J/A+A/688/A49ivo://CDS.VizieR/J/A+A/688/A49doi:10.26093/cds/vizier.36880049CDSJoseph W.M.Stelzer B.Magaudda E.Vicanek Martinez T.2024-11-29T20:05:03Z2024-08-01T06:48:47ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frm-starsx-ray-sourcesphotometryvisible-astronomyinfrared-photometryeffective-temperatureM-dwarf stars are the most numerous stars in the Galaxy, and are highly magnetically active. They exhibit bursts of radiation and matter, called flares and coronal mass ejections which have the potential to strongly affect the habitability of their planets. We investigate variability through simultaneous optical and X-ray observations, forming the largest statistical sample of M dwarfs observed in this way so far. Such simultaneous observations at different wavelengths, which correspond to emissions from different layers of the stellar atmosphere, are required to constrain the flare frequency and energetics and to understand the physics of flares. We used light curves from the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Russian Spektrum-Roentgen-Gamma mission (SRG) and the Transiting Exoplanet Survey Satellite (TESS) for a sample of M dwarfs observed simultaneously with both instruments. Specifically, we identified 256 M dwarfs in the TESS Southern Continuous Viewing Zone (SCVZ), which corresponds to a sky area of 452.39deg^2^, with simultaneous TESS and eROSITA detection. For this work, we selected the 25 X-ray brightest or most X-ray variable stars. We used photometric data from Gaia and 2MASS to obtain stellar parameters such as distances, colours, masses, radii, and bolometric luminosities. X-ray fluxes and luminosities were determined from observed eROSITA count rates using appropriate rate-to-flux conversion factors. We defined and examined various variability diagnostics in both wavebands and how these parameters are related to each other. Our stars are nearby (mostly within ~100pc ), rotating fast (Prot<9d), and display a high optical flare frequency, as expected from the selection of particularly X-ray-active objects. The optical duty cycle - defined as the fraction of observing time in which the stars were in a high activity state - is well correlated with the optical flare rate and was therefore used as proxy for optical variability. The X-ray and optical duty cycles are positively correlated, and there is a trend of faster rotators tending to have higher X-ray and optical variability. For stars with many X-ray flaring events, the chances of these events being found together with optical flares are high. A quantitative variability study of individual flares in the X-ray light curves is severely affected by data gaps due to the low (4h) cadence during the eROSITA all-sky survey. To mitigate this, we made use of the optical flares observed with TESS combined with knowledge accumulated from solar flares to put additional constraints on the peak flux and timing of X-ray events. With this method we could perform an exponential fit to 17 X-ray light curves in the aftermath of an optical flare, and we find that the energies for these X-ray flares are well correlated with the corresponding optical flare energy. We also found two peculiar flaring events with uncharacteristically long duration and high energies observed in both their X-ray and optical light curves. Despite the substantial uncertainties associated with our analysis, which are mostly related to the poor sampling of the eROSITA light curves, our results showcase in an exemplary way the relevance of simultaneous all-sky surveys in different wavebands for obtaining unprecedented quantitative information on stellar variability.2024A&A...688A..49Jhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A49CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/345 : Gaia DR2 (Gaia Collaboration, 2018)IV/38 : TESS Input Catalog - v8.0 (TIC-8) (Stassun+, 2019)II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/688/A49https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/688/A49http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/688/A49https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/688/A49https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/688/A49http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/688/A49GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/688/A49/tableb1 (Stellar parameters from eRASS)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/688/A49/tableb1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/688/A49/tableb1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/688/A49/tableb1?GETtext/xml+votable180.050000true65.6916730616703-75.12802479334890.0055555555555555566/32886 33030 33037 33060 33088 33094 33222 33237 33239 33850 37035 37382 37402 37442 37482 37566 37569 38932 38948 38950 39049 39054 39056-390571.1166583743361574e-19 3.916500758235022e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/688/A49?format=asciiX-rayOpticalInfrareddefaultJ/A+A/688/A49/tablea1Stellar parameters from Gaia, 2MASS, and TESSrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTICTESS Input Catalogue Identifier (TIC_ID)meta.idcharGaiaDR2Gaia ID from data release 2 (GaiaDR2)meta.id;meta.main2MASS2MASS ID (2MASS)meta.idintDistDistance to the star from Gaia parallax (Distance)pcpos.distancedoublepmRAGaia proper motion right ascension direction (PMRA)mas/yrpos.pm;pos.eq.radoublepmDEGaia proper motion declination direction (PMDEC)mas/yrpos.pm;pos.eq.decdoubleBPmagMagnitude in Gaia BP band (GaiaBP)magphot.mag;em.opt.BdoubleRPmagMagnitude in Gaia RP band (GaiaRP)magphot.mag;em.opt.RdoubleGmagMagnitude in Gaia G band. (GaiaG)magphot.mag;em.optdoubleVmagJohnson-Kron-Cousin V from Gaia magnitudes GBP and GRP (V)magphot.mag;em.opt.VdoubleJmagMagnitude in 2MASS J band (J)magphot.mag;em.IR.JfloatHmagMagnitude in 2MASS H band (H)magphot.mag;em.IR.HfloatKsmagMagnitude in 2MASS K s band (K_s)magphot.mag;em.IR.KfloatRadStellar radius based on radius empirical relations from (Mann et al., 2015ApJ...804...64M) using MKs (Radius)solRadphys.size.radiusdoubleMassStellar mass based on mass empirical relations from (Mann et al., 2015ApJ...804...64M) using MKs (Mass)solMassphys.massdoubleTeffvjjhStellar effective temperatures based on empirical relations from (Mann et al., 2015ApJ...804...64M) using J, H and V (Teff_v_j_j_h)Kphys.temperaturedoubleTeffbprpjhStellar effective temperatures based on empirical relations from (Mann et al., 2015ApJ...804...64M) using BP,RP,J & H (Teff_bp_rp_j_h)Kphys.temperaturedoubleLbolBolometric luminosities calculated from Bolometric corrections to Gaia magnitudes (L_Bol)1e-07Wphys.luminositydoubleTS27Boolean value to indicate whether the star was observed in TESS sector 27 (TESS_sector_27)meta.codeintTS28Boolean value to indicate whether the star was observed in TESS sector 28 (TESS_sector_28)meta.codeintTS29Boolean value to indicate whether the star was observed in TESS sector 29 (TESS_sector_29)meta.codeintTS30Boolean value to indicate whether the star was observed in TESS sector 30 (TESS_sector_30)meta.codeintTS31Boolean value to indicate whether the star was observed in TESS sector 31 (TESS_sector_31)meta.codeintTS32Boolean value to indicate whether the star was observed in TESS sector 32 (TESS_sector_32)meta.codeintTS33Boolean value to indicate whether the star was observed in TESS sector 33 (TESS_sector_33)meta.codeintTS34Boolean value to indicate whether the star was observed in TESS sector 34 (TESS_sector_34)meta.codeintTS35Boolean value to indicate whether the star was observed in TESS sector 35 (TESS_sector_35)meta.codeintTS36Boolean value to indicate whether the star was observed in TESS sector 36 (TESS_sector_36)meta.codeintTS37Boolean value to indicate whether the star was observed in TESS sector 37 (TESS_sector_37)meta.codeintTS38Boolean value to indicate whether the star was observed in TESS sector 38 (TESS_sector_38)meta.codeintTS39Boolean value to indicate whether the star was observed in TESS sector 39 (TESS_sector_39)meta.codeintJ/A+A/688/A49/tableb1Stellar parameters from eRASSrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDR2Gaia ID from data release 2 (GaiaDR2)meta.id;meta.mainRA2Proper motion corrected X-ray right ascension during eRASS 2 (J2000) (RA_CORR_eRASS2)degpos.eq.ra;meta.mainRA3degProper motion corrected X-ray right ascension during eRASS 3 (J2000) (RA_CORR_eRASS3)degpos.eq.raDE2Proper motion corrected X-ray declination during eRASS 2 (J2000) (DEC_CORR_eRASS2)degpos.eq.dec;meta.mainDE3degProper motion corrected X-ray declination during eRASS 3 (J2000) (DEC_CORR_eRASS3)degpos.eq.decSep2Separation along a great circle between the proper motion corrected Gaia-DR2 coordinates and the matched eRASS coordinates RA CORR eRASS2 and DEC CORR eRASS2 (Separation_eRASS2)arcsecpos.angDistancedoubleSep3Separation along a great circle between the proper motion corrected Gaia-DR2 coordinates and the matched eRASS coordinates RA CORR eRASS3 and DEC CORR eRASS3 (separation_eRASS3)arcsecpos.angDistancedoubleDetLike2Detection likelihood in energy band 0.2-5 KeV during eRASS2 (DET_LIKE_eRASS2)stat.likelihooddoubleDetLike3Detection likelihood in energy band 0.2-5 KeV during eRASS2 (DET_LIKE_eRASS3)stat.likelihooddoubleMLrate02Count rate in energy band 0.2-5 KeV during eRASS2 (ML_RATE_0_eRASS2)ct/sphot.count;em.X-raydoubleMLrate03Count rate in energy band 0.2-5 KeV during eRASS2 (ML_RATE_0_eRASS3)phot.count;em.X-raydoubleLxX-ray luminosity from the average ML_RATE_0 from eRASS 2 and eRASS 3 and Gaia distances (L_x)1e-07Wphys.luminosity;em.X-raydoubleFxsurfX-ray surface flux from the average ML_RATE_0 from eRASS 2 and eRASS3 (F_x_surf)mW.m**-2phot.flux;em.X-raydouble