1}$). In other cases, the spectra were deemed too noisy, or the effective temperature $T_{eff}$ was found to exceed the limit for good-quality RV measurements (i.e. 7000 K for $G_{RVS} > 12$ mag and 14 500 K for $G_{RVS} \le 12$ mag). However, we note that most of the above issues are normal features for high-amplitude variable sources such as RR Lyrae stars and Cepheids, whose RV curves typically exhibit amplitudes of tens of km s$^{-1}$. We carefully inspected the RV curves of these 51 Cepheids and 45 RR-Lyrae stars, and none of them was found to have a peculiar shape. In contrast, the large majority of these sources have very regular and well defined RV curves. Therefore, we kept them for publication, and in Appendix A.1, we provide information about their $G_{RVS}$ magnitudes and the atmospheric parameters of the associated templates. We also explain why no source-level RVS pipeline products are published for them.

## 4.2. Processing of the RV data through the SOS Cep&RRL pipeline, and results

The time-series RV data of the 1100 RR Lyrae stars and 798 Cepheids were processed by the SOS Cep&RRL pipeline. For sources with more than seven transits (1097 out of 1100 RR Lyrae stars and 785 out of 798 Cepheids), the RV curves obtained by folding the data with the periods inferred from the G-band photometry were modelled with truncated Fourier functions. The mean RV ($\langle RV \rangle$), the peak-to-peak RV amplitude [Amp(RV)], and the epoch of minimum RV were computed from the modelled RV curves and are published in the DR3 vari_rrlyrae and vari-cepheid tables. From top to bottom, Fig. 12 shows examples of $G_{BP}$, G, and $G_{RP}$ light curves and RV curves for RR Lyrae stars that are released in DR3. The RV curves have the typical specular shape with respect to the light curves for which the minimum value in RV corresponds to the maximum stellar brightness.

An atlas of the light and RV curves for the full sample of 1100 RR Lyrae stars whose time-series RVs are published in DR3 is presented in Appendix A.3. Examples of RV curves and an atlas of the light curves and RV curves for the 798 Cepheids are presented in Ripepi et al. (2023).

Figure 13 shows the error distribution of the mean RV values computed with the SOS pipeline ($\sigma\langle RV \rangle$) for the 1097/1100 RR Lyrae stars, whereas Fig. 14 shows $\sigma\langle RV \rangle$ as a function of the mean G magnitude of these sources. The uncertainty ranges from 0.48 km s$^{-1}$ to 84.88 km s$^{-1}$ for $\langle G \rangle$ ranging from 7.64 to 14.30 mag, with a peak between 3 and 6 km s$^{-1}$. This peak corresponds to the bulk of RR Lyrae stars that have a mean G magnitude between 12 and 13 mag in Fig. 14 and is consistent with Fig. 6.13 in Sartoretti et al. (2022). Fewer than 20 sources have $\sigma_{\langle RV \rangle} > 25$ km s$^{-1}$. They correspond to sources in the faint magnitude tail of Fig. 14.

Finally, Fig. 15 shows the P versus Amp(RV) diagram of the 1097 RR Lyrae stars. A few sources have very high Amp(RV) values. Three of them are contaminants (filled green circles), and the others have very few RV measurements and hence very uncertain Amp(RV) values.

A comparison was made of the SOS mean RV values of the 1097 RR Lyrae stars and the combined RV values for these stars in the Gaia DR3 gaia_source table. The two RV values are available for 1054 RR Lyrae stars. This comparison is shown in
<figure><img src="image_7.png" /><figcaption>**Fig. 8.** Examples of light curves for SOS-confirmed DR3 RR Lyrae stars in the globular clusters M3 and M62, in the LMC and the SMC, and a new all-sky RR Lyrae star.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 9.** Same as in Fig. 8, but for RR Lyrae stars in the Sculptor dSph galaxy and in the Phoenix II and Tucana II MW UFDs. Only the G-band light curves are shown because the S/N of the $G_{BP}$ and $G_{RP}$ time-series data is poor at the faint magnitudes of the RR Lyrae stars in these systems.</figcaption></figure>

Fig. 16. The agreement within the errors of the two sets of RV measurements is good.

The median and mean difference of the two average values is 5.21 and 6.88 km s⁻¹ (with 6.35 km s⁻¹ standard deviation), respectively. Finally, Fig. 17 shows the RV map defined by 1097 out of 1100 RR Lyrae stars in the DR3 *vari_rrlyrae* (righ panel), and in the left panel, the map defined by the 5096 RR Lyrae stars in the DR3 *gaia_source* table, for comparison. The sources are colour-coded according their mean RV val-

<figure><img src="image_9.png" /><figcaption>**Fig. 10.** G magnitude distribution of the 1100 RR Lyrae stars (grey histogram) and 798 Cepheids (cyan histogram) whose RV time series are published in Gaia DR3.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Fig. 11.** Number of available individual measurements in the RV time-series data for the 1100 RR Lyrae stars (grey histogram) and 798 Cepheids (cyan histogram) subsamples.</figcaption></figure>

ues. The two distributions are very well consistent, as expected from the good agreement between the two sets of RV values (see Fig. 16). RR Lyrae stars are distributed at all galactic latitudes and populate the maps with RVs ranging from high negative to high positive values.
<figure><img src="image_8.png" /><figcaption>**Fig. 8.** Examples of light curves for SOS-confirmed DR3 RR Lyrae stars in the globular clusters M3 and M62, in the LMC and the SMC, and a new all-sky RR Lyrae star.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Fig. 9.** Same as in Fig. 8, but for RR Lyrae stars in the Sculptor dSph galaxy and in the Phoenix II and Tucana II MW UFDs. Only the G-band light curves are shown because the S/N of the $G_{BP}$ and $G_{RP}$ time-series data is poor at the faint magnitudes of the RR Lyrae stars in these systems.</figcaption></figure>

Fig. 16. The agreement within the errors of the two sets of RV measurements is good.

The median and mean difference of the two average values is 5.21 and 6.88 km s⁻¹ (with 6.35 km s⁻¹ standard deviation), respectively. Finally, Fig. 17 shows the RV map defined by 1097 out of 1100 RR Lyrae stars in the DR3 *vari_rrlyrae* (righ panel), and in the left panel, the map defined by the 5096 RR Lyrae stars in the DR3 *gaia_source* table, for comparison. The sources are colour-coded according their mean RV val-

<figure><img src="image_10.png" /><figcaption>**Fig. 10.** G magnitude distribution of the 1100 RR Lyrae stars (grey histogram) and 798 Cepheids (cyan histogram) whose RV time series are published in Gaia DR3.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Fig. 11.** Number of available individual measurements in the RV time-series data for the 1100 RR Lyrae stars (grey histogram) and 798 Cepheids (cyan histogram) subsamples.</figcaption></figure>

ues. The two distributions are very well consistent, as expected from the good agreement between the two sets of RV values (see Fig. 16). RR Lyrae stars are distributed at all galactic latitudes and populate the maps with RVs ranging from high negative to high positive values.
<figure><img src="image_11.png" /><figcaption>**Fig. 12.** Examples of light curves and RV curves for RR Lyrae stars released in DR3. From top to bottom in each panel, we show $G_{BP}$, $G$, and $G_{RP}$ light curves and RV curve. The error bars of the photometric and RV measurements are smaller than or comparable to the symbol size. In the upper row from left to right, the sources are a first-overtone (RRc) and a double-mode (RRd) star; in the lower row, we show two fundamental-mode (RRab) RR Lyrae stars.</figcaption></figure>

### 4.3. Validation with the literature

A number of RR Lyrae stars and Cepheids for which epoch RVs are published in DR3 were analysed in the past with the Baade-Wesselink (B-W) technique (e.g. Cacciari et al. 1992, and references therein, for different versions of the B-W method applied to RR Lyrae stars, and Gieren & Barnes 1989; Ripepi et al. 1997, for B-W analyses of Cepheids). Hence, high-accuracy RV measurements either obtained with the CORAVEL spectrophotometer (Baranne et al. 1979) or from high-resolution spectra are available in the literature for these stars. We selected 19 RR Lyrae stars with 10 or more epoch RVS measurements in the RV curves and have made a detailed comparison with the high-accuracy RVs covering the whole stellar pulsation cycle

that are available for these variable stars in the literature. We mainly used data taken from the most recent literature for our comparison, as datasets collected in/before the early eighties often have very large uncertainties. A similar comparison for a sample of DCEPs is presented in Ripepi et al. (2023).

The 19 RR Lyrae stars used for this test are listed in Table A.3. In the table we indicate the literature data we used for the comparison, the mean astrophysical stellar parameters (⟨$T_{eff}$⟩, ⟨log g⟩, and iron abundance: [Fe/H]), which in general are the values that are adopted for or derived from the B-W analyses. The sample comprises 17 RRab and 2 RRc stars. They span a range in [Fe/H] of more than 2 dex. Three of them are known or suspected to be affected by Blažko effect (Blažko 1907), a periodic modulation of the amplitude and shape of the light (and
<figure><img src="image_12.png" /><figcaption>**Fig. 12.** Examples of light curves and RV curves for RR Lyrae stars released in DR3. From top to bottom in each panel, we show $G_{BP}$, $G$, and $G_{RP}$ light curves and RV curve. The error bars of the photometric and RV measurements are smaller than or comparable to the symbol size. In the upper row from left to right, the sources are a first-overtone (RRc) and a double-mode (RRd) star; in the lower row, we show two fundamental-mode (RRab) RR Lyrae stars.</figcaption></figure>

### 4.3. Validation with the literature

A number of RR Lyrae stars and Cepheids for which epoch RVs are published in DR3 were analysed in the past with the Baade-Wesselink (B-W) technique (e.g. Cacciari et al. 1992, and references therein, for different versions of the B-W method applied to RR Lyrae stars, and Gieren & Barnes 1989; Ripepi et al. 1997, for B-W analyses of Cepheids). Hence, high-accuracy RV measurements either obtained with the CORAVEL spectrophotometer (Baranne et al. 1979) or from high-resolution spectra are available in the literature for these stars. We selected 19 RR Lyrae stars with 10 or more epoch RVS measurements in the RV curves and have made a detailed comparison with the high-accuracy RVs covering the whole stellar pulsation cycle

that are available for these variable stars in the literature. We mainly used data taken from the most recent literature for our comparison, as datasets collected in/before the early eighties often have very large uncertainties. A similar comparison for a sample of DCEPs is presented in Ripepi et al. (2023).

The 19 RR Lyrae stars used for this test are listed in Table A.3. In the table we indicate the literature data we used for the comparison, the mean astrophysical stellar parameters ($\langle T_{eff} \rangle$, $\langle \log g \rangle$, and iron abundance: [Fe/H]), which in general are the values that are adopted for or derived from the B-W analyses. The sample comprises 17 RRab and 2 RRc stars. They span a range in [Fe/H] of more than 2 dex. Three of them are known or suspected to be affected by Blažko effect (Blažko 1907), a periodic modulation of the amplitude and shape of the light (and
<figure><img src="image_12.png" /><figcaption>**Fig. 13.** Error distribution of the mean RV values computed with the SOS pipeline for 1097 out of 1100 RR Lyrae stars.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Fig. 14.** Uncertainty of the mean RV values as a function of the SOS mean $\langle G \rangle$ magnitude for 1097 out of 1100 RR Lyrae stars (filled grey points). We plot in different colours one DCEP (red symbol) and three ECLs (green symbols) that contaminate the 1097 RR Lyrae sample (see Sect. 6 for details).</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>**Fig. 15.** *P* vs. Amp(RV) diagram of 1097 out of 1100 RR Lyrae stars. Symbols and colour-coding are the same as in Fig. 14. The filled blue points show 19 RR Lyrae stars with high-accuracy RV curves in the literature that were used to validate the *Gaia* RVs (see Sect. 4.3).</figcaption></figure>

RV) curve, occurring with periodicities from tens to hundreds of days; one (V32) is a member of a globular cluster (NGC 6121–M4), and UU Vir is an RR Lyrae star suspected to be in a binary system, according to anomaly detected in the *Gaia* DR2 proper motions for the source (Kervella et al. 2019). The 19 RR Lyrae stars have $0.273 \le P \le 0.660$ d, $9.56 \le \langle G \rangle \le 12.90$ mag, and 10 or more (up to 37) individual RVS measurements, with errors in the range from 0.41 to $16 \text{ km s}^{-1}$ depending on the magnitude and pulsation phase.

<figure><img src="image_15.png" /><figcaption>**Fig. 16.** Comparison of the mean RV values in the DR3 *vari_errlyrae* table, which are computed with the SOS Cep&RRL pipeline from the modelled RV curves of the RR Lyrae stars, and the combined RV values in the DR3 *gaia_source* table for the 1054 RR Lyrae stars for which both values are available. The median and mean difference between the two average values is 5.21 and 6.88 km s⁻¹ (with a standard deviation of 6.35 km s⁻¹), respectively.</figcaption></figure>

The RVS measurements of these 19 RR Lyrae stars are reasonably well distributed over the pulsation cycle. More than one RV dataset is often available in the literature to make the comparison.

The literature RVs and the *Gaia* RVS measurements of the stars in Table A.3 span time intervals of up to a few decades, and the literature periods often do not allow an optimal phasing of all the available RV datasets. We therefore performed a new period search on each combined (literature plus *Gaia*) RV dataset with the package Graphical Analyzer of Time Series (GRATIS; custom software developed at the Bologna Observatory by P. Montegriffo, see e.g. Clementini et al. 2000) and defined periods that allowed us to optimally match the *Gaia* and the literature RV curves for all sources used for this comparison<fnref n="5" />. No photometry was involved in the procedure, but we note that the differences between the periods derived for the 19 RR Lyrae stars from the combined RV datasets ($P_{RV}$) and the periods derived by the SOS pipeline ($P_{SOS}$) from the DR3 time-series photometry are in the range of $2.8 \times 10^{-8}$ d $< |P_{RV} - P_{SOS}| < 2.0 \times 10^{-5}$ d for 18 of the 19 stars in our sample. Only for V440 Sgr (source_id=6771307454464848768) is $P_{SOS}$ 0.048 d shorter than the period derived from the combined RV dataset, and it is clearly incorrect because this star has only sparsely sampled light curves and RV curves. The correct period for V440 Sgr is provided in Table A.3.

As an example, Fig. 18 shows the radial velocity curves of the RRc star YZ Cap and the RRab stars RS Boo, W Crt, RR Cet, V32 in M4, and W Tuc using different colours for the literature and the *Gaia* RVS data. The RV curves of the remaining 13 RR Lyrae stars are presented in Fig. A.1. This comparison shows that the shape and amplitude of the *Gaia* RVS and the literature RV curves agree well for 14 of the 19 RR Lyrae stars in the sample, which shows the good quality of the RVS epoch RV data for these sources. Specifically, the agreement is good for YZ Cap, RS Boo, W Tuc, V Ind, DX Del, UU Cet V440 Sgr, and also for V32 in M4, TV Boo, AV Peg, TW Her, and UU Vir when their RVS curves are rigidly shifted by +5 km s⁻¹ for the first two, −3 km s⁻¹ for the third source, and by −4 km s⁻¹ for the last two sources so that the literature curves are better matched.

<footnote n="5">⁵ As far as we know, none of the 19 RR Lyrae stars considered for our comparison is known to present significant period changes. The period of some of these RR Lyrae stars is known to be fairly constant.</footnote>
<figure><img src="image_13.png" /><figcaption>**Fig. 13.** Error distribution of the mean RV values computed with the SOS pipeline for 1097 out of 1100 RR Lyrae stars.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>**Fig. 14.** Uncertainty of the mean RV values as a function of the SOS mean $\langle G \rangle$ magnitude for 1097 out of 1100 RR Lyrae stars (filled grey points). We plot in different colours one DCEP (red symbol) and three ECLs (green symbols) that contaminate the 1097 RR Lyrae sample (see Sect. 6 for details).</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>**Fig. 15.** *P* vs. Amp(RV) diagram of 1097 out of 1100 RR Lyrae stars. Symbols and colour-coding are the same as in Fig. 14. The filled blue points show 19 RR Lyrae stars with high-accuracy RV curves in the literature that were used to validate the *Gaia* RVs (see Sect. 4.3).</figcaption></figure>

RV) curve, occurring with periodicities from tens to hundreds of days; one (V32) is a member of a globular cluster (NGC 6121–M4), and UU Vir is an RR Lyrae star suspected to be in a binary system, according to anomaly detected in the *Gaia* DR2 proper motions for the source (Kervella et al. 2019). The 19 RR Lyrae stars have $0.273 \le P \le 0.660$ d, $9.56 \le \langle G \rangle \le 12.90$ mag, and 10 or more (up to 37) individual RVS measurements, with errors in the range from 0.41 to $16 \text{ km s}^{-1}$ depending on the magnitude and pulsation phase.

<figure><img src="image_16.png" /><figcaption>**Fig. 16.** Comparison of the mean RV values in the DR3 *vari_-rrlyrae* table, which are computed with the SOS Cep&RRL pipeline from the modelled RV curves of the RR Lyrae stars, and the combined RV values in the DR3 *gaia_source* table for the 1054 RR Lyrae stars for which both values are available. The median and mean difference between the two average values is 5.21 and 6.88 km s⁻¹ (with a standard deviation of 6.35 km s⁻¹), respectively.</figcaption></figure>

The RVS measurements of these 19 RR Lyrae stars are reasonably well distributed over the pulsation cycle. More than one RV dataset is often available in the literature to make the comparison.

The literature RVs and the *Gaia* RVS measurements of the stars in Table A.3 span time intervals of up to a few decades, and the literature periods often do not allow an optimal phasing of all the available RV datasets. We therefore performed a new period search on each combined (literature plus *Gaia*) RV dataset with the package Graphical Analyzer of Time Series (GRATIS; custom software developed at the Bologna Observatory by P. Montegriffo, see e.g. Clementini et al. 2000) and defined periods that allowed us to optimally match the *Gaia* and the literature RV curves for all sources used for this comparison<fnref n="5" />. No photometry was involved in the procedure, but we note that the differences between the periods derived for the 19 RR Lyrae stars from the combined RV datasets ($P_{RV}$) and the periods derived by the SOS pipeline ($P_{SOS}$) from the DR3 time-series photometry are in the range of $2.8 \times 10^{-8}$ d $< |P_{RV} - P_{SOS}| < 2.0 \times 10^{-5}$ d for 18 of the 19 stars in our sample. Only for V440 Sgr (source_id=6771307454464848768) is $P_{SOS}$ 0.048 d shorter than the period derived from the combined RV dataset, and it is clearly incorrect because this star has only sparsely sampled light curves and RV curves. The correct period for V440 Sgr is provided in Table A.3.

As an example, Fig. 18 shows the radial velocity curves of the RRc star YZ Cap and the RRab stars RS Boo, W Crt, RR Cet, V32 in M4, and W Tuc using different colours for the literature and the *Gaia* RVS data. The RV curves of the remaining 13 RR Lyrae stars are presented in Fig. A.1. This comparison shows that the shape and amplitude of the *Gaia* RVS and the literature RV curves agree well for 14 of the 19 RR Lyrae stars in the sample, which shows the good quality of the RVS epoch RV data for these sources. Specifically, the agreement is good for YZ Cap, RS Boo, W Tuc, V Ind, DX Del, UU Cet V440 Sgr, and also for V32 in M4, TV Boo, AV Peg, TW Her, and UU Vir when their RVS curves are rigidly shifted by +5 km s⁻¹ for the first two, -3 km s⁻¹ for the third source, and by -4 km s⁻¹ for the last two sources so that the literature curves are better matched.

<footnote n="5">⁵ As far as we know, none of the 19 RR Lyrae stars considered for our comparison is known to present significant period changes. The period of some of these RR Lyrae stars is known to be fairly constant.</footnote>
<figure><img src="image_16.png" /><figcaption>**Fig. 17.** Radial velocity maps defined by 1097 out of 1100 RR Lyrae stars in the DR3 *vari_-rrlyrae* (righ panel) and 5096 RR Lyrae stars in the *gaia_source* table (left panel). The sources are colour-coded according to their mean RV values, as encoded in the colour bar on the right.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>**Fig. 18.** Comparison of the *Gaia* RVS radial velocities (filled blue circles) with literature RV datasets (filled magenta and cyan circles) for the RRc star YZ Cap (top left) and the RRab stars RS Boo (middle left), W Crt (bottom left), RR Cet (top right), V32 in the GC M4 (middle right), and W Tuc (bottom right). We also show the pulsation period (as rederived in our analysis) and the intensity-averaged *G*-band mean magnitude (as derived by the SOS Cep&RRL pipeline). The *Gaia* RV curve of V32 in M4 was shifted by −5 km s⁻¹ to better match the literature RV curve.</figcaption></figure>

The agreement is also acceptable for RV Phe and SS For, despite the large scatter caused by the Blazhko effect in these two stars. Conversely, there are noticeable differences between the literature and *Gaia* RV curves for RR Cet, RX Eri, SU Dra, SW Dra, and to a lesser extent, also for W Crt. These differences are most apparent around the bump just before the RV maxima, around phases 0.7–0.9, where the *Gaia* RVS curves reach higher velocities than the literature curves. Investigating the reason for these differences is beyond the purposes of this paper,

but we note that shock waves are known to propagate in the atmosphere of RR Lyrae stars in correspondence with the hump (phase ~0.9) and bump (phase ~0.7) in the light and RV curves (Gillet & Crowe 1988; Clementini et al. 1994; Gillet & Fokin 2014, and references therein) that cause flux redistribution, H line emission, and U-excess. The RVS measurements seem to reflect the flux redistribution caused by shocks propagating in the atmospheres of these 5 RR Lyrae stars better than the literature RVs.
<figure><img src="image_17.png" /><figcaption>**Fig. 17.** Radial velocity maps defined by 1097 out of 1100 RR Lyrae stars in the DR3 *vari_-rrlyrae* (righ panel) and 5096 RR Lyrae stars in the *gaia_source* table (left panel). The sources are colour-coded according to their mean RV values, as encoded in the colour bar on the right.</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>**Fig. 18.** Comparison of the *Gaia* RVS radial velocities (filled blue circles) with literature RV datasets (filled magenta and cyan circles) for the RRc star YZ Cap (top left) and the RRab stars RS Boo (middle left), W Crt (bottom left), RR Cet (top right), V32 in the GC M4 (middle right), and W Tuc (bottom right). We also show the pulsation period (as rederived in our analysis) and the intensity-averaged *G*-band mean magnitude (as derived by the SOS Cep&RRL pipeline). The *Gaia* RV curve of V32 in M4 was shifted by −5 km s⁻¹ to better match the literature RV curve.</figcaption></figure>

The agreement is also acceptable for RV Phe and SS For, despite the large scatter caused by the Blazhko effect in these two stars. Conversely, there are noticeable differences between the literature and *Gaia* RV curves for RR Cet, RX Eri, SU Dra, SW Dra, and to a lesser extent, also for W Crt. These differences are most apparent around the bump just before the RV maxima, around phases 0.7–0.9, where the *Gaia* RVS curves reach higher velocities than the literature curves. Investigating the reason for these differences is beyond the purposes of this paper,

but we note that shock waves are known to propagate in the atmosphere of RR Lyrae stars in correspondence with the hump (phase ~0.9) and bump (phase ~0.7) in the light and RV curves (Gillet & Crowe 1988; Clementini et al. 1994; Gillet & Fokin 2014, and references therein) that cause flux redistribution, H line emission, and U-excess. The RVS measurements seem to reflect the flux redistribution caused by shocks propagating in the atmospheres of these 5 RR Lyrae stars better than the literature RVs.
# 5. Astrophysical parameters

The StellarParametersDerivation module of the SOS Cep&RRL pipeline (see Fig. 2) computes two main astrophysical parameters for the confirmed RR Lyrae stars: 1. a photometric estimate of individual metal abundance ([Fe/H]) for RRab and RRc stars whose light curves have been Fourier-modelled with at least three harmonics, and 2. a G-band absorption [A(G)] for RRab stars for which the (G - G<sub>RP</sub>) colour is available. The StellarParametersDerivation module is fully described in Sect. 2.1 of Paper II. Here, we only note that unlike in DR2, uncertainties in metallicity and A(G) values (as well as for any other parameter derived by the SOS pipeline) in DR3 were calculated with the bootstrap method.

In the following, we present the [Fe/H] abundances (Sect. 5.1) and A(G) values (Sect. 5.3) computed from the pulsation characteristics of the confirmed RR Lyrae stars, and compare them with values in the literature and with the astrophysical parameters derived by the Gaia pipeline that processes the RVS spectra and the BP, RP low-resolution prism spectra (Apsis; Creevey et al. 2023; Sects. 5.2 and 5.4).

## 5.1. Metallicity

In the Gaia DR3 vari RRlyrae table, individual photometric metallicities ([Fe/H]) are published for 133 557 RR Lyrae stars. They were computed by the StellarParametersDerivation module from the pulsation period *P* and the *φ*<sub>31</sub> parameter of the *G* light-curve Fourier decomposition, using the relations for RRab and RRc stars derived in Nemec et al. (2013). These relations are calibrated on [Fe/H] values obtained from an abundance analysis of high-resolution spectra (R ~ 36 000 and 65 000) of 41 field RR Lyrae stars.

Figure 19 shows the error distribution of the photometric metallicities for the 133 557 RR Lyrae in the sample.

Mean and median metallicity errors are 0.46 dex (with 0.33 dex std) and 0.36 dex, respectively. Errors were computed by adding the uncertainty estimated with the bootstrap method and the scatter around the calibration relations of 0.084 dex and 0.13 dex for RRab and RRc stars, respectively (Nemec et al. 2013), in quadrature and by adopting a rather generous systematic error of 0.2 dex that likely led to an overestimation of the metallicity uncertainties.

To validate the photometric metallicities, we first determined how well they reproduce the metal abundance of the Nemec et al. (2013) calibrators. This is shown in Fig. 20, where the [Fe/H] metallicities derived by the SOS Cep&RRL pipeline are compared with the metal abundances from high-resolution spectra of 39 RR Lyrae of the Nemec et al. (2013) calibrators for which both estimates are available. The agreement is good within the errors, confirming that the SOS photometric metallicities of RR Lyrae stars are closely tied to the metallicity scale from the abundance analysis of Nemec et al. (2013). We note, however, that the photometric metallicity of RR Lyr, the prototype and brightest star of the class, is significantly discrepant and poorly determined, as shown by the very large error bars. The reason likely is a poor determination of the *φ*<sub>31</sub> parameter for the star.

As already noted in Paper I, the photometric metallicities inferred from the [Fe/H], *P*, and *φ*<sub>31</sub> relation better represent the mean metal abundance of a population of RR Lyrae stars than the metallicity of the individual sources. Furthermore, new calibrations of this relation have appeared in the recent literature

<figure><img src="image_18.png" /><figcaption>**Fig. 19.** Error distribution of the metallicities derived for 133 557 DR3 RR Lyrae stars by the SOS pipeline. The mean and median metallicity errors are 0.46 dex (0.33 dex std) and 0.36 dex, respectively. We show only sources with $\sigma_{[Fe/H]} \le 2.0$ dex (i.e. 99.6% of the sample). We also note that for 71% of the sources in the plot, $\sigma_{[Fe/H]} \le 0.5$ dex.</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>**Fig. 20.** Comparison of the photometric metallicities derived by the SOS Cep&RRL pipeline and the metallicities from high-resolution spectra of 39 RR Lyrae stars of the Nemec et al. (2013) calibrators.</figcaption></figure>

(e.g. Iorio & Belokurov 2021; Mullen et al. 2021)<fnref n="6" />. Claims have been made by Iorio & Belokurov (2021) that metallicities based on the Nemec et al. (2013) calibrations are biased toward high metallicities. Conversely, Mullen et al. (2021) found an excellent agreement for higher metallicities in the Nemec et al. (2013) calibration range (−1.5 ≲ [Fe/H] ≲ 0.03 dex), while estimates diverge for lower metallicities.

In order to test the reliability of the RR Lyrae metallicities computed with the SOS pipeline, we compared them with the metal abundances from high-resolution spectroscopy available in the literature for different samples of RR Lyrae stars. Because the Mullen et al. (2021) relations are calibrated on the RR Lyrae metallicities from high-resolution spectra (R ~ 35 000) of Crestani et al. (2021), we discuss the comparison with Crestani et al. (2021) in the following. A comparison with other abundance analyses of RR Lyrae stars in the literature is presented in Appendix B.1.

First we compared the metal abundances from high-resolution spectra for RR Lyrae stars in common between Nemec et al. (2013) and Crestani et al. (2021). This comparison is shown in the left panel of Fig. 21 and seems to confirm that the Nemec et al. (2013) metallicities may be 0.1–0.2 dex higher than those of Crestani et al. (2021) for [Fe/H] ~ −1.5 dex.

<footnote n="6">⁶ We recall that the pipelines processing the Gaia data are frozen well in advance of releases. Specifically, the SOS Cep&RRL pipeline adopted to process the DR3 data was frozen in early 2020.</footnote>
# 5. Astrophysical parameters

The StellarParametersDerivation module of the SOS Cep&RRL pipeline (see Fig. 2) computes two main astrophysical parameters for the confirmed RR Lyrae stars: 1. a photometric estimate of individual metal abundance ([Fe/H]) for RRab and RRc stars whose light curves have been Fourier-modelled with at least three harmonics, and 2. a G-band absorption [A(G)] for RRab stars for which the (G − G<sub>RP</sub>) colour is available. The StellarParametersDerivation module is fully described in Sect. 2.1 of Paper II. Here, we only note that unlike in DR2, uncertainties in metallicity and A(G) values (as well as for any other parameter derived by the SOS pipeline) in DR3 were calculated with the bootstrap method.

In the following, we present the [Fe/H] abundances (Sect. 5.1) and A(G) values (Sect. 5.3) computed from the pulsation characteristics of the confirmed RR Lyrae stars, and compare them with values in the literature and with the astrophysical parameters derived by the Gaia pipeline that processes the RVS spectra and the BP, RP low-resolution prism spectra (Apsis; Creevey et al. 2023; Sects. 5.2 and 5.4).

## 5.1. Metallicity

In the Gaia DR3 vari RRlyrae table, individual photometric metallicities ([Fe/H]) are published for 133 557 RR Lyrae stars. They were computed by the StellarParametersDerivation module from the pulsation period *P* and the *φ*<sub>31</sub> parameter of the *G* light-curve Fourier decomposition, using the relations for RRab and RRc stars derived in Nemec et al. (2013). These relations are calibrated on [Fe/H] values obtained from an abundance analysis of high-resolution spectra (R ~ 36 000 and 65 000) of 41 field RR Lyrae stars.

Figure 19 shows the error distribution of the photometric metallicities for the 133 557 RR Lyrae in the sample.

Mean and median metallicity errors are 0.46 dex (with 0.33 dex std) and 0.36 dex, respectively. Errors were computed by adding the uncertainty estimated with the bootstrap method and the scatter around the calibration relations of 0.084 dex and 0.13 dex for RRab and RRc stars, respectively (Nemec et al. 2013), in quadrature and by adopting a rather generous systematic error of 0.2 dex that likely led to an overestimation of the metallicity uncertainties.

To validate the photometric metallicities, we first determined how well they reproduce the metal abundance of the Nemec et al. (2013) calibrators. This is shown in Fig. 20, where the [Fe/H] metallicities derived by the SOS Cep&RRL pipeline are compared with the metal abundances from high-resolution spectra of 39 RR Lyrae of the Nemec et al. (2013) calibrators for which both estimates are available. The agreement is good within the errors, confirming that the SOS photometric metallicities of RR Lyrae stars are closely tied to the metallicity scale from the abundance analysis of Nemec et al. (2013). We note, however, that the photometric metallicity of RR Lyr, the prototype and brightest star of the class, is significantly discrepant and poorly determined, as shown by the very large error bars. The reason likely is a poor determination of the *φ*<sub>31</sub> parameter for the star.

As already noted in Paper I, the photometric metallicities inferred from the [Fe/H], *P*, and *φ*<sub>31</sub> relation better represent the mean metal abundance of a population of RR Lyrae stars than the metallicity of the individual sources. Furthermore, new calibrations of this relation have appeared in the recent literature

<figure><img src="image_19.png" /><figcaption>**Fig. 19.** Error distribution of the metallicities derived for 133 557 DR3 RR Lyrae stars by the SOS pipeline. The mean and median metallicity errors are 0.46 dex (0.33 dex std) and 0.36 dex, respectively. We show only sources with $\sigma_{[Fe/H]} \le 2.0$ dex (i.e. 99.6% of the sample). We also note that for 71% of the sources in the plot, $\sigma_{[Fe/H]} \le 0.5$ dex.</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>**Fig. 20.** Comparison of the photometric metallicities derived by the SOS Cep&RRL pipeline and the metallicities from high-resolution spectra of 39 RR Lyrae stars of the Nemec et al. (2013) calibrators.</figcaption></figure>

(e.g. Iorio & Belokurov 2021; Mullen et al. 2021)<fnref n="6" />. Claims have been made by Iorio & Belokurov (2021) that metallicities based on the Nemec et al. (2013) calibrations are biased toward high metallicities. Conversely, Mullen et al. (2021) found an excellent agreement for higher metallicities in the Nemec et al. (2013) calibration range (−1.5 ≲ [Fe/H] ≲ 0.03 dex), while estimates diverge for lower metallicities.

In order to test the reliability of the RR Lyrae metallicities computed with the SOS pipeline, we compared them with the metal abundances from high-resolution spectroscopy available in the literature for different samples of RR Lyrae stars. Because the Mullen et al. (2021) relations are calibrated on the RR Lyrae metallicities from high-resolution spectra (R ~ 35 000) of Crestani et al. (2021), we discuss the comparison with Crestani et al. (2021) in the following. A comparison with other abundance analyses of RR Lyrae stars in the literature is presented in Appendix B.1.

First we compared the metal abundances from high-resolution spectra for RR Lyrae stars in common between Nemec et al. (2013) and Crestani et al. (2021). This comparison is shown in the left panel of Fig. 21 and seems to confirm that the Nemec et al. (2013) metallicities may be 0.1–0.2 dex higher than those of Crestani et al. (2021) for [Fe/H] ~ −1.5 dex.

<footnote n="6">⁶ We recall that the pipelines processing the Gaia data are frozen well in advance of releases. Specifically, the SOS Cep&RRL pipeline adopted to process the DR3 data was frozen in early 2020.</footnote>
<figure><img src="image_20.png" /><figcaption>**Fig. 21.** Left panel: comparison of the metallicity from high-resolution spectra for five RR Lyrae stars in common in Nemec et al. (2013) and Crestani et al. (2021). Right panel: comparison of the photometric metallicities derived by the SOS pipeline and the spectroscopic metallicities from high-resolution spectra derived by Crestani et al. (2021) for 105 RR Lyrae stars in common in the two samples. The two dashed lines are offset by ±0.46 dex, the mean error of the photometric metallicities (see Fig. 19), from the one-to-one line.</figcaption></figure>

<table><caption>**Table 1.** Metallicity and absorption in the G band for a sample of GCs and dSphs, obtained by averaging individual values derived by the SOS pipeline for the RR Lyrae stars in these systems.</caption><thead><tr><th>Name</th><th>[Fe/H]<sub>C09</sub><br>(dex)</th><th>RRLs<br>(N<sub>1</sub>)</th><th>[Fe/H]<sub>Gaia</sub><br>(dex)</th><th>St. dev. [Fe/H]<sub>Gaia</sub><br>(dex)</th><th>RRLs<br>(N<sub>2</sub>)</th><th>A(G)<br>(mag)</th><th>St. dev. [A(G)]<br>(mag)</th><th>A(G)<sup>(*)</sup><br>(mag)</th><th>Ref.</th></tr></thead><tbody><tr><td>NGC 1261</td><td>-1.27</td><td>14</td><td>-1.13</td><td>±0.49</td><td>12</td><td>1.32</td><td>±1.47</td><td>0.02</td><td>(1)</td></tr><tr><td>NGC 1851</td><td>-1.18</td><td>21</td><td>-1.11</td><td>±0.48</td><td>18</td><td>1.27</td><td>±1.06</td><td>0.05</td><td>(2)</td></tr><tr><td>NGC 288</td><td>-1.32</td><td>1</td><td>-1.24</td><td>±0.33</td><td>1</td><td>0.07</td><td>±0.08</td><td>0.08</td><td>(3)</td></tr><tr><td>NGC 3201</td><td>-1.59</td><td>73</td><td>-1.27</td><td>±0.36</td><td>77</td><td>0.73</td><td>±0.30</td><td>0.62</td><td>(4)</td></tr><tr><td>NGC 5024</td><td>-2.10</td><td>25</td><td>-1.66</td><td>±0.57</td><td>25</td><td>0.49</td><td>±0.69</td><td>0.05</td><td>(5)</td></tr><tr><td>NGC 5139-OCen</td><td>-1.53</td><td>36</td><td>-1.42</td><td>±0.63</td><td>39</td><td>0.43</td><td>±0.36</td><td>0.31</td><td>(6)</td></tr><tr><td>NGC 5272-M3</td><td>-1.50</td><td>125</td><td>-1.38</td><td>±0.39</td><td>105</td><td>0.89</td><td>±1.52</td><td>0.01</td><td>(7)</td></tr><tr><td>NGC 6266-M62</td><td>-1.18</td><td>105</td><td>-0.73</td><td>±0.36</td><td>88</td><td>2.77</td><td>±1.81</td><td>1.23</td><td>(8)</td></tr><tr><td>IC 4499</td><td>-1.53</td><td>64</td><td>-1.45</td><td>±0.48</td><td>58</td><td>0.66</td><td>±0.23</td><td>0.60</td><td>(9)</td></tr><tr><td>NGC 7078-M15</td><td>-2.37</td><td>44</td><td>-1.95</td><td>±0.54</td><td>30</td><td>0.89</td><td>±0.83</td><td>0.26</td><td>(10)</td></tr><tr><td>Sculptor</td><td>-1.68</td><td>289</td><td>-1.64</td><td>±0.50</td><td>275</td><td>0.53</td><td>±0.63</td><td>0.05</td><td>(11)</td></tr><tr><td>Draco</td><td>-1.93</td><td>258</td><td>-1.79</td><td>±0.67</td><td>216</td><td>0.54</td><td>±0.43</td><td>0.08</td><td>(12)</td></tr><tr><td>Ursa Major I</td><td>-2.18</td><td>5</td><td>-2.38</td><td>±0.43</td><td>5</td><td>1.94</td><td>±2.00</td><td>0.02</td><td>(13)</td></tr><tr><td>Ursa Major II</td><td>-2.47</td><td>1</td><td>-2.24</td><td>±0.45</td><td>3</td><td>0.26</td><td>±0.04</td><td>0.25</td><td>(14)</td></tr></tbody></table>

**Notes.** (*)A(G) values obtained by transforming the A(V) values in the literature using the following ratio of extinction coefficients A(G)/A(V) = 0.840 from Bono et al. (2019). N<sub>1</sub> and N<sub>2</sub> are the number of RR Lyrae stars on which the mean [Fe/H]<sub>Gaia</sub> and A(G) values were computed, with the corresponding standard deviation of the mean in Cols. 5 and 8, respectively.

**References.** (1) Salinas et al. (2016); (2) Walker (1998); (3) Kaluzny et al. (1997), Arellano Ferro et al. (2013); (4) Layden & Sarajedini (2003), Arellano Ferro et al. (2014); (5) Cuffey (1966), Goranskij (1976), Arellano Ferro et al. (2011); (6) Braga et al. (2018); (7) Benkő et al. (2006); (8) Contreras et al. (2010); (9) Walker & Nemec (1996); (10) Corwin et al. (2008); (11) Martínez-Vázquez et al. (2016); (12) Muraveva et al. (2020); (13) Garofalo et al. (2013); (14) Vivas et al. (2020).

The right panel of Fig. 21 shows the comparison of the photometric metallicities derived with the SOS Cep&RRL pipeline and the metal abundances from high-resolution spectra from Crestani et al. (2021) for 105 RR Lyrae stars in common in the two studies. As expected, this confirms the metallicity offset seen in the left panel of the figure, but the two sets of estimates are still generally consistent within the admittedly large errors of the SOS metallicities.

In Table 1 we compare available metallicities for a sample of globular clusters (GCs) and dwarf spheroidal galaxies (dSphs) with the metal abundances obtained by averaging individual photometric estimates from the SOS pipeline for RR Lyrae stars in these systems. The agreement is satisfactory, and except for M62, it is always within the standard deviations of the mean values estimated from the RR Lyrae stars.

Finally, the metallicity distributions of RR Lyrae stars in the all-sky, LMC, and SMC regions are shown with different colours in Fig. 22. A photometric metallicity estimate is avail-

able for 114 653 RR Lyrae in the all-sky region, for 16 295 in the LMC region, and for 2634 in the SMC region. The metallicity distributions peak at mean values of [Fe/H] = -1.07 ± 0.63, -1.31 ± 0.62, and -1.66 ± 0.66 dex for the all-sky, LMC, and SMC variables, respectively. The mean value estimated for the LMC variables is confirmed to be about 0.2 dex higher than reported by Gratton et al. (2004) from low-resolution (R ≈ 800) spectra of 98 RR Lyrae stars in the bar of the LMC: [Fe/H] = -1.48 ± 0.03 dex (on the Harris 1996 metallicity scale) and by Borissova et al. (2006), [Fe/H] = -1.53 ± 0.02 dex, from 78 RR Lyrae stars, covering a wide range of distances out to 2.5 degrees from the LMC centre.

## 5.2. Comparison with GSP_Spec metallicities

The astrophysical_parameters table in the Gaia DR3 archive contains metallicities derived with specific modules of the Apsis pipeline (Creevey et al. 2023) that analyse the Gaia
<figure><img src="image_21.png" /><figcaption>**Fig. 21.** Left panel: comparison of the metallicity from high-resolution spectra for five RR Lyrae stars in common in Nemec et al. (2013) and Crestani et al. (2021). Right panel: comparison of the photometric metallicities derived by the SOS pipeline and the spectroscopic metallicities from high-resolution spectra derived by Crestani et al. (2021) for 105 RR Lyrae stars in common in the two samples. The two dashed lines are offset by ±0.46 dex, the mean error of the photometric metallicities (see Fig. 19), from the one-to-one line.</figcaption></figure>

<table><caption>**Table 1.** Metallicity and absorption in the G band for a sample of GCs and dSphs, obtained by averaging individual values derived by the SOS pipeline for the RR Lyrae stars in these systems.</caption><thead><tr><th>Name</th><th>[Fe/H]<sub>C09</sub><br>(dex)</th><th>RRLs<br>(N<sub>1</sub>)</th><th>[Fe/H]<sub>Gaia</sub><br>(dex)</th><th>St. dev. [Fe/H]<sub>Gaia</sub><br>(dex)</th><th>RRLs<br>(N<sub>2</sub>)</th><th>A(G)<br>(mag)</th><th>St. dev. [A(G)]<br>(mag)</th><th>A(G)<sup>(*)</sup><br>(mag)</th><th>Ref.</th></tr></thead><tbody><tr><td>NGC 1261</td><td>-1.27</td><td>14</td><td>-1.13</td><td>±0.49</td><td>12</td><td>1.32</td><td>±1.47</td><td>0.02</td><td>(1)</td></tr><tr><td>NGC 1851</td><td>-1.18</td><td>21</td><td>-1.11</td><td>±0.48</td><td>18</td><td>1.27</td><td>±1.06</td><td>0.05</td><td>(2)</td></tr><tr><td>NGC 288</td><td>-1.32</td><td>1</td><td>-1.24</td><td>±0.33</td><td>1</td><td>0.07</td><td>±0.08</td><td>0.08</td><td>(3)</td></tr><tr><td>NGC 3201</td><td>-1.59</td><td>73</td><td>-1.27</td><td>±0.36</td><td>77</td><td>0.73</td><td>±0.30</td><td>0.62</td><td>(4)</td></tr><tr><td>NGC 5024</td><td>-2.10</td><td>25</td><td>-1.66</td><td>±0.57</td><td>25</td><td>0.49</td><td>±0.69</td><td>0.05</td><td>(5)</td></tr><tr><td>NGC 5139-OCen</td><td>-1.53</td><td>36</td><td>-1.42</td><td>±0.63</td><td>39</td><td>0.43</td><td>±0.36</td><td>0.31</td><td>(6)</td></tr><tr><td>NGC 5272-M3</td><td>-1.50</td><td>125</td><td>-1.38</td><td>±0.39</td><td>105</td><td>0.89</td><td>±1.52</td><td>0.01</td><td>(7)</td></tr><tr><td>NGC 6266-M62</td><td>-1.18</td><td>105</td><td>-0.73</td><td>±0.36</td><td>88</td><td>2.77</td><td>±1.81</td><td>1.23</td><td>(8)</td></tr><tr><td>IC 4499</td><td>-1.53</td><td>64</td><td>-1.45</td><td>±0.48</td><td>58</td><td>0.66</td><td>±0.23</td><td>0.60</td><td>(9)</td></tr><tr><td>NGC 7078-M15</td><td>-2.37</td><td>44</td><td>-1.95</td><td>±0.54</td><td>30</td><td>0.89</td><td>±0.83</td><td>0.26</td><td>(10)</td></tr><tr><td>Sculptor</td><td>-1.68</td><td>289</td><td>-1.64</td><td>±0.50</td><td>275</td><td>0.53</td><td>±0.63</td><td>0.05</td><td>(11)</td></tr><tr><td>Draco</td><td>-1.93</td><td>258</td><td>-1.79</td><td>±0.67</td><td>216</td><td>0.54</td><td>±0.43</td><td>0.08</td><td>(12)</td></tr><tr><td>Ursa Major I</td><td>-2.18</td><td>5</td><td>-2.38</td><td>±0.43</td><td>5</td><td>1.94</td><td>±2.00</td><td>0.02</td><td>(13)</td></tr><tr><td>Ursa Major II</td><td>-2.47</td><td>1</td><td>-2.24</td><td>±0.45</td><td>3</td><td>0.26</td><td>±0.04</td><td>0.25</td><td>(14)</td></tr></tbody></table>

**Notes.** (*)A(G) values obtained by transforming the A(V) values in the literature using the following ratio of extinction coefficients A(G)/A(V) = 0.840 from Bono et al. (2019). N<sub>1</sub> and N<sub>2</sub> are the number of RR Lyrae stars on which the mean [Fe/H]<sub>Gaia</sub> and A(G) values were computed, with the corresponding standard deviation of the mean in Cols. 5 and 8, respectively.

**References.** (1) Salinas et al. (2016); (2) Walker (1998); (3) Kaluzny et al. (1997), Arellano Ferro et al. (2013); (4) Layden & Sarajedini (2003), Arellano Ferro et al. (2014); (5) Cuffey (1966), Goranskij (1976), Arellano Ferro et al. (2011); (6) Braga et al. (2018); (7) Benkő et al. (2006); (8) Contreras et al. (2010); (9) Walker & Nemec (1996); (10) Corwin et al. (2008); (11) Martínez-Vázquez et al. (2016); (12) Muraveva et al. (2020); (13) Garofalo et al. (2013); (14) Vivas et al. (2020).

The right panel of Fig. 21 shows the comparison of the photometric metallicities derived with the SOS Cep&RRL pipeline and the metal abundances from high-resolution spectra from Crestani et al. (2021) for 105 RR Lyrae stars in common in the two studies. As expected, this confirms the metallicity offset seen in the left panel of the figure, but the two sets of estimates are still generally consistent within the admittedly large errors of the SOS metallicities.

In Table 1 we compare available metallicities for a sample of globular clusters (GCs) and dwarf spheroidal galaxies (dSphs) with the metal abundances obtained by averaging individual photometric estimates from the SOS pipeline for RR Lyrae stars in these systems. The agreement is satisfactory, and except for M62, it is always within the standard deviations of the mean values estimated from the RR Lyrae stars.

Finally, the metallicity distributions of RR Lyrae stars in the all-sky, LMC, and SMC regions are shown with different colours in Fig. 22. A photometric metallicity estimate is avail-

able for 114 653 RR Lyrae in the all-sky region, for 16 295 in the LMC region, and for 2634 in the SMC region. The metallicity distributions peak at mean values of [Fe/H] = -1.07 ± 0.63, -1.31 ± 0.62, and -1.66 ± 0.66 dex for the all-sky, LMC, and SMC variables, respectively. The mean value estimated for the LMC variables is confirmed to be about 0.2 dex higher than reported by Gratton et al. (2004) from low-resolution (R ≈ 800) spectra of 98 RR Lyrae stars in the bar of the LMC: [Fe/H] = -1.48 ± 0.03 dex (on the Harris 1996 metallicity scale) and by Borissova et al. (2006), [Fe/H] = -1.53 ± 0.02 dex, from 78 RR Lyrae stars, covering a wide range of distances out to 2.5 degrees from the LMC centre.

## 5.2. Comparison with GSP_Spec metallicities

The astrophysical_parameters table in the Gaia DR3 archive contains metallicities derived with specific modules of the Apsis pipeline (Creevey et al. 2023) that analyse the Gaia
<figure><img src="image_21.png" /><figcaption>**Fig. 23.** Left panel: comparison of the [M/H] metal abundances (mh_gspspec) computed with the GSP_Spec module of Apsis and [Fe/H] metallicities computed with the SOS Cep&RRL pipeline for 193 RR Lyrae stars for which both values are available. The two dashed lines are offset by ±0.46 dex, the mean error of the photometric metallicities (see Fig. 19), from the one-to-one line; right panel: same as in the left panel, but also showing the error bars of the [M/H]$_{GSP}$ and [Fe/H]$_{SOS}$ metallicities.</figcaption></figure>

likely an extreme case of temperature-extinction degeneracy due to GSP_Phot adopting incorrect mean temperatures for these RR Lyrae stars.

To conclude, as already pointed out for the GSP_Phot metal-
licities (Sect. 5.2), the comparison of the A(G) values shows
the difficulty of correctly inferring astrophysical parameters for
high-amplitude variables, such as the RR Lyrae stars, based on
time-averaged BP/RP spectra. We recommend that for RR Lyrae
stars (or for any other type of high amplitude pulsating variable
stars) the epoch BP/RP spectra are used individually (if their
S/N allows for it) along with epoch T<sub>eff</sub> and log g values, and
to then average the results to obtain more reliable GSP_Phot
metallicities and absorption values. On the other hand, as further
discussed in Appendix B, the SOS Cep&RRL and GSP_Phot
absorption values agree within ≈±0.2 mag for RR Lyrae stars
for which the GSP_Phot module uses T<sub>eff</sub> values in the proper
range for fundamental-mode RR Lyrae stars (e.g. 6300 < ∼ T<sub>eff</sub> < ∼
6800 K; see Col. 11 in Table A.3 and the top panel of Fig. B.5).
This is likely the case for about 14 000 RR Lyrae stars of the
84 501 sources for which both absorption estimates are avail-
able. We also find that for these same RR Lyrae strars, the SOS
Cep&RRL [Fe/H] values and the GSP_Phot metallicities agree
within ±0.5 dex.

**6. Final cleaning and validation of the DR3 RR Lyrae**
**catalogue**

During the final validation of the catalogue of 271 779
RR Lyrae stars that were confirmed and characterized with the
SOS pipeline, a number of issues, misclassifications, and uncer-
tain classifications were detected. In this section we discuss them
and provide tables with the identifiers of the affected sources. A
final statistics of the SOS confirmed DR3 RR Lyrae stars, cor-
rected for the issues described in this section, is presented in
Sect. 7.

**6.1. Mode identification for short-period RR Lyrae stars**

Short-period RRab stars with *P* ≲ 0.4 d overlap with RRc stars
in the *PA* diagram. In DR3 we have adopted new boundaries of
the RRab and RRc regions in the *PA* diagram to separate the
fundamental-mode from the first-overtone RR Lyrae stars (see
Sect. 2 and Fig. 3). However, some RRab stars were not captured
by the new boundaries and were incorrectly classified as RRc

<figure><img src="image_22.png" /><figcaption>**Fig. 24.** Error distribution in $\sigma_{A(G)}/A(G)$ of the $A(G)$ values computed with the StellarParametersDerivation module for 142 867 fundamental-mode RR Lyrae stars. Only sources for which $\sigma_{A(G)}$ is lower than 100% (81% of the RR Lyrae stars with an estimate of $A(G)$) are shown in the plot.</figcaption></figure>

stars. This is the case of the RRab stars 4297554691689496192 (*P* = 0.366 d) and 1826975050760883072 (*P* = 0.357 d). We caution that there may be a few more cases like these in the DR3 *vari Rae* table.

6.2. Double-mode RR Lyrae stars with Pf ≈ P1O

The parameters of 2007 double-mode RR Lyrae stars are pub-
lished in the DR3 vari Rae table. For 121 of them, the
two periodicities *Pf* and *P1O* that are listed in the table dif-
fer by less than 0.01 d. This was likely caused by a remapping
problem of *p1* and *p2*, the two periodicities detected in the time-
series photometry of these sources, into *Pf* (fundamental pul-
sation period) and *P1O* (first-overtone pulsation period). For all
these 121 sources, the *p1* and *p2* values differ and are in the
proper ratio for double-mode RR Lyrae stars. We provide the
correct *Pf* and *P1O* values computed by the SOS pipeline for
these 121 double-mode RR Lyrae stars in Table 2.

6.3. RR Lyrae stars with large or null errors for the main
parameters

The peak_to_peak bp, peak_to_peak rp, int_averag BP, and int_averag RP parameters of a number of RR Lyrae stars in the DR3 variUNE table have very large errors (see e.g. for source 4660156103061766400) or
<figure><img src="image_22.png" /><figcaption>**Fig. 23.** Left panel: comparison of the [M/H] metal abundances (mh_gspspec) computed with the GSP_Spec module of Apsis and [Fe/H] metallicities computed with the SOS Cep&RRL pipeline for 193 RR Lyrae stars for which both values are available. The two dashed lines are offset by ±0.46 dex, the mean error of the photometric metallicities (see Fig. 19), from the one-to-one line; right panel: same as in the left panel, but also showing the error bars of the [M/H]$_{GSP}$ and [Fe/H]$_{SOS}$ metallicities.</figcaption></figure>

likely an extreme case of temperature-extinction degeneracy due to GSP_Phot adopting incorrect mean temperatures for these RR Lyrae stars.

To conclude, as already pointed out for the GSP_Phot metal-
licities (Sect. 5.2), the comparison of the A(G) values shows
the difficulty of correctly inferring astrophysical parameters for
high-amplitude variables, such as the RR Lyrae stars, based on
time-averaged BP/RP spectra. We recommend that for RR Lyrae
stars (or for any other type of high amplitude pulsating variable
stars) the epoch BP/RP spectra are used individually (if their
S/N allows for it) along with epoch T<sub>eff</sub> and log g values, and
to then average the results to obtain more reliable GSP_Phot
metallicities and absorption values. On the other hand, as further
discussed in Appendix B, the SOS Cep&RRL and GSP_Phot
absorption values agree within ≈±0.2 mag for RR Lyrae stars
for which the GSP_Phot module uses T<sub>eff</sub> values in the proper
range for fundamental-mode RR Lyrae stars (e.g. 6300 < ∼ T<sub>eff</sub> < ∼
6800 K; see Col. 11 in Table A.3 and the top panel of Fig. B.5).
This is likely the case for about 14 000 RR Lyrae stars of the
84 501 sources for which both absorption estimates are avail-
able. We also find that for these same RR Lyrae strars, the SOS
Cep&RRL [Fe/H] values and the GSP_Phot metallicities agree
within ±0.5 dex.

**6. Final cleaning and validation of the DR3 RR Lyrae**
**catalogue**

During the final validation of the catalogue of 271 779
RR Lyrae stars that were confirmed and characterized with the
SOS pipeline, a number of issues, misclassifications, and uncer-
tain classifications were detected. In this section we discuss them
and provide tables with the identifiers of the affected sources. A
final statistics of the SOS confirmed DR3 RR Lyrae stars, cor-
rected for the issues described in this section, is presented in
Sect. 7.

**6.1. Mode identification for short-period RR Lyrae stars**

Short-period RRab stars with *P* ≲ 0.4 d overlap with RRc stars
in the *PA* diagram. In DR3 we have adopted new boundaries of
the RRab and RRc regions in the *PA* diagram to separate the
fundamental-mode from the first-overtone RR Lyrae stars (see
Sect. 2 and Fig. 3). However, some RRab stars were not captured
by the new boundaries and were incorrectly classified as RRc

<figure><img src="image_23.png" /><figcaption>**Fig. 24.** Error distribution in $\sigma_{A(G)}/A(G)$ of the $A(G)$ values computed with the StellarParametersDerivation module for 142 867 fundamental-mode RR Lyrae stars. Only sources for which $\sigma_{A(G)}$ is lower than 100% (81% of the RR Lyrae stars with an estimate of $A(G)$) are shown in the plot.</figcaption></figure>

stars. This is the case of the RRab stars 4297554691689496192 ($P$ = 0.366 d) and 1826975050760883072 ($P$ = 0.357 d). We caution that there may be a few more cases like these in the DR3 varibir table.

6.2. Double-mode RR Lyrae stars with Pf ≈ P1O

The parameters of 2007 double-mode RR Lyrae stars are pub-
lished in the DR3 varibir table. For 121 of them, the
two periodicities *Pf* and *P1O* that are listed in the table dif-
fer by less than 0.01 d. This was likely caused by a remapping
problem of *p1* and *p2*, the two periodicities detected in the time-
series photometry of these sources, into *Pf* (fundamental pul-
sation period) and *P1O* (first-overtone pulsation period). For all
these 121 sources, the *p1* and *p2* values differ and are in the
proper ratio for double-mode RR Lyrae stars. We provide the
correct *Pf* and *P1O* values computed by the SOS pipeline for
these 121 double-mode RR Lyrae stars in Table 2.

6.3. RR Lyrae stars with large or null errors for the main
parameters

The peak_to_peak bp, peak_to_peak rp, int_average bp, and int_average RP parameters of a number of RR Lyrae stars in the DR3 varibir table have very large errors (see e.g. for source 4660156103061766400) or
<figure><img src="image_23.png" /><figcaption>**Fig. 25.** Comparison of *G* absorption values derived by the GSP_Phot module of the Apsis pipeline (ag_gsppphot; Creevey et al. 2023) and the values derived by the SOS pipeline (g_absorption) for 84 501 RRab stars for which both estimates are available. The *A*(*G*) values are colour-coded according to the intensity-averaged *G* magnitudes of these RR Lyrae stars, as encoded in the colour scale on the right (see text for details).</figcaption></figure>

<table><caption>**Table 2.** Correct *Pf* and *P1O* periods for 121 double-mode RR Lyrae stars for which the two periodicites published in the *Gaia* DR3 *vari RRlyrae* table differ by less than 0.01 d.</caption><thead><tr><th><i>Gaia</i> sourceid</th><th><i>Pf</i></th><th><i>P1O</i></th></tr></thead><tbody><tr><td>408895729987233536</td><td>0.373330688241618</td><td>0.512642740772834</td></tr><tr><td>501173342860631808</td><td>0.356601096360751</td><td>0.479398897708066</td></tr><tr><td>510602690164934528</td><td>0.450007942826883</td><td>0.333771875260333</td></tr><tr><td>711991473282863616</td><td>0.405938896214094</td><td>0.544093988121247</td></tr><tr><td>799159586901582464</td><td>0.41546585867929</td><td>0.556716992103652</td></tr><tr><td>1009169258447656576</td><td>0.373435128605576</td><td>0.501424952889536</td></tr><tr><td>1019488037636107136</td><td>0.377019820562923</td><td>0.505549683973198</td></tr><tr><td>1300079698489198464</td><td>0.401148054398303</td><td>0.537722672814259</td></tr><tr><td>1323028808262955264</td><td>0.478288427372862</td><td>0.35013538941965</td></tr><tr><td>...</td><td>...</td><td>...</td></tr></tbody></table>

**Notes.** This table is available in its entirety at the CDS.

errors set to zero (see e.g. sources 4660223379454198144, 4685971467924582144, and 5027218748491264768). This happens for bona fide RR Lyrae stars with a mean *G* magnitude (*int_average_g*) fainter than 18.5–19 mag and sparse measurements with large errors in the *G*<sub>BP</sub> and *G*<sub>RP</sub> light curves. The affected sources are mainly in the Magellanic Clouds, in the Galactic bulge, and in a number of MW dSphs and UFDs.

Additionally, the *R*<sub>21</sub> (r21_g) and *R*<sub>31</sub> (r31_g) Fourier parameters of the *G* light curves for ~4400 DR3 RR Lyrae stars exceed the expected range of [0,1]. However, these limits are fully respected if the rather large errors associated with the *R*<sub>21</sub>, *R*<sub>31</sub> parameters of these sources are taken into account.

## 6.4. RR Lyrae stars with negative or very high *A*(*G*) values

The *G* absorption (*A*(*G*); *g_absorption* parameter) is negative (with values ranging from 0 to -1.279 mag) for 9503 DR3 RR Lyrae stars, corresponding to 6.3% of the 142 867 RR Lyrae stars with an *A*(*G*) value in the *vari RRlyrae* table (see Sect. 5.3), and it is higher than 10 mag (up to 3367.32 mag

<figure><img src="image_24.png" /><figcaption>**Fig. 26.** Sky distribution in galactic coordinates of 9 503 RR Lyrae stars with low/negative *A*(*G*) values (blue symbols) and 286 RR Lyrae stars with *A*(*G*) values higher than 10 magnitudes (red symbols).</figcaption></figure>

for source 5847675733921242624) for 286 sources (i.e. 0.2% of the RR Lyrae stars with an *A*(*G*) estimate).

As discussed in Sect. 5.3, 19% of the RR Lyrae stars with an *A*(*G*) estimate have |*σ*<sub>*A*(*G*)</sub>/*A*(*G*)| > 1. This is the case of all the 9503 sources with a negative *A*(*G*). Of these, 8033 have -0.1 < *A*(*G*) < 0 mag, 9 297 have -0.2 < *A*(*G*) < 0 mag, and 9487 have -0.5 < *A*(*G*) < 0 mag. The remaining sources (0.2%) with *A*(*G*) < -0.5 mag are fainter than *G* ~ 19 mag and therefore have uncertain (*G* - *G*<sub>RP</sub>) colours that affected the *A*(*G*) estimations.

Two hundred and eighty-six RRLyrae stars have high positive *A*(*G*) values, discarding the extreme case of 5847675733921242624, which clearly has an incorrect *A*(*G*) value. Of these, 77% have 0.007 < |*σ*<sub>*A*(*G*)</sub>/*A*(*G*)| < 0.2 and 91% have 0.007 < |*σ*<sub>*A*(*G*)</sub>/*A*(*G*)| < 0.5. The sky distribution of the RR Lyrae stars with low/negative or very high *A*(*G*) values is shown in Fig. 26 with blue symbols for the former and red symbols for the latter. As expected, the RR Lyrae stars with very high *A*(*G*) values are mainly confined in the Galactic disc and in regions with the highest reddening in the Magellanic Clouds, while RR Lyrae stars with a low/negative *A*(*G*) value are mainly located at high latitudes in the MW halo.
<figure><img src="image_24.png" /><figcaption>**Fig. 25.** Comparison of *G* absorption values derived by the GSP_Phot module of the Apsis pipeline (ag_gsppphot; Creevey et al. 2023) and the values derived by the SOS pipeline (g_absorption) for 84 501 RRab stars for which both estimates are available. The *A*(*G*) values are colour-coded according to the intensity-averaged *G* magnitudes of these RR Lyrae stars, as encoded in the colour scale on the right (see text for details).</figcaption></figure>

<table><caption>**Table 2.** Correct *Pf* and *P1O* periods for 121 double-mode RR Lyrae stars for which the two periodicites published in the *Gaia* DR3 *vari RRlyrae* table differ by less than 0.01 d.</caption><thead><tr><th><i>Gaia</i> sourceid</th><th><i>Pf</i></th><th><i>P1O</i></th></tr></thead><tbody><tr><td>408895729987233536</td><td>0.373330688241618</td><td>0.512642740772834</td></tr><tr><td>501173342860631808</td><td>0.356601096360751</td><td>0.479398897708066</td></tr><tr><td>510602690164934528</td><td>0.450007942826883</td><td>0.333771875260333</td></tr><tr><td>711991473282863616</td><td>0.405938896214094</td><td>0.544093988121247</td></tr><tr><td>799159586901582464</td><td>0.41546585867929</td><td>0.556716992103652</td></tr><tr><td>1009169258447656576</td><td>0.373435128605576</td><td>0.501424952889536</td></tr><tr><td>1019488037636107136</td><td>0.377019820562923</td><td>0.505549683973198</td></tr><tr><td>1300079698489198464</td><td>0.401148054398303</td><td>0.537722672814259</td></tr><tr><td>1323028808262955264</td><td>0.478288427372862</td><td>0.35013538941965</td></tr><tr><td>...</td><td>...</td><td>...</td></tr></tbody></table>

**Notes.** This table is available in its entirety at the CDS.

errors set to zero (see e.g. sources 4660223379454198144, 4685971467924582144, and 5027218748491264768). This happens for bona fide RR Lyrae stars with a mean *G* magnitude (*int_average_g*) fainter than 18.5–19 mag and sparse measurements with large errors in the *G*<sub>BP</sub> and *G*<sub>RP</sub> light curves. The affected sources are mainly in the Magellanic Clouds, in the Galactic bulge, and in a number of MW dSphs and UFDs.

Additionally, the *R*<sub>21</sub> (r21_g) and *R*<sub>31</sub> (r31_g) Fourier parameters of the *G* light curves for ~4400 DR3 RR Lyrae stars exceed the expected range of [0,1]. However, these limits are fully respected if the rather large errors associated with the *R*<sub>21</sub>, *R*<sub>31</sub> parameters of these sources are taken into account.

## 6.4. RR Lyrae stars with negative or very high A(G) values

The *G* absorption (*A*(*G*); *g_absorption* parameter) is negative (with values ranging from 0 to -1.279 mag) for 9503 DR3 RR Lyrae stars, corresponding to 6.3% of the 142 867 RR Lyrae stars with an *A*(*G*) value in the *vari RRlyrae* table (see Sect. 5.3), and it is higher than 10 mag (up to 3367.32 mag

<figure><img src="image_25.png" /><figcaption>**Fig. 26.** Sky distribution in galactic coordinates of 9 503 RR Lyrae stars with low/negative *A*(*G*) values (blue symbols) and 286 RR Lyrae stars with *A*(*G*) values higher than 10 magnitudes (red symbols).</figcaption></figure>

for source 5847675733921242624) for 286 sources (i.e. 0.2% of the RR Lyrae stars with an *A*(*G*) estimate).

As discussed in Sect. 5.3, 19% of the RR Lyrae stars with an *A*(*G*) estimate have |*σ*<sub>*A*(*G*)</sub>/*A*(*G*)| > 1. This is the case of all the 9503 sources with a negative *A*(*G*). Of these, 8033 have -0.1 < *A*(*G*) < 0 mag, 9 297 have -0.2 < *A*(*G*) < 0 mag, and 9487 have -0.5 < *A*(*G*) < 0 mag. The remaining sources (0.2%) with *A*(*G*) < -0.5 mag are fainter than *G* ~ 19 mag and therefore have uncertain (*G* - *G*<sub>RP</sub>) colours that affected the *A*(*G*) estimations.

Two hundred and eighty-six RRLyrae stars have high positive *A*(*G*) values, discarding the extreme case of 5847675733921242624, which clearly has an incorrect *A*(*G*) value. Of these, 77% have 0.007 < |*σ*<sub>*A*(*G*)</sub>/*A*(*G*)| < 0.2 and 91% have 0.007 < |*σ*<sub>*A*(*G*)</sub>/*A*(*G*)| < 0.5. The sky distribution of the RR Lyrae stars with low/negative or very high *A*(*G*) values is shown in Fig. 26 with blue symbols for the former and red symbols for the latter. As expected, the RR Lyrae stars with very high *A*(*G*) values are mainly confined in the Galactic disc and in regions with the highest reddening in the Magellanic Clouds, while RR Lyrae stars with a low/negative *A*(*G*) value are mainly located at high latitudes in the MW halo.
<table><caption>**Table 3.** 31 RR Lyrae stars in the Gaia DR3 *vari_rrlyrae* table that have a different classification in the OGLE catalogue.</caption><thead><tr><th>Gaia sourceid</th><th>⟨G⟩<br>(mag)</th><th>Revised type<br>(this paper)</th><th>Type<br>(OGLE-IV)</th></tr></thead><tbody><tr><td>4121189659364789632</td><td>18.407 ± 0.040</td><td>RRab</td><td>ACEP 1O</td></tr><tr><td>6724031478150071680</td><td>14.782 ± 0.007</td><td>RRab</td><td>ACEP 1O</td></tr><tr><td>3325594070648057344</td><td>13.304 ± 0.007</td><td>DCEP_1O</td><td>CEP 1O/2O</td></tr><tr><td>5259472605426820864</td><td>17.174 ± 0.002</td><td>DCEP_1O</td><td>CEP 1O/2O</td></tr><tr><td>5337626858335118080</td><td>17.471 ± 0.002</td><td>DCEP_1O</td><td>CEP 1O</td></tr><tr><td>5861856101075703552 (*)</td><td>13.398 ± 0.010</td><td>DCEP_MULTI</td><td>CEP F/1O</td></tr><tr><td>6025724977547669120</td><td>15.533 ± 0.010</td><td>DCEP_1O</td><td>CEP F/1O</td></tr><tr><td>4086063080350131968</td><td>13.863 ± 0.025</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>4088429190686315136</td><td>16.836 ± 0.021</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>4099638849167163648</td><td>13.514 ± 0.024</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>4123275364279164672</td><td>14.546 ± 0.004</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5253954057825909504</td><td>17.249 ± 0.005</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>5333097209687948032</td><td>19.000 ± 0.007</td><td>ACEP_F</td><td>ACEP 1O</td></tr><tr><td>5343906650256155392</td><td>15.834 ± 0.002</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5355902184686008832</td><td>14.863 ± 0.003</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5625331663591871104</td><td>17.862 ± 0.002</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5949793765379361152</td><td>17.784 ± 0.006</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5956690971798673664</td><td>15.261 ± 0.020</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>5970892843763951104</td><td>17.397 ± 0.003</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>5978313726930066048</td><td>16.533 ± 0.004</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5979051907235436160</td><td>17.042 ± 0.004</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>6026530163731660928</td><td>15.445 ± 0.009</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>6029981290235791232</td><td>15.607 ± 0.002</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>6724250895118108928</td><td>15.294 ± 0.003</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>4048728299707790976</td><td>15.562 ± 0.014</td><td>ACEP_1O/RRab?</td><td>ACEP 1O</td></tr><tr><td>4101192497784043520</td><td>14.931 ± 0.010</td><td>ACEP_1O/RRab?</td><td>ACEP 1O</td></tr><tr><td>4107356012051364480</td><td>15.654 ± 0.020</td><td>ACEP_1O/RRab?</td><td>ACEP 1O</td></tr><tr><td>5956833835251660800</td><td>15.975 ± 0.014</td><td>RRab/ACEP_F?</td><td>ACEP F</td></tr><tr><td>5968150764841574912</td><td>18.733 ± 0.005</td><td>ACEP_1O/RRab?</td><td>ACEP 1O</td></tr><tr><td>5980267829660152960</td><td>17.404 ± 0.005</td><td>ACEP_1O?/RRab?</td><td>ACEP 1O</td></tr><tr><td>6061867986376466688</td><td>16.290 ± 0.005</td><td>ACEP_F/RRab?</td><td>ACEP F</td></tr></tbody></table>

**Notes.** Based on a number of attributes, including their Gaia EDR3 parallax, the sources listed in the table are either confirmed as fundamental-mode RR Lyrae stars (2 sources), are reclassified as DCEPs (5 sources) or ACEPs (17 sources), or have an uncertain classification between RRab stars and ACEPs (7 sources). (*)This source is one of the 1100 RR Lyrae stars with RVS time-series RVs published in DR3.

## 6.5. RR Lyrae stars with a different classification in the OGLE catalogue

The Gaia DR3 *vari_rrlyrae* table lists 31 sources that the classifiers of the General Supervised Classification module in the variability analysis pipeline (Rimoldini et al. 2023) classified only as RR Lyrae candidates. They were therefore only processed through the RR Lyrae branch of the SOS Cep&RRL pipeline, which confirmed their classification as RR Lyrae stars. However, these sources are classified as Cepheids (5 as DCEPs and 26 as ACEPs) in the OGLE-IV catalogue of variable stars. Based on their Gaia EDR3 parallaxes, these sources were plotted on the period-luminosity (PL) and period-Wesenheit (PW) relations of DR3 Cepheids (see Table 2 in Ripepi et al. 2023). For two of them, the classification as RRab stars was confirmed, while 22 were reclassified as Cepheids (5 DCEPs and 17 ACEPs), and 7 have an uncertain classification between ACEPs or RRab stars. The sourceids of these 31 sources are provided in Table 3 along with their final classifications. One of the sources that was reclassified as DCEP (source 5861856101075703552) is included in the list of 1100 RR Lyrae stars with RVS time-series RVs published in DR3. Owing to this reclassification, the number of RR Lyrae stars with epoch RVs drops to

1099 and the Cepheid number increases to 799 (but see also Sect. 6.9).

## 6.6. RR Lyrae stars missing in the *vari_rrlyrae* table

The catalogue of 271779 RR Lyrae stars does not contain 14 bona fide RR Lyrae stars that were confirmed by the SOS Cep&RRL pipeline. They were mistakenly removed from the SOS final catalogue, but are listed in the *varirisolver* table. Table 4 gives the sourceids of these 14 RR Lyrae stars, and in Table C.1 we provide the parameters (*P*, peak-to-peak *G*, *G*<sub>BP</sub>, *G*<sub>RP</sub> amplitudes, mean magnitudes, etc.) that were computed by the SOS pipeline for these sources.

## 6.7. Overlaps with pipelines that process galaxies and QSOs

A total of 1139 sources in the *vari_rrlyrae* table are classified as galaxies by other DPAC pipelines. After visual inspection of their light curves, 618 of them were confirmed as RR Lyrae stars, more than 400 of which are known RR Lyrae stars in the OGLE-IV catalogue or in the catalogue of variable stars
<table><caption>**Table 3.** 31 RR Lyrae stars in the Gaia DR3 *vari_rrlyrae* table that have a different classification in the OGLE catalogue.</caption><thead><tr><th>Gaia sourceid</th><th>⟨G⟩<br>(mag)</th><th>Revised type<br>(this paper)</th><th>Type<br>(OGLE-IV)</th></tr></thead><tbody><tr><td>4121189659364789632</td><td>18.407 ± 0.040</td><td>RRab</td><td>ACEP 1O</td></tr><tr><td>6724031478150071680</td><td>14.782 ± 0.007</td><td>RRab</td><td>ACEP 1O</td></tr><tr><td>3325594070648057344</td><td>13.304 ± 0.007</td><td>DCEP_1O</td><td>CEP 1O/2O</td></tr><tr><td>5259472605426820864</td><td>17.174 ± 0.002</td><td>DCEP_1O</td><td>CEP 1O/2O</td></tr><tr><td>5337626858335118080</td><td>17.471 ± 0.002</td><td>DCEP_1O</td><td>CEP 1O</td></tr><tr><td>5861856101075703552 (*)</td><td>13.398 ± 0.010</td><td>DCEP_MULTI</td><td>CEP F/1O</td></tr><tr><td>6025724977547669120</td><td>15.533 ± 0.010</td><td>DCEP_1O</td><td>CEP F/1O</td></tr><tr><td>4086063080350131968</td><td>13.863 ± 0.025</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>4088429190686315136</td><td>16.836 ± 0.021</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>4099638849167163648</td><td>13.514 ± 0.024</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>4123275364279164672</td><td>14.546 ± 0.004</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5253954057825909504</td><td>17.249 ± 0.005</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>5333097209687948032</td><td>19.000 ± 0.007</td><td>ACEP_F</td><td>ACEP 1O</td></tr><tr><td>5343906650256155392</td><td>15.834 ± 0.002</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5355902184686008832</td><td>14.863 ± 0.003</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5625331663591871104</td><td>17.862 ± 0.002</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5949793765379361152</td><td>17.784 ± 0.006</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5956690971798673664</td><td>15.261 ± 0.020</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>5970892843763951104</td><td>17.397 ± 0.003</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>5978313726930066048</td><td>16.533 ± 0.004</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>5979051907235436160</td><td>17.042 ± 0.004</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>6026530163731660928</td><td>15.445 ± 0.009</td><td>ACEP_F</td><td>ACEP F</td></tr><tr><td>6029981290235791232</td><td>15.607 ± 0.002</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>6724250895118108928</td><td>15.294 ± 0.003</td><td>ACEP_1O</td><td>ACEP 1O</td></tr><tr><td>4048728299707790976</td><td>15.562 ± 0.014</td><td>ACEP_1O/RRab?</td><td>ACEP 1O</td></tr><tr><td>4101192497784043520</td><td>14.931 ± 0.010</td><td>ACEP_1O/RRab?</td><td>ACEP 1O</td></tr><tr><td>4107356012051364480</td><td>15.654 ± 0.020</td><td>ACEP_1O/RRab?</td><td>ACEP 1O</td></tr><tr><td>5956833835251660800</td><td>15.975 ± 0.014</td><td>RRab/ACEP_F?</td><td>ACEP F</td></tr><tr><td>5968150764841574912</td><td>18.733 ± 0.005</td><td>ACEP_1O/RRab?</td><td>ACEP 1O</td></tr><tr><td>5980267829660152960</td><td>17.404 ± 0.005</td><td>ACEP_1O?/RRab?</td><td>ACEP 1O</td></tr><tr><td>6061867986376466688</td><td>16.290 ± 0.005</td><td>ACEP_F/RRab?</td><td>ACEP F</td></tr></tbody></table>

**Notes.** Based on a number of attributes, including their Gaia EDR3 parallax, the sources listed in the table are either confirmed as fundamental-mode RR Lyrae stars (2 sources), are reclassified as DCEPs (5 sources) or ACEPs (17 sources), or have an uncertain classification between RRab stars and ACEPs (7 sources). (*)This source is one of the 1100 RR Lyrae stars with RVS time-series RVs published in DR3.

## 6.5. RR Lyrae stars with a different classification in the OGLE catalogue

The Gaia DR3 *vari_rrlyrae* table lists 31 sources that the classifiers of the General Supervised Classification module in the variability analysis pipeline (Rimoldini et al. 2023) classified only as RR Lyrae candidates. They were therefore only processed through the RR Lyrae branch of the SOS Cep&RRL pipeline, which confirmed their classification as RR Lyrae stars. However, these sources are classified as Cepheids (5 as DCEPs and 26 as ACEPs) in the OGLE-IV catalogue of variable stars. Based on their Gaia EDR3 parallaxes, these sources were plotted on the period-luminosity (PL) and period-Wesenheit (PW) relations of DR3 Cepheids (see Table 2 in Ripepi et al. 2023). For two of them, the classification as RRab stars was confirmed, while 22 were reclassified as Cepheids (5 DCEPs and 17 ACEPs), and 7 have an uncertain classification between ACEPs or RRab stars. The sourceids of these 31 sources are provided in Table 3 along with their final classifications. One of the sources that was reclassified as DCEP (source 5861856101075703552) is included in the list of 1100 RR Lyrae stars with RVS time-series RVs published in DR3. Owing to this reclassification, the number of RR Lyrae stars with epoch RVs drops to

1099 and the Cepheid number increases to 799 (but see also Sect. 6.9).

## 6.6. RR Lyrae stars missing in the *vari_rrlyrae* table

The catalogue of 271779 RR Lyrae stars does not contain 14 bona fide RR Lyrae stars that were confirmed by the SOS Cep&RRL pipeline. They were mistakenly removed from the SOS final catalogue, but are listed in the *varirisolver* table. Table 4 gives the sourceids of these 14 RR Lyrae stars, and in Table C.1 we provide the parameters (*P*, peak-to-peak *G*, *G*<sub>BP</sub>, *G*<sub>RP</sub> amplitudes, mean magnitudes, etc.) that were computed by the SOS pipeline for these sources.

## 6.7. Overlaps with pipelines that process galaxies and QSOs

A total of 1139 sources in the *vari_rrlyrae* table are classified as galaxies by other DPAC pipelines. After visual inspection of their light curves, 618 of them were confirmed as RR Lyrae stars, more than 400 of which are known RR Lyrae stars in the OGLE-IV catalogue or in the catalogue of variable stars
<table><caption>**Table 4.** 14 bona fide RR Lyrae stars that were mistakenly removed from the SOS RR Lyrae catalogue.</caption><thead><tr><th>Gaia DR3 sourceid</th></tr></thead><tbody><tr><td>4092009204924599040</td></tr><tr><td>4120414435009794048</td></tr><tr><td>4144246349481643392</td></tr><tr><td>5797652730842515968</td></tr><tr><td>5797917193442176640</td></tr><tr><td>5846086424210395520</td></tr><tr><td>5917239841741208576</td></tr><tr><td>5991733644318583424</td></tr><tr><td>6017924835910361344</td></tr><tr><td>6069336998880602240</td></tr><tr><td>6707009423228603904</td></tr><tr><td>5935214760885709440</td></tr><tr><td>4362766825101261952</td></tr><tr><td>5967334102579505664</td></tr></tbody></table>

**Notes.** The sources in this table do not appear in the *vari RRlyrae* table, but are listed in the *vari classifier result* table. The SOS Cep&RRL parameters for these 14 RR Lyrae stars are provided in Table C.1.

<table><caption>**Table 5.** 521 sources in the *Gaia* DR3 *vari rrlyrae* table that are classified as galaxies or non-single/extended objects by other DPAC pipelines.</caption><thead><tr><th>Gaia DR3 source id</th><th>Tentative class <sup>(*)</sup></th></tr></thead><tbody><tr><td>252947980027906048</td><td>RR Lyrae?</td></tr><tr><td>367375357718907776</td><td>galaxy/QSO</td></tr><tr><td>392996452549916416</td><td>...</td></tr><tr><td>406587893736299136</td><td>...</td></tr><tr><td>419307353484601472</td><td>...</td></tr><tr><td>3206068021312873728</td><td>...</td></tr><tr><td>1056196096618040960</td><td>...</td></tr><tr><td>5571533079335954816</td><td>...</td></tr><tr><td>4685908211622296576</td><td>...</td></tr><tr><td>4928220400858440704</td><td>...</td></tr><tr><td>...</td><td>...</td></tr></tbody></table>

**Notes.** The entries in this table either are clearly not RR Lyrae stars or are sources for which the SOS Cep&RRL pipeline classification as RR Lyrae stars is uncertain (see Col. 2). (*)Tentative classification after visual inspection of the light curves. The table is available in its entirety at the CDS.

in GCs. The remaining 521 sources are listed in Table 5. The majority of them are rather faint sources ($G > 20$ mag) and are either clearly not RR Lyrae stars or have an uncertain classification.

About 57 000 RR Lyrae stars in the *vari rrlyrae* table are classified as QSOs by other DPAC pipelines. Of these, 55 448 are known RR Lyrae stars (~30 000 from the OGLE-IV catalogue and ~25 400 from other main catalogues of RR Lyrae stars in the literature). We visually inspected the light curves of the remaining 1635 sources and confirmed the classification as RR Lyrae stars for 1353 of them (80 of them are classified as RR Lyrae stars in the SIMBAD database as well; Wenger et al. 2000). The remaining 282 sources that are listed in Table 6 are either clearly not RR Lyrae stars or have an uncertain classification.

<table><caption>**Table 6.** 282 sources in the *Gaia* DR3 *vari rrlyrae* table that are classified as QSOs by other DPAC pipelines.</caption><thead><tr><th>Gaia DR3 sourceid</th><th>Class <sup>(*)</sup></th></tr></thead><tbody><tr><td>5710645592594769280</td><td>ECL</td></tr><tr><td>5246357493290558336</td><td>ECL</td></tr><tr><td>4661507982702013312</td><td>...</td></tr><tr><td>5116113679481496832</td><td>...</td></tr><tr><td>2456881998103809280</td><td>...</td></tr><tr><td>1305269977485608192</td><td>...</td></tr><tr><td>6242394047412731520</td><td>...</td></tr><tr><td>...</td><td>...</td></tr></tbody></table>

**Notes.** The entries in this table either are clearly not RR Lyrae stars or are sources with an uncertain classification. (*)Classification after visual inspection of the light curves. This table is available in its entirety at the CDS.

<table><caption>**Table 7.** Eighty bona fide RRab stars in the *Gaia* DR3 *vari rrlyrae* table that are identified as non-single star by the SEAPipe pipeline.</caption><thead><tr><th>Gaia DR3 source id</th></tr></thead><tbody><tr><td>4061010604884154624</td></tr><tr><td>4097861458597689856</td></tr><tr><td>4043627562186192768</td></tr><tr><td>1827951859436521728</td></tr><tr><td>6045465845526924544</td></tr><tr><td>...</td></tr></tbody></table>

**Notes.** This table is available in its entirety at the CDS.

## 6.8. Non-single star sources identified with SEAPipe

The DPAC-Source Environment Analysis Pipeline (SEAPipe; Harrison 2011; Harrison et al., in prep.) was run on the catalogue of 271 779 RR Lyrae stars confirmed by the SOS Cep&RRL pipeline to determine whether additional sources are present in the vicinity (within a radius of ~2") that might contaminate the light of the RR Lyrae stars. SEAPipe returned a list of 80 RR Lyrae stars that were found to be non-single sources. These 80 sources mainly lie in the MW bulge and disc, 79 of them are RR Lyrae stars already known in the literature (67 are in the OGLE-IV catalogue and 12 in the ZTF and Gaia DR2 catalogues), only one is a new discovery. Visual inspection of the light curves allowed us to confirm that they are all *ab*-type RR Lyrae stars, with different levels of noise particularly in the $G_{BP}$ and $G_{RP}$ light curves that is often also accompanied by a reduced amplitude of the *G*-band light curve. These are clear signatures of contamination and blending by neighboring stars (see e.g. Fig 16 in Di Fabrizio et al. 2005) that can affect the estimated mean magnitude and peak-to-peak amplitudes of these RR Lyrae stars, but not the derived periods. We list these 80 RRab stars in Table 7 and caution about the use of amplitudes, mean magnitudes, Fourier parameters, and derived quantities of these sources.

## 6.9. Contamination by binaries and other types of variable stars

RR Lyrae stars in the *vari rrlyrae* with *Gaia* DR3 parallaxes accurate to better than 5% were plotted on a PW($G, G_{BP}$ - $G_{RP}$) relation along with DR3 Cepheids with same parallax accuracy (see Ripepi et al. 2023, for details). A group of 147
<table><caption>**Table 4.** 14 bona fide RR Lyrae stars that were mistakenly removed from the SOS RR Lyrae catalogue.</caption><thead><tr><th>Gaia DR3 sourceid</th></tr></thead><tbody><tr><td>4092009204924599040</td></tr><tr><td>4120414435009794048</td></tr><tr><td>4144246349481643392</td></tr><tr><td>5797652730842515968</td></tr><tr><td>5797917193442176640</td></tr><tr><td>5846086424210395520</td></tr><tr><td>5917239841741208576</td></tr><tr><td>5991733644318583424</td></tr><tr><td>6017924835910361344</td></tr><tr><td>6069336998880602240</td></tr><tr><td>6707009423228603904</td></tr><tr><td>5935214760885709440</td></tr><tr><td>4362766825101261952</td></tr><tr><td>5967334102579505664</td></tr></tbody></table>

**Notes.** The sources in this table do not appear in the *vari RRlyrae* table, but are listed in the *vari classifier result* table. The SOS Cep&RRL parameters for these 14 RR Lyrae stars are provided in Table C.1.

<table><caption>**Table 5.** 521 sources in the *Gaia* DR3 *vari rrlyrae* table that are classified as galaxies or non-single/extended objects by other DPAC pipelines.</caption><thead><tr><th>Gaia DR3 source id</th><th>Tentative class <sup>(*)</sup></th></tr></thead><tbody><tr><td>252947980027906048</td><td>RR Lyrae?</td></tr><tr><td>367375357718907776</td><td>galaxy/QSO</td></tr><tr><td>392996452549916416</td><td>...</td></tr><tr><td>406587893736299136</td><td>...</td></tr><tr><td>419307353484601472</td><td>...</td></tr><tr><td>3206068021312873728</td><td>...</td></tr><tr><td>1056196096618040960</td><td>...</td></tr><tr><td>5571533079335954816</td><td>...</td></tr><tr><td>4685908211622296576</td><td>...</td></tr><tr><td>4928220400858440704</td><td>...</td></tr><tr><td>...</td><td>...</td></tr></tbody></table>

**Notes.** The entries in this table either are clearly not RR Lyrae stars or are sources for which the SOS Cep&RRL pipeline classification as RR Lyrae stars is uncertain (see Col. 2). (*)Tentative classification after visual inspection of the light curves. The table is available in its entirety at the CDS.

in GCs. The remaining 521 sources are listed in Table 5. The majority of them are rather faint sources ($G > 20$ mag) and are either clearly not RR Lyrae stars or have an uncertain classification.

About 57 000 RR Lyrae stars in the *vari rrlyrae* table are classified as QSOs by other DPAC pipelines. Of these, 55 448 are known RR Lyrae stars (~30 000 from the OGLE-IV catalogue and ~25 400 from other main catalogues of RR Lyrae stars in the literature). We visually inspected the light curves of the remaining 1635 sources and confirmed the classification as RR Lyrae stars for 1353 of them (80 of them are classified as RR Lyrae stars in the SIMBAD database as well; Wenger et al. 2000). The remaining 282 sources that are listed in Table 6 are either clearly not RR Lyrae stars or have an uncertain classification.

<table><caption>**Table 6.** 282 sources in the *Gaia* DR3 *vari rrlyrae* table that are classified as QSOs by other DPAC pipelines.</caption><thead><tr><th>Gaia DR3 sourceid</th><th>Class <sup>(*)</sup></th></tr></thead><tbody><tr><td>5710645592594769280</td><td>ECL</td></tr><tr><td>5246357493290558336</td><td>ECL</td></tr><tr><td>4661507982702013312</td><td>...</td></tr><tr><td>5116113679481496832</td><td>...</td></tr><tr><td>2456881998103809280</td><td>...</td></tr><tr><td>1305269977485608192</td><td>...</td></tr><tr><td>6242394047412731520</td><td>...</td></tr><tr><td>...</td><td>...</td></tr></tbody></table>

**Notes.** The entries in this table either are clearly not RR Lyrae stars or are sources with an uncertain classification. (*)Classification after visual inspection of the light curves. This table is available in its entirety at the CDS.

<table><caption>**Table 7.** Eighty bona fide RRab stars in the *Gaia* DR3 *vari rrlyrae* table that are identified as non-single star by the SEAPipe pipeline.</caption><thead><tr><th>Gaia DR3 source id</th></tr></thead><tbody><tr><td>4061010604884154624</td></tr><tr><td>4097861458597689856</td></tr><tr><td>4043627562186192768</td></tr><tr><td>1827951859436521728</td></tr><tr><td>6045465845526924544</td></tr><tr><td>...</td></tr></tbody></table>

**Notes.** This table is available in its entirety at the CDS.

## 6.8. Non-single star sources identified with SEAPipe

The DPAC-Source Environment Analysis Pipeline (SEAPipe; Harrison 2011; Harrison et al., in prep.) was run on the catalogue of 271 779 RR Lyrae stars confirmed by the SOS Cep&RRL pipeline to determine whether additional sources are present in the vicinity (within a radius of ~2") that might contaminate the light of the RR Lyrae stars. SEAPipe returned a list of 80 RR Lyrae stars that were found to be non-single sources. These 80 sources mainly lie in the MW bulge and disc, 79 of them are RR Lyrae stars already known in the literature (67 are in the OGLE-IV catalogue and 12 in the ZTF and Gaia DR2 catalogues), only one is a new discovery. Visual inspection of the light curves allowed us to confirm that they are all *ab*-type RR Lyrae stars, with different levels of noise particularly in the $G_{BP}$ and $G_{RP}$ light curves that is often also accompanied by a reduced amplitude of the *G*-band light curve. These are clear signatures of contamination and blending by neighboring stars (see e.g. Fig 16 in Di Fabrizio et al. 2005) that can affect the estimated mean magnitude and peak-to-peak amplitudes of these RR Lyrae stars, but not the derived periods. We list these 80 RRab stars in Table 7 and caution about the use of amplitudes, mean magnitudes, Fourier parameters, and derived quantities of these sources.

## 6.9. Contamination by binaries and other types of variable stars

RR Lyrae stars in the *vari rrlyrae* with *Gaia* DR3 parallaxes accurate to better than 5% were plotted on a PW($G, G_{BP}$ - $G_{RP}$) relation along with DR3 Cepheids with same parallax accuracy (see Ripepi et al. 2023, for details). A group of 147
<figure><img src="image_25.png" /><figcaption>**Fig. 27.** Distribution in *G* magnitude of the clean sample of 270 905 DR3 RR Lyrae stars confirmed with the SOS Cep&RRL pipeline. The peaks at *G* ~ 19.2, 19.7 mag correspond to RR Lyrae stars in the LMC and SMC, respectively. The magnitude distribution of the 70 611 new RR Lyrae stars is highlighted in black.</figcaption></figure>

<table><caption>**Table 10.** Statistics of the RR Lyrae stars confirmed by the SOS Cep&RRL pipeline that are published in DR3.</caption><thead><tr><th>Sample</th><th>N(-14)<br>vari_-rrlyrae</th><th>N<sub>clean</sub>(-14)</th><th>N<sub>clean</sub>(+14)</th></tr></thead><tbody><tr><td>Gold Sample</td><td>200 589</td><td>200 293</td><td>200 294</td></tr><tr><td>New discoveries <sup>(a)</sup></td><td>71 190</td><td>70 598</td><td>70 611</td></tr><tr><td>Total number of RR Lyrae stars</td><td>271 779</td><td>270 891</td><td>270 905</td></tr><tr><td>LMC region <sup>(b)</sup></td><td>31 535</td><td>31 379</td><td>31 379</td></tr><tr><td>SMC region <sup>(b)</sup></td><td>4828</td><td>4788</td><td>4788</td></tr><tr><td>All-Sky region <sup>(b)</sup></td><td>235 416</td><td>234 724</td><td>234 738</td></tr><tr><td>Fundamental mode (RRab) <sup>(c)</sup></td><td>175 350</td><td>174 943</td><td>174 947</td></tr><tr><td>First overtone (RRc) <sup>(c)</sup></td><td>94 422</td><td>93 942</td><td>93 952</td></tr><tr><td>Double mode (RRd)</td><td>2007</td><td>2006</td><td>2006</td></tr><tr><td>[Fe/H] values (RRab and RRc)</td><td>133 577</td><td>133 558</td><td>133 559</td></tr><tr><td>A(G) values (RRab only)</td><td>142 867</td><td>142 656</td><td>142 660</td></tr><tr><td>RV time series (RR Lyrae) <sup>(d)</sup></td><td>1100</td><td>1096</td><td>1096</td></tr><tr><td>RV time series (Cepheids) <sup>(d)</sup></td><td>798</td><td>799</td><td>799</td></tr><tr><td>RV time series (other type)</td><td>...</td><td>3</td><td>3</td></tr><tr><td>Total number of sources with RV time series data</td><td>1898</td><td>1898</td><td>1898</td></tr></tbody></table>

**Notes.** Numbers in Cols. 2 and 3 correspond to the samples before and after the validation and cleaning described in Sect. 6, respectively. Numbers in Col. 4 are after adding the 14 RR Lyrae stars discussed in Sect. 6.6. <sup>(a)</sup>“New” means “new to the best of our knowledge”. <sup>(b)</sup>Regions for the LMC, SMC, and all-sky are as defined in Sect. 2. <sup>(c)</sup>Numbers of RRab and RRc stars in column $N_{clean}(-14)$ are corrected for the reclassifications in Sect. 6.1. <sup>(d)</sup>Numbers of RR Lyrae and Cepheids with RV time-series data published in DR3 are corrected in column $N_{clean}(-14)$ for the reclassifications in Sects. 6.5 and 6.9.

- RR Lyrae subclassification into RRab, RRc, and RRd types;

- absorption in the *G* band, $A(G)$, for RRab stars; and

- photometric metallicity, [Fe/H], for RRab and RRc stars.

The SOS Cep&RRL parameters for the 14 bona fide RR Lyrae stars that do not appear in the *vari_-rrlyrae* table (see Sect. 6.6) are instead provided in Table C.1.

*Gaia* sourceids, coordinates, *G*, *G*<sub>BP</sub>, and *G*<sub>RP</sub> time-series photometry for each of the 270 905 RR Lyrae stars (and for the 888 rejected sources) and RVS time-series RVs for 1895 sources between RR Lyrae stars and Cepheids and for three RR Lyrae stars that were reclassified as ECLs can be retrieved from the

*Gaia* data release archive<sup>8</sup> and its mirror nodes. The archives also provide tools for queries and a cross-match of *Gaia* data with other catalogues in the literature.

We provide in Table 12 the specific link to the *vari_-rrlyrae* table of the *Gaia* DR3 archive and summarise the names of the parameters computed with SOS Cep&RRL that can be retrieved for RR Lyrae stars from the archive table. Finally, in Appendix E, we give examples of queries to retrieve some of the quantities and parameters listed in Table 12.

<footnote n="8">8 http://archives.esac.esa.int/gaia/</footnote>
<figure><img src="image_26.png" /><figcaption>**Fig. 27.** Distribution in *G* magnitude of the clean sample of 270 905 DR3 RR Lyrae stars confirmed with the SOS Cep&RRL pipeline. The peaks at *G* ~ 19.2, 19.7 mag correspond to RR Lyrae stars in the LMC and SMC, respectively. The magnitude distribution of the 70 611 new RR Lyrae stars is highlighted in black.</figcaption></figure>

<table><caption>**Table 10.** Statistics of the RR Lyrae stars confirmed by the SOS Cep&RRL pipeline that are published in DR3.</caption><thead><tr><th>Sample</th><th>N(-14)<br>vari_rrlyrae</th><th>N<sub>clean</sub>(-14)</th><th>N<sub>clean</sub>(+14)</th></tr></thead><tbody><tr><td>Gold Sample</td><td>200 589</td><td>200 293</td><td>200 294</td></tr><tr><td>New discoveries <sup>(a)</sup></td><td>71 190</td><td>70 598</td><td>70 611</td></tr><tr><td>Total number of RR Lyrae stars</td><td>271 779</td><td>270 891</td><td>270 905</td></tr><tr><td>LMC region <sup>(b)</sup></td><td>31 535</td><td>31 379</td><td>31 379</td></tr><tr><td>SMC region <sup>(b)</sup></td><td>4828</td><td>4788</td><td>4788</td></tr><tr><td>All-Sky region <sup>(b)</sup></td><td>235 416</td><td>234 724</td><td>234 738</td></tr><tr><td>Fundamental mode (RRab) <sup>(c)</sup></td><td>175 350</td><td>174 943</td><td>174 947</td></tr><tr><td>First overtone (RRc) <sup>(c)</sup></td><td>94 422</td><td>93 942</td><td>93 952</td></tr><tr><td>Double mode (RRd)</td><td>2007</td><td>2006</td><td>2006</td></tr><tr><td>[Fe/H] values (RRab and RRc)</td><td>133 577</td><td>133 558</td><td>133 559</td></tr><tr><td>A(G) values (RRab only)</td><td>142 867</td><td>142 656</td><td>142 660</td></tr><tr><td>RV time series (RR Lyrae) <sup>(d)</sup></td><td>1100</td><td>1096</td><td>1096</td></tr><tr><td>RV time series (Cepheids) <sup>(d)</sup></td><td>798</td><td>799</td><td>799</td></tr><tr><td>RV time series (other type)</td><td>...</td><td>3</td><td>3</td></tr><tr><td>Total number of sources with RV time series data</td><td>1898</td><td>1898</td><td>1898</td></tr></tbody></table>

**Notes.** Numbers in Cols. 2 and 3 correspond to the samples before and after the validation and cleaning described in Sect. 6, respectively. Numbers in Col. 4 are after adding the 14 RR Lyrae stars discussed in Sect. 6.6. <sup>(a)</sup>“New” means “new to the best of our knowledge”. <sup>(b)</sup>Regions for the LMC, SMC, and all-sky are as defined in Sect. 2. <sup>(c)</sup>Numbers of RRab and RRc stars in column $N_{clean}(-14)$ are corrected for the reclassifications in Sect. 6.1. <sup>(d)</sup>Numbers of RR Lyrae and Cepheids with RV time-series data published in DR3 are corrected in column $N_{clean}(-14)$ for the reclassifications in Sects. 6.5 and 6.9.

- RR Lyrae subclassification into RRab, RRc, and RRd types;

- absorption in the *G* band, $A(G)$, for RRab stars; and

- photometric metallicity, [Fe/H], for RRab and RRc stars.

The SOS Cep&RRL parameters for the 14 bona fide RR Lyrae stars that do not appear in the *vari_rrlyrae* table (see Sect. 6.6) are instead provided in Table C.1.

Gaia sourceids, coordinates, *G*, *G*<sub>BP</sub>, and *G*<sub>RP</sub> time-series photometry for each of the 270 905 RR Lyrae stars (and for the 888 rejected sources) and RVS time-series RVs for 1895 sources between RR Lyrae stars and Cepheids and for three RR Lyrae stars that were reclassified as ECLs can be retrieved from the

Gaia data release archive<fnref n="8" /> and its mirror nodes. The archives also provide tools for queries and a cross-match of Gaia data with other catalogues in the literature.

We provide in Table 12 the specific link to the *vari_rrlyrae* table of the Gaia DR3 archive and summarise the names of the parameters computed with SOS Cep&RRL that can be retrieved for RR Lyrae stars from the archive table. Finally, in Appendix E, we give examples of queries to retrieve some of the quantities and parameters listed in Table 12.

<footnote n="8">⁸ http://archives.esac.esa.int/gaia/</footnote>
<table><caption>**Table 12.** Links to the Gaia archive table to retrieve pulsation characteristics, metallicity, and absorption in the G band computed by the SOS Cep&RRL pipeline for 270 891 confirmed RR Lyrae stars (and for 888 rejected sources listed in Table 9) that are released in Gaia DR3.</caption><thead><tr><th>Table URL</th><th>https://gea.esac.esa.int/archive/</th></tr></thead><tbody><tr><td colspan="2">RR Lyrae main parameters computed by the SOS Cep&RRL pipeline</td></tr><tr><td>Table name</td><td>gaiadr3_vari_rrlyrae</td></tr><tr><td>Source ID</td><td>source_id</td></tr><tr><td>Type</td><td>best_classification (one of RRc, RRab or RRd)</td></tr><tr><td>Pf, P10</td><td>p_f, p1_o</td></tr><tr><td>σ(Pf, P10)</td><td>pf_error, p1_o_error</td></tr><tr><td>E <sup>(a)</sup>(G, G<sub>BP</sub>, G<sub>RP</sub>, RV)</td><td>epoch_g, epoch bp, epoch rp, epoch rv</td></tr><tr><td>σE(G, G<sub>BP</sub>, G<sub>RP</sub>, RV)</td><td>epoch_g_error, epoch bp_error, epoch rp_error, epoch rv_error</td></tr><tr><td>⟨G⟩, ⟨G<sub>BP</sub⟩⟩, ⟨G<sub>RP</sub⟩⟩, ⟨RV⟩</td><td>int_average_g, int_average bp, int_average rp, average rv</td></tr><tr><td>σ⟨G⟩, σ⟨G<sub>BP</sub⟩⟩, σ⟨G<sub>RP</sub⟩⟩, σ⟨RV⟩</td><td>int_average_g_error, int_average bp_error, int_average rp_error, average rv_error</td></tr><tr><td>Amp(G, G<sub>BP</sub>, G<sub>RP</sub>, RV)</td><td>peak_to_peak_g, peak_to_peak bp, peak_to_peak rp, peak_to_peak rv</td></tr><tr><td>σ[Amp(G)], σ[Amp(G<sub>BP</sub>), σ[Amp(G<sub>RP</sub>), σ[Amp(RV)]</td><td>peak_to_peak_g_error, peak_to_peak bp_error, peak_to_peak rp_error, peak_to_peak rv_error</td></tr><tr><td>φ<sub>21</sub>(G)</td><td>phi21_g</td></tr><tr><td>σ[φ<sub>21</sub>(G)]</td><td>phi21_g_error</td></tr><tr><td>R<sub>21</sub>(G)</td><td>r21_g</td></tr><tr><td>σ[R<sub>21</sub>(G)]</td><td>r21_g_error</td></tr><tr><td>φ<sub>31</sub>(G)</td><td>phi31_g</td></tr><tr><td>σ[φ<sub>31</sub>(G)]</td><td>phi31_g_error</td></tr><tr><td>R<sub>31</sub></td><td>r31_g</td></tr><tr><td>σ[R<sub>31</sub>(G)]</td><td>r31_g_error</td></tr><tr><td>[Fe/H] <sup>(b)</sup></td><td>metallicity</td></tr><tr><td>σ([Fe/H])</td><td>metallicity_error</td></tr><tr><td>A(G) <sup>(c)</sup></td><td>g_absorption</td></tr><tr><td>σ A(G)</td><td>g_absorption_error</td></tr><tr><td>N<sub>obs</sub>(G band)</td><td>num_clean_epochs_g</td></tr><tr><td>N<sub>obs</sub>(G<sub>BP</sub> band)</td><td>num_clean_epochs bp</td></tr><tr><td>N<sub>obs</sub>(G<sub>RP</sub> band)</td><td>num_clean_epochs rp</td></tr><tr><td>N<sub>obs</sub>(RV)</td><td>num_clean_epochs rv</td></tr></tbody></table>

**Notes.** Pulsation characteristics include period(s), epochs of maximum light and minimum radial velocity (E), peak-to-peak amplitudes, intensity-averaged mean magnitudes, mean radial velocity, $\phi_{21}$, $R_{21}$, $\phi_{31}$, $R_{31}$ Fourier parameters with related uncertainties. To facilitate access to the table, we also provide the correspondence between parameter [period(s), E, etc.] and the name of the parameter in the Gaia archive table. <sup>(a)</sup>E corresponds to the time of maximum in the light curve and the time of minimum in the RV curve. The BJD of all epochs is offset by JD 2455197.5 d (= J2010.0). <sup>(b)</sup>Photometric metal abundance derived from the period and the $\phi_{31}$ Fourier parameter of the G light curve of RR Lyrae stars (see Sects. 5.1 and 7). <sup>(c)</sup>Absorption in the G band computed from a relation that links the star intrinsic colour to the period and the amplitude of the G-band light variation of fundamental-mode RR Lyrae stars (see Sects. 5.3 and 7).

theoretical models by Marconi et al. (2015). The RR Lyrae stars nicely fall within the boundaries of the theoretical ISs shown in Fig. 29. The slight discrepancy at the red boundary of the IS between observed RR Lyrae position and the predicted edge might be due to the treatment of convection. As extensively discussed in Di Criscienzo et al. (2004), an increase in the mixing-length parameter from the adopted 1.5 value to 2.0 makes the predicted boundary bluer by about 300 K, which matches the observed stellar distribution far better. We also note that the errors of the SOS metallicity estimates of the few RR Lyrae stars with $(G_{BP}-G)$ colours higher than ~0.3 mag that fall outside the red boundaries of the Z = 0.001 and 0.02 ISs are larger than 0.46 and up to 1.5 dex.

## 7.3. Sky maps

Figure 30 shows the distribution on sky in galactic coordinates of the clean sample of 270 905 DR3 RR Lyrae stars, and Fig. 31 shows their PA, $\phi_{21}$ versus P and $\phi_{31}$ versus P diagrams. The two extended RR Lyrae overdensities in the bottom right quadrant of Fig. 30 trace the haloes of the Large and Small Magellanic Clouds. The stream of RR Lyrae stars that crosses the Galactic disc is the disrupting Sagittarius dSph galaxy that becomes visible just left below of the centre of the map. Other lower RR Lyrae overdensities can easily be recognised, for example the Sculptor dSph (with more than 500 RR Lyrae) close to the south Galactic pole, Ursa Minor and Draco dSphs in the upper north-west

quadrant, the Sextans dSph in the upper north-east quadrant, and close to the north Galactic pole the concentration of more than 150 RR Lyrae stars of the M3 GC. About 1500 other RR Lyrae stars are concentrated in another 94 different GCs in the map.

The DR3 RR Lyrae clean catalogue contains 70 611 new RR Lyrae stars discovered by Gaia. They are mainly faint sources (see Fig. 27), and according to Fig. 32, they are mainly concentrated in high-reddening regions of the Galactic disc and bulge that were poorly sampled with the Gaia DR2 scanning law.

Figure 33 presents a map in galactic coordinates that is drawn from 133 559 RR Lyrae stars in the DR3 clean catalogue for which individual photometric metallicities ([Fe/H]) obtained with the SOS Cep&RRL pipeline (see Sect. 5.1) are published in the Gaia DR3 vari_rrlyrae table. We colour-coded the sources in the map according to their metallicity. The higher metallicity of the RR Lyrae stars in the MW bulge and disc compared to variables in the Galactic halo can easily be appreciated, and the lower metal abundance of the RR Lyrae stars in the SMC compared to the variables in the LMC is also clear. To ensure that the features in Fig. 33 are not an artefact due to measurement errors or to the adopted metallicity calibration (Nemec et al. 2013), we show in Fig. 34 only RR Lyrae stars with metallicity errors $\sigma_{[Fe/H]} \le 0.46$ dex (the mean error of the SOS Cep&RRL metallicity estimates according to Fig. 19 in Sect. 5.1). The relative difference in metallicity of the RR Lyrae stars in the LMC, SMC, Galactic halo, and in the bulge and thin disc of our Galaxy is still rather clearly visible, and it would
<table><caption>**Table 12.** Links to the Gaia archive table to retrieve pulsation characteristics, metallicity, and absorption in the G band computed by the SOS Cep&RRL pipeline for 270 891 confirmed RR Lyrae stars (and for 888 rejected sources listed in Table 9) that are released in Gaia DR3.</caption><thead><tr><th>Table URL</th><th>https://gea.esac.esa.int/archive/</th></tr></thead><tbody><tr><td colspan="2">RR Lyrae main parameters computed by the SOS Cep&RRL pipeline</td></tr><tr><td>Table name</td><td>gaiadr3_vari_rrlyrae</td></tr><tr><td>Source ID</td><td>source_id</td></tr><tr><td>Type</td><td>best_classification (one of RRc, RRab or RRd)</td></tr><tr><td>Pf, P10</td><td>p_f, p1_o</td></tr><tr><td>σ(Pf, P10)</td><td>pf_error, p1_o_error</td></tr><tr><td>E <sup>(a)</sup>(G, G<sub>BP</sub>, G<sub>RP</sub>, RV)</td><td>epoch_g, epoch bp, epoch rp, epoch rv</td></tr><tr><td>σE(G, G<sub>BP</sub>, G<sub>RP</sub>, RV)</td><td>epoch_g_error, epoch bp_error, epoch rp_error, epoch rv_error</td></tr><tr><td>⟨G⟩, ⟨G<sub>BP</sub⟩⟩, ⟨G<sub>RP</sub⟩⟩, ⟨RV⟩</td><td>int_average_g, int_average bp, int_average rp, average rv</td></tr><tr><td>σ⟨G⟩, σ⟨G<sub>BP</sub⟩⟩, σ⟨G<sub>RP</sub⟩⟩, σ⟨RV⟩</td><td>int_average_g_error, int_average bp_error, int_average rp_error, average rv_error</td></tr><tr><td>Amp(G, G<sub>BP</sub>, G<sub>RP</sub>, RV)</td><td>peak_to_peak_g, peak_to_peak bp, peak_to_peak rp, peak_to_peak rv</td></tr><tr><td>σ[Amp(G)], σ[Amp(G<sub>BP</sub>), σ[Amp(G<sub>RP</sub>), σ[Amp(RV)]</td><td>peak_to_peak_g_error, peak_to_peak bp_error, peak_to_peak rp_error, peak_to_peak rv_error</td></tr><tr><td>φ<sub>21</sub>(G)</td><td>phi21_g</td></tr><tr><td>σ[φ<sub>21</sub>(G)]</td><td>phi21_g_error</td></tr><tr><td>R<sub>21</sub>(G)</td><td>r21_g</td></tr><tr><td>σ[R<sub>21</sub>(G)]</td><td>r21_g_error</td></tr><tr><td>φ<sub>31</sub>(G)</td><td>phi31_g</td></tr><tr><td>σ[φ<sub>31</sub>(G)]</td><td>phi31_g_error</td></tr><tr><td>R<sub>31</sub></td><td>r31_g</td></tr><tr><td>σ[R<sub>31</sub>(G)]</td><td>r31_g_error</td></tr><tr><td>[Fe/H] <sup>(b)</sup></td><td>metallicity</td></tr><tr><td>σ([Fe/H])</td><td>metallicity_error</td></tr><tr><td>A(G) <sup>(c)</sup></td><td>g_absorption</td></tr><tr><td>σ A(G)</td><td>g_absorption_error</td></tr><tr><td>N<sub>obs</sub>(G band)</td><td>num_clean_epochs_g</td></tr><tr><td>N<sub>obs</sub>(G<sub>BP</sub> band)</td><td>num_clean_epochs bp</td></tr><tr><td>N<sub>obs</sub>(G<sub>RP</sub> band)</td><td>num_clean_epochs rp</td></tr><tr><td>N<sub>obs</sub>(RV)</td><td>num_clean_epochs rv</td></tr></tbody></table>

**Notes.** Pulsation characteristics include period(s), epochs of maximum light and minimum radial velocity (E), peak-to-peak amplitudes, intensity-averaged mean magnitudes, mean radial velocity, $\phi_{21}$, $R_{21}$, $\phi_{31}$, $R_{31}$ Fourier parameters with related uncertainties. To facilitate access to the table, we also provide the correspondence between parameter [period(s), E, etc.] and the name of the parameter in the Gaia archive table. <sup>(a)</sup>E corresponds to the time of maximum in the light curve and the time of minimum in the RV curve. The BJD of all epochs is offset by JD 2455197.5 d (= J2010.0). <sup>(b)</sup>Photometric metal abundance derived from the period and the $\phi_{31}$ Fourier parameter of the G light curve of RR Lyrae stars (see Sects. 5.1 and 7). <sup>(c)</sup>Absorption in the G band computed from a relation that links the star intrinsic colour to the period and the amplitude of the G-band light variation of fundamental-mode RR Lyrae stars (see Sects. 5.3 and 7).

theoretical models by Marconi et al. (2015). The RR Lyrae stars nicely fall within the boundaries of the theoretical ISs shown in Fig. 29. The slight discrepancy at the red boundary of the IS between observed RR Lyrae position and the predicted edge might be due to the treatment of convection. As extensively discussed in Di Criscienzo et al. (2004), an increase in the mixing-length parameter from the adopted 1.5 value to 2.0 makes the predicted boundary bluer by about 300 K, which matches the observed stellar distribution far better. We also note that the errors of the SOS metallicity estimates of the few RR Lyrae stars with $(G_{BP}-G)$ colours higher than ~0.3 mag that fall outside the red boundaries of the Z = 0.001 and 0.02 ISs are larger than 0.46 and up to 1.5 dex.

## 7.3. Sky maps

Figure 30 shows the distribution on sky in galactic coordinates of the clean sample of 270 905 DR3 RR Lyrae stars, and Fig. 31 shows their PA, $\phi_{21}$ versus P and $\phi_{31}$ versus P diagrams. The two extended RR Lyrae overdensities in the bottom right quadrant of Fig. 30 trace the haloes of the Large and Small Magellanic Clouds. The stream of RR Lyrae stars that crosses the Galactic disc is the disrupting Sagittarius dSph galaxy that becomes visible just left below of the centre of the map. Other lower RR Lyrae overdensities can easily be recognised, for example the Sculptor dSph (with more than 500 RR Lyrae) close to the south Galactic pole, Ursa Minor and Draco dSphs in the upper north-west

quadrant, the Sextans dSph in the upper north-east quadrant, and close to the north Galactic pole the concentration of more than 150 RR Lyrae stars of the M3 GC. About 1500 other RR Lyrae stars are concentrated in another 94 different GCs in the map.

The DR3 RR Lyrae clean catalogue contains 70 611 new RR Lyrae stars discovered by Gaia. They are mainly faint sources (see Fig. 27), and according to Fig. 32, they are mainly concentrated in high-reddening regions of the Galactic disc and bulge that were poorly sampled with the Gaia DR2 scanning law.

Figure 33 presents a map in galactic coordinates that is drawn from 133 559 RR Lyrae stars in the DR3 clean catalogue for which individual photometric metallicities ([Fe/H]) obtained with the SOS Cep&RRL pipeline (see Sect. 5.1) are published in the Gaia DR3 vari_rrlyrae table. We colour-coded the sources in the map according to their metallicity. The higher metallicity of the RR Lyrae stars in the MW bulge and disc compared to variables in the Galactic halo can easily be appreciated, and the lower metal abundance of the RR Lyrae stars in the SMC compared to the variables in the LMC is also clear. To ensure that the features in Fig. 33 are not an artefact due to measurement errors or to the adopted metallicity calibration (Nemec et al. 2013), we show in Fig. 34 only RR Lyrae stars with metallicity errors $\sigma_{[Fe/H]} \le 0.46$ dex (the mean error of the SOS Cep&RRL metallicity estimates according to Fig. 19 in Sect. 5.1). The relative difference in metallicity of the RR Lyrae stars in the LMC, SMC, Galactic halo, and in the bulge and thin disc of our Galaxy is still rather clearly visible, and it would
<figure><img src="image_26.png" /><figcaption>**Fig. 28.** CMDs in apparent *G* magnitude vs. ($G_{BP} - G_{RP}$) colour defined by RR Lyrae stars in the DR3 clean catalogue. Left panel: *G* and $G_{BP} - G_{RP}$ CMD of RR Lyrae stars in the DR3 clean catalogue that lie in GCs (red points) and dSph galaxies (blue points), for which colour information is available (2558 out of 2790 sources). Each concentration of points corresponds to a different system. Middle panel: *G* and $G_{BP} - G_{RP}$ CMD of the whole sample of RR Lyrae stars for which colour information is available, 215 116 sources (out of 270 905). Different colours show the variable stars in the LMC (26 468 sources; cyan symbols), SMC (4353 sources; yellow symbols), and all-sky (184 280 sources; grey symbols) regions as defined in Sect. 2. Right panel: lower panel same as in the middle panel, but blue, green, and red points mark RR Lyrae stars with $\sigma_{\omega}/\bar{\omega} < 0.5$ (58 018 sources), $<0.2$ (13 377 sources), and $<0.1$ (4670 sources), respectively.</figcaption></figure>

<figure><img src="image_27.png" /><figcaption>**Fig. 29.** HR diagram in *G* absolute magnitude ($M_{G0}$) and dereddened ($G_{BP} - G_0$) colour. Left panel: $M_{G0}$ ($G_{BP}-G_0$) CMD of 915 DR3 RRab stars that have $\sigma_{\omega}/\bar{\omega} < 0.1$, RUWE < 1.4, and $A(G) < 0.2$; right panel: same as in the left panel, but for 620 RR Lyrae of the sample for which $A(G) < 0.1$. The sources are colour-coded according to their metallicity. The lines show the boundaries of theoretical ISs for RRab stars of three different chemical compositions ($Z = 0.0001$, solid lines; $Z = 0.001$, dashed lines; and $Z = 0.02$, dotted lines) from Marconi et al. (2015).</figcaption></figure>

not change significantly if we were to adopt the Crestani et al. (2021) metallicity calibration, for instance. Figure 35 shows the PA diagram of the 133 559 RR Lyrae stars with a metallicity estimate. We again colour-coded the sources according to their metal abundance. The colour-coding highlights the difference in metallicity of the various sequences (Oosterhoff loci, Oosterhoff 1939) seen in the PA diagram, in particular the higher metallicity of short-period RRab and RRc stars compared to the lower metal abundance of long-period fundamental-mode and first-overtone RR Lyrae.

Finally, we show in Fig. 36 a map in galactic coordinates of 142 660 fundamental-mode RR Lyrae stars with absorption

in the *G*-band computed with the SOS pipeline (see Sect. 5.3). The sources are colour-coded according to their individual $A(G)$ values. They neatly trace the high-extinction regions along the Galactic plane.

## 8. Conclusions and future developments

The factor two in statistics with respect to DR2, the better characterisation of the RR Lyrae stars and their pulsational and astrophysical parameters, along with the improved astrometry published with Gaia EDR3 (Gaia Collaboration 2021) make the SOS Cep&RRL DR3 sample the largest, most homogeneous, and
<figure><img src="image_27.png" /><figcaption>**Fig. 28.** CMDs in apparent *G* magnitude vs. ($G_{BP} - G_{RP}$) colour defined by RR Lyrae stars in the DR3 clean catalogue. Left panel: *G* and $G_{BP} - G_{RP}$ CMD of RR Lyrae stars in the DR3 clean catalogue that lie in GCs (red points) and dSph galaxies (blue points), for which colour information is available (2558 out of 2790 sources). Each concentration of points corresponds to a different system. Middle panel: *G* and $G_{BP} - G_{RP}$ CMD of the whole sample of RR Lyrae stars for which colour information is available, 215 116 sources (out of 270 905). Different colours show the variable stars in the LMC (26 468 sources; cyan symbols), SMC (4353 sources; yellow symbols), and all-sky (184 280 sources; grey symbols) regions as defined in Sect. 2. Right panel: lower panel same as in the middle panel, but blue, green, and red points mark RR Lyrae stars with $\sigma_{\omega}/\bar{\omega} < 0.5$ (58 018 sources), $<0.2$ (13 377 sources), and $<0.1$ (4670 sources), respectively.</figcaption></figure>

<figure><img src="image_28.png" /><figcaption>**Fig. 29.** HR diagram in *G* absolute magnitude ($M_{G0}$) and dereddened ($G_{BP} - G$)$_0$ colour. Left panel: $M_{G0}$ ($G_{BP} - G$)$_0$ CMD of 915 DR3 RRab stars that have $\sigma_{\omega}/\bar{\omega} < 0.1$, RUWE < 1.4, and $A(G) < 0.2$; right panel: same as in the left panel, but for 620 RR Lyrae of the sample for which $A(G) < 0.1$. The sources are colour-coded according to their metallicity. The lines show the boundaries of theoretical ISs for RRab stars of three different chemical compositions ($Z = 0.0001$, solid lines; $Z = 0.001$, dashed lines; and $Z = 0.02$, dotted lines) from Marconi et al. (2015).</figcaption></figure>

not change significantly if we were to adopt the Crestani et al. (2021) metallicity calibration, for instance. Figure 35 shows the PA diagram of the 133 559 RR Lyrae stars with a metallicity estimate. We again colour-coded the sources according to their metal abundance. The colour-coding highlights the difference in metallicity of the various sequences (Oosterhoff loci, Oosterhoff 1939) seen in the PA diagram, in particular the higher metallicity of short-period RRab and RRc stars compared to the lower metal abundance of long-period fundamental-mode and first-overtone RR Lyrae.

Finally, we show in Fig. 36 a map in galactic coordinates of 142 660 fundamental-mode RR Lyrae stars with absorption

in the *G*-band computed with the SOS pipeline (see Sect. 5.3). The sources are colour-coded according to their individual $A(G)$ values. They neatly trace the high-extinction regions along the Galactic plane.

## 8. Conclusions and future developments

The factor two in statistics with respect to DR2, the better characterisation of the RR Lyrae stars and their pulsational and astrophysical parameters, along with the improved astrometry published with Gaia EDR3 (Gaia Collaboration 2021) make the SOS Cep&RRL DR3 sample the largest, most homogeneous, and