J/A+A/661/A44ivo://CDS.VizieR/J/A+A/661/A44doi:10.26093/cds/vizier.36610044CDSStelzer B.Klutsch A.Coffaro M.Magaudda E.Salvato M.2024-07-15T20:01:27Z2022-05-18T14:01:26ZCDS support team

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

cds-question@unistra.frx-ray-sourcesstellar-flareslate-type-starsWe present the first X-ray detections of ultracool dwarfs (UCDs) from the first all-sky survey of the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) onboard the Russian-German Spektrum-Roentgen-Gamma mission, SRG. We use three publicly available input catalogs of spectroscopically confirmed UCDs and Gaia-selected UCD candidates that together comprise nearly 20000 objects. In a careful source identification procedure we first extract all X-ray sources from the catalog of the first survey, eRASS1, that have an UCD or candidate within three times their positional uncertainty. Then we examine all Gaia objects in the vicinity of these 96 X-ray sources. We associate the most plausible counterpart on the basis of their spatial separation to the X-ray position and their multi-wavelength properties. This way we find 40 UCDs that have a secure identification with an X-ray source (i.e. bona-fide UCD X-ray emitters) and 18 plausible UCD X-ray emitters for which we consider it likely that the X-ray source has its origin in the UCD. Twentyone of the bona-fide and plausible X-ray emitting UCDs have a spectroscopic confirmation, while the others have been selected based on Gaia photometry and we compute spectral types from the G-J color. The spectral types of the X-ray emitting UCDs and candidates range between M5 and M9. The distances of the eRASS1 UCDs range from 3.5 to 190 pc. The spectroscopically confirmed UCDs at the high end of the distance distribution are known to be members of nearby star forming regions. The majority of the UCDs from the eRASS1 sample show a ratio of X-ray to bolometric luminosity well above the canonical saturation limit of log(Lx/Lbol)~-3. For the two most extreme outliers we have verified the hypothesis that these high values are due to flaring activity through an analysis of the eRASS1 lightcurve. X-ray spectra could be analysed for the two brightest objects in terms of count rate, showing both an emission-measure weighted plasma temperature of <kT>=0.75keV. These observations demonstrate the potential of eROSITA for advancing our knowledge on the faint coronal X-ray emission from UCDs by building statistical samples for which the average X-ray brightness, flares and coronal temperatures can be derived.2022A&A...661A..44Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/661/A44CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/345 : Gaia DR2 (Gaia Collaboration, 2018)I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+ 2018)II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+, 2003)II/328 : AllWISE Data Release (Cutri+, 2013)J/A+A/619/L8 : New ultra-cool and brown dwarf candidates in Gaia DR2J/A+A/661/A1 : The eFEDS X-ray catalogs (V7.4) (Brunner+, 2022)J/A+A/661/A2 : Galaxy clusters and groups in eFEDS (Liu+, 2022)J/A+A/661/A3 : eFEDS counterparts to point-like sources (Salvato+, 2022)J/A+A/661/A4 : eFEDS optical cluster and group catalog (Klein+, 2022)J/A+A/661/A5 : The eFEDS AGN catalog (Liu+, 2022)J/A+A/661/A7 : X-ray properties of eFEDS clusters and groups (Bahar+, 2022)J/A+A/661/A8 : eFEDS catalogue of variable X-ray sources (Boller+, 2022)J/A+A/661/A10 : eFEDS galaxy clusters and groups in disguise (Bulbul+, 2022)J/A+A/661/A23 : Exoplanet X-ray irradiation & evaporation rates (Foster+, 2022)J/A+A/661/A24 : Corona-chromosphere connection (Fuhrmeister+, 2022)J/A+A/661/A29 : First eROSITA study of nearby M dwarfs (Magaudda+, 2022)J/A+A/661/A34 : eta Cha cluster eROSITA X-ray scan (Robrade+, 2022)J/A+A/661/A35 : eROSITA study of 47 Tuc globular cluster (Saeedi+, 2022)J/A+A/661/A38 : SRG/ART-XC 1st year all-sky X-ray survey (Pavlinsky+, 2022)J/A+A/661/A44 : A first eROSITA view of ultracool dwarfs (Stelzer+, 2022)https://jgagneastro.com/list-of-m6-m9-dwarfs : The online database ofhttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/661/A44https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/661/A44http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/661/A44https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/661/A44https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/661/A44http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/661/A44GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/661/A44/table1 (Basic X-ray parameters from the eRASS1 catalog for our the UCDs and UCD candidates)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/661/A44/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/661/A44/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/661/A44/table1?GETtext/xml+votable180.050000true34.8420699078792-39.42325762781390.0055555555555555566/4639 4685 4739 4941 5000 5117 6458 6466 20519 21094 21311-21312 21745 22482 22603 22739 24175 24343 25136 26464 26677 26837 27214 27537 27672 27728 32920 33271 33352 33462 33488 33882 33894 33924 33970 34043 34249 34404 34511 34598 34867 35076 35157 35268 35533 35624 35662 35926 36129 36300 36938 36957 37138 37401 37428 37480 37528 37552 37780 38048 38054 38118 38283 38452 38723 38850 38933 39371 39961 40271 40297 40941 41028 41143 41216 41287 41484 41602 41771 41958 42528 42569 43070 43120 43191 43294 44226 44306 44370 44518 45055 45119 45257 45578 473881.5062136169708525e-19 3.916500758235022e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/661/A44?format=asciiX-raydefaultJ/A+A/661/A44/table1Basic X-ray parameters from the eRASS1 catalog for our the UCDs and UCD candidatesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDR2Gaia DR2 (Cat. I/345) designation (source_id)meta.id;meta.mainRAJ2000Right ascension of the boresight corrected eRASS1 positions (J2000) (ra_corr)degpos.eq.ra;meta.mainDEJ2000Declination of the boresight corrected eRASS1 positions (J2000) (dec_corr)degpos.eq.dec;meta.mainePosError on the eRASS1 positions (delta_radec)arcsecstat.errorfloatSepOXSeparation between the proper motion corrected optical positions and the X-ray positions (sep_ox)arcsecpos.angDistancefloatRateBroad band (0.2-5.0 keV) source count rates (rate)ct/sphot.count;em.X-rayfloatSimbadSimbad column added by the CDSmeta.ref.urlchariCatOriginal input catalog (iCat) (1)meta.bibchare_RateError on the broad band (0.2-5.0keV) source count rates (err_rate)ct/sstat.errorfloatDetMLMaximum likelihood for the X-ray detection in the broad band (col. DET_LIKE_0 from eRASS1cat) (detml)stat.likelihoodfloatfuniqucdFlag for UCDs being the unique Gaia counterparts to the eRASS1 source (flag_uniq_ucd)meta.codecharfcpmFlag for common proper motion pairs involving an UCD or UCD candidate (flag_cpm)meta.codecharfxdataFlag for objects with archival X-ray detections (flag_xdata)meta.codecharfbfucdFlag for UCDs considered as 'bona-fide' counterparts to the eRASS1 sources (flag_bona_fide_ucd)meta.codecharfplucdFlag for UCDs considered as 'plausible' counterparts to the eRASS1 sources (flag_plausible_ucd)meta.codecharJ/A+A/661/A44/table2Multi-wavelength properties of the UCDs and UCD candidates identified as bona-fide or plausible counterparts to an eRASS1 X-ray sourcelogLX/Lbollog of the ratio between the eROSITA LX and Lbol from Filippazzo et al. (2015ApJ...810..158F) (LogLxLbol)phys.luminosity;arith.ratiodoublefyoungFlag for young star (flag_young) (4)meta.codecharryoungReference on young star (ref_young)meta.bibcharfbinaryFlag for binary system (flag_binary) (4)meta.codecharrbinaryReference on binary system (ref_binary)meta.bibcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDR2Gaia DR2 (Cat. I/345) designation of the UCD (source_id)meta.id;meta.mainGmagG-band magnitude from the Gaia DR2 catalog (Gmag)magphot.mag;em.optdoubleJmagJ-band magnitude from the 2MASS (Cat. II/246) catalog (Jmag)magphot.mag;em.IR.JfloatW1mag? W1-band magnitude from the AllWISE (Cat. II/328) catalog (W1mag)magphot.mag;em.IR.3-4umfloatnullableSpTypeoptSpectroscopic spectral type in visual bandpass (spt_opt) (1)src.spTypecharSpTypephPhotometric spectral type from the G-J color index (spt_photo) (2)src.spTypecharDistDistance from Bailer-Jones et al. (2018, Cat. I/347) (dist)pcpos.distancedoublee_DistLower error on the distance estimated by Bailer-Jones et al. (2018) (elo_dist)pcstat.errordoubleE_DistUpper error on the distance estimated by Bailer-Jones et al. (2018) (eup_dist)pcstat.error;stat.maxdoublelogLXlog of Lx for the eROSITA band 1+2 (LogLx) (3)log(1e-06W)phys.luminosity;em.X-raydouble