dataesr/scientific-paragraphs-categorization huggingface dataset:
Acknowledgments: We are grateful to  CNES  and  DLR  who selected MERLIN in 2010 as a future climate mission based on a dedicated Lidar instrument for the measurement of atmospheric methane for the first time. Special thanks are given to the members of  MERLIN  project teams from  French CNES  ( Carole Deniel ,  Frédéric Estève ,  Eric Julien ,  Jordi Chinaud ,  Caroline Bès ,  Francesc Tintó ,  Pascale Moro ,  Clémence Le Fèvre ,  Etienne Montagnon ,  David Ducros ), from  French LMD  ( Raymond Armante ,  Vincent Cassé ,  Olivier Chomette ,  Dimitri Edouart ,  Ha Tran ,  Thibault Delahaye ,  Jean-Michel Hartmann ,  Yoann Tellier ,  Sébastien Berthier ), from  French groupe de spectrométrie moléculaire et atmosphérique (GSMA)  ( Virginie Zeninari ,  Raphael Vallon ,  Bertrand Parvitte ), from  French  small and medium-sized enterprises (SMEs):  NOVELTIS (Cédric Bacour) ,  CAPGEMINI (Fabien Marnas) ,  MAGELLIUM  ( Emmanuel Hillairet, Frédéric Nahan ),  SYNERGIE (Antonin Deville ), from  DLR Raumfahrtmanagement  ( Achim Friker ,  Dominik Maxein ,  Inés Usandizaga , and  Hermann Berg ,  Christian Stephan ),  DLR Institut für Physik der Atmosphäre  ( Axel Amediek ,  Mathieu Quatrevalet ,  Christoph Kiemle ),  DLR   Institut für Methodik der Fernerkundung  ( Thomas Trautmann ,  Günter Lichtenberg ,  Mourad Hamidouche ),  Deutsches Fernerkundungsdatenzentrum of DLR  ( Erhard Diedrich ,  Stephan Kiemle ,  Kai Wendlandt ), and  Airbus Defence and Space in France  and  Germany  with their suppliers, who all strongly support the mission development during the subsequent phases.
7). They overlap with the reference pre-main sequence RAVE stars often displaying X-ray emission. The activity level increasing with the color reveals their different nature from the solar-like stars and probably represents an underlying dynamo generating magnetic fields in cool stars. 50% of the RAVE objects from DR5 are found in the TGAS catalog and supplemented with accurate parallaxes and proper motions by Gaia. This makes the database of a large number of young stars in a combination with RAVE's radial velocities directly useful as a tracer of the very recent large-scale star formation history in the Solar neighborhood. The data are available online in the Vizier database.
2012, hereafter M12)  tens of thousands of candidate active stars have been uncovered. A large catalog of 44,000 candidate chromospherically active RAVE stars described in the first paper in the series  ( Žerjal et al. 2013, hereafter Z13)  contains over 14,000 stars above the 2σ excess emission detection limit. Around 65% of all the objects in the RAVE database (and 60% of the active candidates) are also found in the Tycho-2 astrometric catalog  (Høg et al. 2000). Because these dwarfs reside in the Solar neighborhood their distance errors in the first Gaia data release (TGAS: "using the positions from the Tycho-2 Catalog as additional information for a joint solution with early Gaia data";  Michalik et al. 2015)  are expected to be of the order of 10%, a number that will become considerably more precise with future data releases (reaching a level of ∼ 1%, e.
g. ,  Bailer-Jones et al. 2013). The catalog of active stars in combination with radial velocities (provided by RAVE) and reliable distances and proper motions will directly enable the study of the early stellar evolution and recent star formation history in the local neighborhood. The dataset will be significantly enhanced by the Gaia-RVS catalog (Radial Velocity Spectrometer, covering the same Ca II IRT domain,  Katz et al. 2004; Cropper & Katz 2011). By the end of the mission the set of around 9 million stars (with their G RV S magnitude brighter than ∼ 11. 75 and the signal-to-noise ratio of their spectra over 20 per pixel) will be the largest database to look for active stars in. In paper I (Z13) we listed our selection of candidate active stars, in the present paper II we derive their ages.
IMPROVED CATALOG The catalog of candidate active stars used in this work is described in detail by Z13. Here we very briefly review the determination of activity levels and basic characteristics of the sample to allow the reader to better understand the context of present study. Chromospheric activity in the RAVE domain manifests itself in an excessive emission flux in the Ca II IRT while the rest of the spectrum remains indistinguishable from an inactive state. The strength of the emission can range from marginally detectable levels to individual cases with fluxes above the continuum level. The qualitative classification of the RAVE database using the locally linear embedding (LLE) technique (M12) entirely based on normalized spectra revealed over 44,000 stars with the possible presence of an excessive emission in the Ca II IRT.
For the detailed selection criteria see Z13. The photospheric component of the flux was eliminated from the active candidate star by the subtraction of the best-matching inactive template spectrum. For the purpose of the spectral subtraction technique a database of over 12,000 inactive single solar-like or latertype main sequence dwarfs with no emission or any other peculiarities was built from the measured RAVE sample. Although chromospheric activity has been detected in evolved stars (e. g. Wilson 1976 ), objects with log g < 3. 5 were excluded from the inactive sample because magnetic activity is not expected to be notably present in giant stars above the main sequence. Rutten 1984 (hereafter R84)  showed that the emission rate in evolved stars is very close to the basal level. The number of stars in the inactive set is sufficient to cover the entire parameter space of active candidates, -Time variability of the Ca II IRT chromospheric emission for stars with multiple measurements measured as the difference between the maximal and minimal activity rate.
Due to lack of inactive stars above the main-sequence the same database of 12,000 stars is used for the activity estimation of the pre-main sequence stars. The advantage of the approach using the measured inactive library from the RAVE Survey in contrast to a synthetic dataset is the fact that active and inactive sets share the same instrumental profile of the spectra (e. g. resolving power and point-spread function along the spectra). It avoids problems with an invalid assumption of the local thermodynamic equilibrium in the chromospheric layer used in models which affects the cores of the strongest lines that are at the same time sensitive to magnetic activity. Moreover, the determination of the best-matching templates is parameter-free because it is based solely on the comparison of the normalized fluxes of active and inactive spectra.
For reference, activity of the inactive database was estimated using the same method. The distribution of equivalent widths in the latter case is centred at -0. 05 Å with a standard deviation of σ = 0. 16 Å. An investigation of the subtracted spectra revealed that their average value outside calcium lies slightly below zero (∼ 10 -3 in the normalized flux units) which translates to the negative offset of the emission equivalent width. σ is accepted as an internal error on the derived EW IRT. Another contribution to the uncertainty is the intrinsic time variability of the activity on the scales of days (stellar flares), months (starspot rotation) and decades (Solar 11-year cycle analogues). The statistics of the repeated observations of the same active stars from the active RAVE catalog (1146 stars, of which 30% were observed more than twice) shows that the median difference between the minimum and maximum values of activity for a single star (EW max IRT -EW min IRT ) is 0.
75, proper motions and radial velocities show no other peculiarities with respect to similar regions at the same Galactic latitude. The ratio between red (J -K ≥ 0. 7) active stars and all red RAVE dwarfs in Aquarius is at least 80%. The same is true for stars with EW IRT ≥ 1 Å. For this reason the Aquarius fields notably contribute to the statistics of the reddest active stars which are otherwise underpopulated in the RAVE sample due to their low luminosities. The selection of candidates in the catalog is based on the set of morphological flags produced by the spectral classification technique. The classification algorithm compares the flux of the spectrum in question with fluxes from the reference database. The reference database was set up in the process involving a locally linear embedding (LLE).
For the details about the key steps see M12 or  Roweis & Saul (2000) ;  Vanderplas & Connolly (2009)  and references therein. The classification of the RAVE data was broken down into two crucial steps. First, a reference database of the most representative ∼ 5000 spectra was established by iteratively sifting the most dense areas of the LLE projection containing the most populated groups of stars. This way all distinct classes of objects were represented as evenly as possible in the final dataset. The reference set was then manually assigned classification flags of 11 distinct morphological classes. The classification of the rest of the RAVE spectra was calculated in the second step by comparing the spectra to the reference set. The outcome for each spectrum is a list of 20 flags ordered by the distance between the flux and its nearest reference neighbors.
For more details see M12. A star was selected as an active candidate when at least one nearest neighbor within its first 6 neighbors from the LLE reference database showed an emissiontype spectrum. While this relatively loose criterion helps to unravel marginally active spectra, it on the other hand contaminates the catalog with individual peculiar stars (where some of their nearest neighbors show unsuitable morphology, e. g. , binaries, giants etc. ). The aim of an improved activity identification is thus the elimination of active candidates that show peculiarity other than an excess emission in the Ca II IRT. The search for such stars was performed in a few independent ways including nearest neighbor investigation, morphology notes and spectral types from the Simbad database and visual spectral inspection of the most active stars with manual elimination besides manual exclusion of stars with inadequate atmospheric parameters.
LLE e denotes stars with no emission-type neighbors (a few 100 stars). These stars were originally included in the catalog because they are candidate members of young clusters and were tested for possibly overlooked emission, especially for cases with a faulty radial velocity shift of several 100 km s -1 due to very strong emission. They were removed from the sample because they do not meet the LLE selection criteria. A cross-check using the online Simbad database for stars with available morphology types (25,238 objects) confirmed the presence of binaries, Miras (marked as 'LLE t, LLE p, J -K > 0. 6' in the table), Cepheids, galaxies (34 cases; most objects are actually stars with galaxies located nearby within 1 arcsec), stars of BY Dra, RS CVn and RR Lyr type, 9 (micro)lensing events, red giant branch and carbon stars, gamma-ray sources and 2 stars of an unknown nature.
The frequency of peculiar Simbad morphology types is less than 3%. Note that spectra of RS CVn-type stars can look identical to active single stars and BY Dra stars can mimic chromospheric activity. Because the frequency of such known stars in the active sample is relatively small (13 RS CVn and 28 BY Dra objects) it is assumed that only a few individual cases could be left unrecognised in the database. Simbad spectral types ('SimbadSpType') available for 4691 stars uncovered B, A and F-types and giants (lumi-nosity classes I, II and III). The rest of the spectra has a clear peak on the main sequence: most of the stars are G-and K-type dwarfs. 9138 stars were removed in total from the initial catalog. A list of the number of stars meeting either of the rejection criteria described above is given in Table  1.
Because each active spectrum was compared to its nearest neighbor (and not to an averaged inactive spectrum) the fact that the least active spectra lie within 1 or 2σ bands does not necessarily mean that they do not differ from their inactive counterpart. For the most active spectra line asymmetries (towards red) appear. An averaged spectrum in the decontaminated catalog together with 1 and 2 σ flux variations is compared with the averaged spectrum from the inactive database in Fig-  ure 4. The main contribution to the variations is a range of different atmospheric temperatures (see Sec. 3 for further discussion) and noise. The average 1 σ variation of the continuum parts is ∼ 0. 02 in the middle and ∼ 0. 03 at the very ends of the spectrum. The value is consistent with the signal-to-noise estimation.
2 Å and 3. 4 Å and 2 stars between EW IRT = 3. 4 Å and 3. 6 Å. ) Besides calcium lines, a mismatch between the averaged inactive and active spectrum occurs in other strong lines because the active database consists of cooler stars than the inactive dataset (see Sec. 3 for the comparison). Our new improved catalog of active candidates includes 38,678 spectra of 35,750 stars. Within the sample, the emission levels of 21,925 stars exceed EW IRT = 0. 1 Å (1 σ) and the activity of almost 13,000 stars surpasses the 2 σ emission detection level. The distribution of activity is clearly bimodal (Fig. 5 ). A question arises whether the more active peak at ∼ 1. 5 Å is an evident feature or simply a tail of the inactive distribution enhanced by the logarithmic scale on the plot. A comparison of the expected fraction of stars (a single Gaussian distribution centered at -0.
05 Å and with σ = 0. 16 Å that corresponds to the inactive sample) and the actual fraction of and the expected number Nexp. for the unimodal Gaussian distribution with the average of -0. 05 Å and σ = 0. 16 Å (these are parameters for the inactive database activity distribution). The ratio N/Nexp. shows that the number of active stars largely exceeds the expected number from the unimodal distribution. This is quantitative evidence for the bimodality of the distribution of active stars. 2 ) strongly supports the hypothesis of the bimodal distribution. The less active peak is composed of stars with undetectable emission and a moderately active group of stars above EW IRT = 0. 1 Å. Its skewness does not originate in the imposed tail of the more active peak but stands on its own: the amplitude of the more active peak is ∼ 100 but at EW IRT = 0.
COLORS OF ACTIVE STARS Besides the 2MASS J and K s magnitudes  (Cutri et al. 2003 ; 94% of J magnitude uncertainties and 96% of K magnitude uncertainties below 0. 03 mag for active RAVE stars) additional data were acquired to better characterize the nature of emission objects. The catalog is supplemented by N UV fluxes from the GALEX Survey  (Bianchi et al. 2011 ; 1771-2831 Å; 50% of stars with uncertainties below 0. 04 mag and 80% below 0. 1 mag), the ROSAT X-ray flux data (0. 1-2. 4 keV;  Voges et al. 1999) , WISE W 1 and W 2 mid-infrared bandpasses (3. 4 and 4. 6 µm;  Cutri & et al. 2014 ; typical W 1 uncertainties are 0. 023 and typical W 2 uncertainties are 0. 020) and Landolt V magnitudes from the APASS database (typical uncertainties 0. 02 mag;  Henden & Munari 2014). A cross-match between RAVE and the GALEX and the WISE catalogs was performed by the X-match online application (criterion of 5 arcsec radius).
A manual coordinate match was used for the APASS catalog with 3 arcsec as a maximum distance between APASS and RAVE stars (the typical APASS astrometric uncertainty is 0. 17 arcsec, the fibre size in RAVE is 6. 7 arcsec). Xray sources were identified via ROSAT 1RXS names obtained through the Simbad online database. It is likely that many of the sources were overlooked but a direct coordinate match was not reliable due to large positional errors in the ROSAT data (10 arcsec). The J -K colors of the majority of active stars lie between the Solar value (0. 36) and ∼ 0. 7 (Fig. 6 , lower panel) while the inactive database is solar-like. A bump at J -K ∼ 0. 55 in the color distribution of the active sample originates in the fact that a color-cut was performed in the Galactic plane (|b| < 25 • ) at J -K = 0.
What is more, RAVE stars with EW IRT > 1 Å identified in the Simbad database as premain sequence, T Tauri and young objects, together with objects younger than 100 Myr (identification is given in the appendix, Table  6 ), reside in the same active part of the plots. Members of clusters, moving groups and associations are plotted for comparison. The consistency of the photometric data justifies the assumption that the majority of the stars off the main sequence in the N UV -V -J -K and W 1 -W 2 -J -K planes (i. e. very active stars with EW IRT > 1 Å) are very young, possibly still residing on the Hayashi tracks. The sample traces stars originating from recent star formation events in the Solar neighborhood. The reader may recall that active RAVE objects are field stars with a random selection function.
This effect is reduced in the RAVE active catalog with the spectral subtraction technique. However, lower abundances might affect the dynamo itself and the generation of the heating. 6  for references and additional info). Despite many limitations described in the previous section and considerable scatter of the data the large scale correlation between activity and age is still evident in RAVE (Fig. 10 ). It allows us to provide a coarse calibration. The goal of this work is not precise dating but a relation that gives an order of magnitude age estimate that can significantly contribute to the establishment of young candidate lists in large field star surveys. A moving mean of the ages within activity bins (0. 25 Å) up to 2 Å is presented together with the ±1σ deviations in the Table  3. Since this is an approximate relation we assume that more active stars are not older than a few tens of millions of years.
25 Å are estimated to be 1 billion years or greater. Stars with activity levels between 0. 25 and 0. 75 Å are estimated to be between 0. 1 and 1 Gyr old whereas the most active stars (EW IRT ≥ 0. 75 Å) are younger than 100 Myr. Nevertheless, the result is highly beneficial in large surveys for the identification of a large number of young stars that are candidates for further more detailed investigation using alternative methods. The catalog of active stars will appear online in the Vizier database. The description of the columns including the age estimate is given in Table  4.
For this reason the data analysis was performed for three different color ranges. Moreover, active stars were divided into two groups: less active stars with EW IRT < 1 Å and more active stars with EW IRT ≥ 1 Å. Distances for inactive stars are not considered because of the selection criterion: very high signal-to-noise values of template spectra were demanded when building the inactive database which effectively means that these stars must reside very close to the Sun. At 1 Gyr (Fig. 12 , panels d, e and f) more active stars (especially solar-like ones with 0. 2 < J -K < 0. 5, panel d) on average have smaller distances than less active stars. There is no reason for their absence at greater distances. As it is evident that the more active stars might still reside in their pre-main sequence phases, the problem can be solved by raising the most active subset to younger and more luminous isochrones as stellar distance in the Hertzsprung-Russell diagram grows in the direction toward the giants.
Histograms for stars with EW IRT < 1 Å (solid and dotted black line) are shown according to the left axis while the scale for stars with EW IRT ≥ 1 Å (solid and dotted blue and red line) is shown on the right. Distribution of mock-RAVE stars (using the Galaxia model) is shown for comparison (dashed lines; 'young stars' mark sample of objects with ages corresponding to 0. 1 Å < EW IRT < 1 Å, 'very young stars' would show EW IRT > 1 Å at their age. distribution of less active stars reaches greater distances. In order to better understand the distance distribution of the youngest RAVE stars, the population synthesis code Galaxia  (Sharma et al. 2011 ) was used to produce a mock-RAVE catalog  (Wojno et al. 2016). First, a full-sky synthetic catalog was generated with an apparent magnitude limit 0 < I DENIS < 14.
2) and stars with 7. 78 < log age < 9. 23 (0. 1 Å < EW IRT < 1 Å; green line). In order to additionally divide the sample into three color classes the temperature was converted to J -K colors (stars with T eff > 5100 K correspond to J -K < 0. 5, stars with 4500 K < T eff < 5100 K to 0. 5 < J -K < 0. 7 and stars cooler than 4500 K to J -K > 0. 7). A qualitative comparison between the observed and mock catalog distributions shows similar trends. The lack of more distant, very young stars in the bluest sample (0. 2 < J -K < 0. 5, panel d) is also evident in the mock sample. The nonexistence of distant, very young stars in the mock catalog as well excludes the selection effect in the observed RAVE sample. Note that there is a quantitative difference present between the mock and observed dataset.
1 dex  (De Silva et al. 2015)  and with a combination of Hα and Hβ emission looks suitable to help to disentangle the underlying processes. An interesting phenomenon in the distribution of active stars in the EW IRT versus J -K space is observed (Sec. 3). Above J -K > 0. 7, the average activity is not only the highest but correlated with color as well (Fig. 6 ). The contribution of the color-dependent basal emission is excluded from the EW IRT by the spectral subtraction technique using a measured inactive template database. A similar trend is observed in the sample of inactive stars (a small fraction of the coolest marginally active stars was recognized as inactive because of relaxed selection criteria due to the lack of inactive red stars). Further photometric investigation (Fig. 7 ) unveiled their position off the main sequence in both the J -K -N UV -V and J -K -W 1 -W 2 space with exposing a large nearultraviolet and mid-infrared excess emission.
Pre-main 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 J -K 10 -2 10 -1 10 0 Fraction of active stars for given activity rate > 0. 1 > 0. 25 > 0. 5 > 0. 75 > 1 > 1. 5 EW IRT [ Å] Fig. 13. -Probability for any detectable signs of activity present in the RAVE's Ca II IRT above a selected EW IRT treshold for a randomly observed dwarf with the known J -K in the Solar neighborhood within ∼ 300 pc. The ratio of number of active stars above selected activity rate over the number of all RAVE dwarf stars is shown for each color bin. Dotted horizontal lines mark 5, 10, 25 and 50% levels. sequence, T Tauri and young stars together with X-ray sources (additional data from the Simbad database) and stars younger than 100 Myr (see appendix for the age reference) overlap with these regions. Undoubtedly, red and very active stars appear to be extremely young, probably still on their way to the main sequence.
They showed that areas with higher density and activity higher than average in the U -V velocity plane correlate with the known positions of moving groups and clusters. Antoja et al. 2012  detected significant overdensities in the velocity distributions of the RAVE disc stars in and beyond the Solar neighborhood (they report on the main local kinematic groups to be large-scale features surviving at least up to ∼ 1 kpc from the Sun). According to their findings, a large number of young RAVE stars probably belong to known (or possibly still undiscovered) moving groups and recently disrupted clusters. Orbital simulations would provide more detailed insight into this matter. Their photometric distances remain unreliable (Sec. 5), but around 50% of the sample is found in the TGAS catalog. Since the database consists of dwarfs in the Solar neighborhood their parallaxes and proper motions are expected to be derived with high accuracy and precision.