bluuebunny/crossref_metadata_2025_split huggingface dataset:
Minute-cadence Observations of the LAMOST Fields with the TMTS: I. Methodology of Detecting Short-period Variables and Results from the first-year Survey
Authors: Lin Jie , Wang Xiaofeng , Mo Jun , Xi Gaobo , Zhang Jicheng , Jiang Xiaojun , Shi Jianrong , Zhang Xiaobin , Zhang Xiaoming , Wei Zixuan , Ye Limeng , Wu Chengyuan , Yan Shengyu , Chen Zhihao , Li Wenxiong , Li Xue , Lin Weili , Lin Han , Sai Hanna , Xiang Danfeng , Zhang Xinghan 
Published: September 2021

Abstract
Tsinghua University-Ma Huateng Telescopes for Survey (TMTS), located at Xinglong Station of NAOC, has a field of view up to 18 deg2. The TMTS has started to monitor the LAMOST sky areas since 2020, with the uninterrupted observations lasting for about 6 hours on average for each sky area and a cadence of about 1 minute. Here we introduce the data analysis and preliminary scientific results for the first-year observations, which covered 188 LAMOST plates (≈1970 deg2). These observations have generated over 4.9 million uninterrupted light curves, with at least 100 epochs for each of them. These light curves correspond to 4.26 million Gaia-DR2 sources, among which 285 thousand sources are found to have multi-epoch spectra from the LAMOST. By analysing these light curves with the Lomb-Scargle periodograms, we identify more than 3700 periodic variable star candidates with periods below ≈7.5 hours, primarily consisting of eclipsing binaries and δ Scuti stars. Those short-period binaries will provide important constraints on theories of binary evolution and possible sources for space gravitational wave experiments in the future. Moreover, we also identified 42 flare stars by searching rapidly-evolving signals in the light curves. The densely-sampled light curves from the TMTS allow us to better quantify the shapes and durations for these flares.
Preliminary clustering properties of the DESI BGS bright targets using DR9 Legacy Imaging Surveys
Authors: Zarrouk Pauline , Ruiz-Macias Omar , Cole Shaun , Norberg Peder , Baugh Carlton , Brooks David , Gaztañaga Enrique , Kitanidis Ellie , Kehoe Robert , Landriau Martin , Moustakas John , Prada Francisco , Tarlé Gregory 
Published: September 2021

ABSTRACT
We characterize the selection cuts and clustering properties of a magnitude-limited sample of bright galaxies that is part of the Bright Galaxy Survey (BGS) of the Dark Energy Spectroscopic Instrument (DESI) using the ninth data release of the Legacy Imaging Surveys (DR9). We describe changes in the DR9 selection compared to the DR8 one and we also compare the DR9 selection in three distinct regions: BASS/MzLS in the north Galactic Cap (NGC), DECaLS in the NGC, and DECaLS in the south Galactic Cap (SGC). We investigate the systematics associated with the selection and assess its completeness by matching the BGS targets with the Galaxy and Mass Assembly (GAMA) survey. We measure the angular clustering for the overall bright sample (rmag ≤ 19.5) and as function of apparent magnitude and colour. This enables to determine the clustering strength r0 and slope γ by fitting a power-law model that can be used to generate accurate mock catalogues for this tracer. We use a counts-in-cells technique to explore higher order statistics and cross-correlations with external spectroscopic data sets in order to check the evolution of the clustering with redshift and the redshift distribution of the BGS targets using clustering redshifts. While this work validates the properties of the BGS bright targets, the final target selection pipeline and clustering properties of the entire DESI BGS will be fully characterized and validated with the spectroscopic data of Survey Validation.
The high-redshift tail of stellar reionization in LCDM is beyond the reach of the low-ℓ CMB
Authors: Wu Xiaohan , McQuinn Matthew , Eisenstein Daniel , Iršič Vid 
Published: September 2021

ABSTRACT
The first generation (Pop-III) stars can ionize 1–10 per cent of the universe by z = 15, when the metal-enriched (Pop-II) stars may contribute negligibly to the ionization. This low ionization tail might leave detectable imprints on the large-scale CMB E-mode polarization. However, we show that physical models for reionization are unlikely to be sufficiently extended to detect any parameter beyond the total optical depth through reionization. This result is driven in part by the total optical depth inferred by Planck, indicating a reionization midpoint around z = 8, which in combination with the requirement that reionization completes by z ≈ 5.5 limits the amplitude of an extended tail. To demonstrate this, we perform semi-analytic calculations of reionization including Pop-III star formation in minihalos with Lyman-Werner feedback. We find that standard Pop-III models need to produce very extended reionization at z &gt; 15 to be distinguishable at 2-σ from Pop-II-only models, assuming a cosmic variance-limited measurement of the low-ℓ EE power spectrum. However, we show that unless there is a late-time quenching mechanism such as from strong X-ray feedback or some other extreme Pop-III scenario, structure formation makes it quite challenging to produce high enough Thomson scattering optical depth from z &gt; 15, τ(z &gt; 15), and still be consistent with other observational constraints on reionization.
Exploring black hole scaling relations via the ensemble variability of active galactic nuclei
Authors: Georgakakis A , Papadakis I , Paolillo M 
Published: September 2021

ABSTRACT
An empirical model is presented that links, for the first time, the demographics of active galactic nuclei (AGN) to their ensemble X-ray variability properties. Observations on the incidence of AGN in galaxies are combined with (i) models of the power spectrum density (PSD) of the flux variations of AGN and (ii) parametrizations of the black hole mass versus stellar mass scaling relation to predict the mean excess variance of active black hole populations in cosmological volumes. We show that the comparison of the model with observational measurements of the ensemble excess variance as a function of X-ray luminosity provides a handle on both the PSD models and the black hole mass versus stellar mass relation. We find strong evidence against a PSD model that is described by a broken power law and a constant overall normalization. Instead, our analysis indicates that the amplitude of the PSD depends on the physical properties of the accretion events, such as the Eddington ratio and/or the black hole mass. We also find that current observational measurements of the ensemble excess variance are consistent with the black hole mass versus stellar mass relation of local spheroids based on dynamically determined black hole masses. We also discuss future prospects of the proposed approach to jointly constrain the PSD of AGN and the black hole mass versus stellar mass relation as a function of redshift.
Impact of relativistic jets on the star formation rate: a turbulence-regulated framework
Authors: Mandal Ankush , Mukherjee Dipanjan , Federrath Christoph , Nesvadba Nicole P H , Bicknell Geoffrey V , Wagner Alexander Y , Meenakshi Moun 
Published: September 2021

ABSTRACT
We apply a turbulence-regulated model of star formation to calculate the star formation rate (SFR) of dense star-forming clouds in simulations of jet–interstellar medium (ISM) interactions. The method isolates individual clumps and accounts for the impact of virial parameter and Mach number of the clumps on the star formation activity. This improves upon other estimates of the SFR in simulations of jet–ISM interactions, which are often solely based on local gas density, neglecting the impact of turbulence. We apply this framework to the results of a suite of jet–ISM interaction simulations to study how the jet regulates the SFR both globally and on the scale of individual star-forming clouds. We find that the jet strongly affects the multiphase ISM in the galaxy, inducing turbulence and increasing the velocity dispersion within the clouds. This causes a global reduction in the SFR compared to a simulation without a jet. The shocks driven into clouds by the jet also compress the gas to higher densities, resulting in local enhancements of the SFR. However, the velocity dispersion in such clouds is also comparably high, which results in a lower SFR than would be observed in galaxies with similar gas mass surface densities and without powerful radio jets. We thus show that both local negative and positive jet feedback can occur in a single system during a single jet event, and that the SFR in the ISM varies in a complicated manner that depends on the strength of the jet–ISM coupling and the jet break-out time-scale.
Gas-phase formation of cationic fullerene/9-aminoanthracene clusters: an indicator for interstellar dust growth
Authors: Hu Xiaoyi , Zhang Deping , Zhang Congcong , Yang Yuanyuan , Chen Yang , Zhen Junfeng , Qin Liping 
Published: September 2021

ABSTRACT
Growth of clusters by adduction of monomers – as the first step in dust particle growth – is an area of much interest in astronomy. We focus on the fullerene/9-aminoanthracene cluster species, to illustrate the competition between the van der Waals bonding growth and the covalent bonding growth model versus the charge transfer model in the large cluster formation process. The experimental results show that fullerene-fragment (C56 and C58)/9-aminoanthracene cluster cations, e.g. [(C14H11N)nC56]+ and [(C14H11N)nC58]+, n = [1,7], are efficiently formed, while C$_{60}^+$ is insensitive to the cluster’s formation. With laser irradiation, all the fullerene/9-aminoanthracene clusters dissociate into 9-aminoanthracene and fullerene cations. The mechanisms for the reactions of fullerene cations and 9-aminoanthracene were investigated by theoretical calculations, under the assumption that the molecular geometries found for the formed complexes correspond to the global energy minima: the absence of C$_{60}^+$ clusters is mainly due to the charge transfer channel’s competition; [(C14H11N)C58]+ has three types of isomers, with van der Waals or covalent bonds, mainly depending on the reaction sites of fullerene cations. Importantly, in the size grown process, for the fullerene/9-aminoanthracene cluster there exists a geometry configuration conversion between the van der Waals and covalent bonding modes. The largest fullerene/9-aminoanthracene clusters, e.g. [(C14H11N)7C58]+ (240 atoms, ∼4 nm in size), are likely in a multishelled geometry, i.e. seven 9-aminoanthracene molecules surrounding fullerene cations in two layers, which can directly build the relationship between molecular clusters and carbonaceous grains. Nitrogen matters! The specific side chains (e.g. –NH2) play an important role in the growth of interstellar dust.
Molecular gas along the old radio jets of the cluster-central type 2 quasar IRAS 09104+4109
Authors: O’Sullivan Ewan , Combes Françoise , Babul Arif , Chapman Scott , Phadke Kedar A , Schellenberger Gerrit , Salomé Philippe 
Published: September 2021

ABSTRACT
We present Northern Extended Millimeter Array (NOEMA) CO(2–1) maps of the z = 0.4418 cluster-central quasi-stellar object (QSO) IRAS 09104+4109, which trace ∼4.5 × 1010 M⊙ of molecular gas in and around the galaxy. As in many low-redshift cool-core clusters, the molecular gas is located in a series of clumps extending along the old radio jets and lobes. It has a relatively low velocity dispersion [336$^{+39}_{-35}$ km s−1 full width at half-maximum (FWHM)] and shows no velocity gradients indicative of outflow or infall. Roughly half the gas is located in a central clump on the north-east side of the galaxy, overlapping a bright ionized gas filament and a spur of excess X-ray emission, suggesting that this is a location of rapid cooling. The molecular gas is unusually extended, out to ∼55 kpc radius, comparable to the scale of the filamentary nebula in the Perseus cluster, despite the much higher redshift of this system. The extent falls within the thermal instability radius of the intracluster medium (ICM), with tcool/$t_{\rm ff} \lt 25$ and tcool/$t_{\rm eddy} \sim 1$ within ∼70 kpc. Continuum measurements at 159.9 GHz from NOEMA and 850 $\mu$m from the James Clerk Maxwell Telescope (JCMT) Submillimeter Common-User Bolometer Array 2 (SCUBA-2) show excess far-infrared emission, which we interpret as free–free emission arising from the ongoing starburst. These observations suggest that ICM cooling is not strongly affected by the buried QSO, and that cooling from the ICM can build gas reservoirs sufficient to fuel quasar-mode activity and drive the reorientation of the central active galactic nuclei (AGN).
Non-radial modes in classical Cepheids: what to look for in spectroscopy?
Authors: Netzel H , Kolenberg K 
Published: September 2021

ABSTRACT
Recent photometric observations of first-overtone classical Cepheids and RR Lyrae stars have led to the discovery of additional frequencies showing a characteristic period ratio of 0.60–0.65 with the main pulsation mode. In a promising model proposed by Dziembowski (2016), these signals are suggested to be due to the excitation of non-radial modes with degrees 7, 8, and 9 (Cepheids) or 8 and 9 (RR Lyrae). Such modes usually have low amplitudes in photometric data. Spectroscopic time series offer an unexplored and promising way forward. We simulated time series of synthetic line profiles for a representative first-overtone classical Cepheid model and added a low-amplitude non-radial mode. We studied sets of spectra with dense sampling and without noise, so-called ’perfect’ cases, as well as more realistic samplings and signal-to-noise levels. Besides the first-overtone mode and the non-radial mode, also the harmonics of both modes and combination signals were often detected, but a sufficiently high sampling and signal-to-noise ratio prove essential. The amplitudes of the non-radial mode and its harmonic depend on the azimuthal order m. The inclination is also an important factor determining the detectability of the non-radial mode and/or its harmonic. We compared the results obtained for the predicted high degrees with those for lower-degree modes. Finally, we studied the sampling requirements for detecting the non-radial mode. Our findings can be used to plan a spectroscopic observing campaign tailored to uncover the nature of these mysterious modes.
Common-red-signal analysis with 24-yr high-precision timing of the European Pulsar Timing Array: inferences in the stochastic gravitational-wave background search
Authors: Chen S , Caballero R N , Guo Y J , Chalumeau A , Liu K , Shaifullah G , Lee K J , Babak S , Desvignes G , Parthasarathy A , Hu H , van der Wateren E , Antoniadis J , Bak Nielsen A-S , Bassa C G , Berthereau A , Burgay M , Champion D J , Cognard I , Falxa M , Ferdman R D , Freire P C C , Gair J R , Graikou E , Guillemot L , Jang J , Janssen G H , Karuppusamy R , Keith M J , Kramer M , Liu X J , Lyne A G , Main R A , McKee J W , Mickaliger M B , Perera B B P , Perrodin D , Petiteau A , Porayko N K , Possenti A , Samajdar A , Sanidas S A , Sesana A , Speri L , Stappers B W , Theureau G , Tiburzi C , Vecchio A , Verbiest J P W , Wang J , Wang L , Xu H 
Published: September 2021

ABSTRACT
We present results from the search for a stochastic gravitational-wave background (GWB) as predicted by the theory of General Relativity using six radio millisecond pulsars from the Data Release 2 (DR2) of the European Pulsar Timing Array (EPTA) covering a timespan up to 24 yr. A GWB manifests itself as a long-term low-frequency stochastic signal common to all pulsars, a common red signal (CRS), with the characteristic Hellings-Downs (HD) spatial correlation. Our analysis is performed with two independent pipelines, ENTERPRISE, and TEMPONEST+FORTYTWO, which produce consistent results. A search for a CRS with simultaneous estimation of its spatial correlations yields spectral properties compatible with theoretical GWB predictions, but does not result in the required measurement of the HD correlation, as required for GWB detection. Further Bayesian model comparison between different types of CRSs, including a GWB, finds the most favoured model to be the common uncorrelated red noise described by a power law with $A = 5.13_{-2.73}^{+4.20} \times 10^{-15}$ and $\gamma = 3.78_{-0.59}^{+0.69}$ (95 per cent credible regions). Fixing the spectral index to γ = 13/3 as expected from the GWB by circular, inspiralling supermassive black hole binaries results in an amplitude of $A =2.95_{-0.72}^{+0.89} \times 10^{-15}$. We implement three different models, BAYESEPHEM, LINIMOSS, and EPHEMGP, to address possible Solar system ephemeris (SSE) systematics and conclude that our results may only marginally depend on these effects. This work builds on the methods and models from the studies on the EPTA DR1. We show that under the same analysis framework the results remain consistent after the data set extension.
NGC 6124: a young open cluster with anomalous- and fast-rotating giant stars
Authors: Holanda N , Drake N A , Corradi W J B , Ferreira F A , Maia F , Magrini L , da Silva J R P , Pereira C B 
Published: September 2021

ABSTRACT
We present the results of a chemical analysis of fast and anomalous rotator giants members of the young open cluster NGC 6124. For this purpose, we carried out abundances of the mixing sensitive species such as Li, C, N, Na, and 12C/13C isotopic ratio, as well as other chemical species for a sample of four giants among the seven observed ones. This study is based on standard spectral analysis technique using high-resolution spectroscopic data. We also performed an investigation of the rotational velocity ($v\, \sin \, i$) once this sample exhibits abnormal values – giant stars commonly present rotational velocities of few km s−1. In parallel, we have performed a membership study, making use of the third data release from ESA Gaia mission. Based on these data, we estimated a distance of d = 630 pc and an age of 178 Myr through isochrone fitting. After that procedure, we matched all the information raised and investigated the evolutionary stages and thermohaline mixing model through of spectroscopic Teff and $\log \, g$ and mixing tracers, such as 12C/13C and Na, of the studied stars. We derived a low mean metallicity of [Fe/H] = −0.13 ± 0.05 and a modest enhancement of the elements created by the s-process, such as Y, Zr, La, Ce, and Nd, which is in agreement with what has already been reported in the literature for young clusters. The giants analysed have homogeneous abundances, except for lithium abundance [$\log \, \epsilon$(Li)NLTE = 1.08 ± 0.42] and this may be associated with a combination of mechanisms that act increasing or decreasing lithium abundances in stellar atmospheres.
Gravitational fragmentation of extremely metal-poor circumstellar discs
Authors: Shima Kazuhiro , Hosokawa Takashi 
Published: September 2021

ABSTRACT
We study the gravitational fragmentation of circumstellar discs accreting extremely metal-poor ($Z \le 10^{-3}\, \mathrm{Z}_{\odot }$) gas, performing a suite of 3D hydrodynamic simulations using the adaptive mesh refinement code enzo. We systematically follow the long-term evolution for 2 × 103 yr after the first protostar’s birth, for the cases of Z = 0, 10−5, 10−4, and $10^{-3}\, \mathrm{Z}_{\odot }$. We show that evolution of number of self-gravitating clumps qualitatively changes with Z. Vigorous fragmentation induced by dust cooling occurs in the metal-poor cases, temporarily providing ∼10 self-gravitating clumps at Z = 10−5 and $10^{-4}\, \mathrm{Z}_{\odot }$. However, we also show that the fragmentation is a very sporadic process; after an early episode of the fragmentation, the number of clumps continuously decreases as they merge away in these cases. The vigorous fragmentation tends to occur later with the higher Z, reflecting that the dust-induced fragmentation is most efficient at the lower density. At $Z = 10^{-3}\, \mathrm{Z}_{\odot }$, as a result, the clump number stays smallest until the disc fragmentation starts in a late stage. We also show that the clump mass distribution depends on the metallicity. A single or binary clump substantially more massive than the others appear only at $Z = 10^{-3}\, \mathrm{Z}_{\odot }$, whereas they are more evenly distributed in mass at the lower metallicities. We suggest that the disc fragmentation should provide the stellar multiple systems, but their properties drastically change with a tiny amount of metals.
Fractal dimension of optical cirrus in Stripe82
Authors: Marchuk Alexander A , Smirnov Anton A , Mosenkov Aleksandr V , Il’in Vladimir B , Gontcharov George A , Savchenko Sergey S , Román Javier 
Published: September 2021

ABSTRACT
The geometric characteristics of dust clouds provide important information on the physical processes that structure such clouds. One of such characteristics is the 2D fractal dimension D of a cloud projected on to the sky plane. In previous studies, which were mostly based on infrared (IR) data, the fractal dimension of individual clouds was found to be in a range from 1.1 to 1.7 with a preferred value of 1.2–1.4. In this work, we use data from Stripe82 of the Sloan Digital Sky Survey to measure the fractal dimension of the cirrus clouds. This is done here for the first time for optical data with significantly better resolution as compared to IR data. To determine the fractal dimension, the perimeter-area method is employed. We also consider IR (IRAS and Herschel) counterparts of the corresponding optical fields to compare the results between the optical and IR. We find that the averaged fractal dimension across all clouds in the optical is $\langle D \rangle =1.69^{+0.05}_{-0.05}$ which is significantly larger than the fractal dimension of its IR counterparts $\langle D\rangle =1.38^{+0.07}_{-0.06}$. We examine several reasons for this discrepancy (choice of masking and minimal contour level, image and angular resolution, etc.) and find that for approximately half of our fields the different angular resolution (point spread function) of the optical and IR data can explain the difference between the corresponding fractal dimensions. For the other half of the fields, the fractal dimensions of the IR and visual data remain inconsistent, which can be associated with physical properties of the clouds, but further physical simulations are required to prove it.
Testing the consistency of dust laws in SN Ia host galaxies: a BayeSN examination of Foundation DR1
Authors: Thorp Stephen , Mandel Kaisey S , Jones David O , Ward Sam M , Narayan Gautham 
Published: September 2021

ABSTRACT
We apply BayeSN, our new hierarchical Bayesian model for the SEDs of Type Ia supernovae (SNe Ia), to analyse the griz light curves of 157 nearby SNe Ia (0.015 &lt; z &lt; 0.08) from the public Foundation Supernova Survey data set. We train a new version of BayeSN, continuous from 0.35 to 0.95 μm, which we use to model the properties of SNe Ia in the rest-frame z-band, study the properties of dust in their host galaxies, and construct a Hubble diagram of SN Ia distances determined from full griz light curves. Our griz Hubble diagram has a low total RMS of 0.13 mag using BayeSN, compared to 0.16 mag using SALT2. Additionally, we test the consistency of the dust law RV between low- and high-mass host galaxies by using our model to fit the full time- and wavelength-dependent SEDs of SNe Ia up to moderate reddening (peak apparent B − V ≲ 0.3). Splitting the population at the median host mass, we find RV = 2.84 ± 0.31 in low-mass hosts, and RV = 2.58 ± 0.23 in high-mass hosts, both consistent with the global value of RV = 2.61 ± 0.21 that we estimate for the full sample. For all choices of mass split we consider, RV is consistent across the step within ≲ 1.2σ. Modelling population distributions of dust laws in low- and high-mass hosts, we find that both subsamples are highly consistent with the full sample’s population mean μ(RV) = 2.70 ± 0.25 with a 95 per cent upper bound on the population σ(RV) &lt; 0.61. The RV population means are consistent within ≲ 1.2σ. We find that simultaneous fitting of host-mass-dependent dust properties within our hierarchical model does not account for the conventional mass step.