J/ApJ/920/99ivo://CDS.VizieR/J/ApJ/920/99doi:10.26093/cds/vizier.19200099CDSSuarez G.,Metchev S.,Leggett S.K.,Saumon D.,Marley M.S.2023-08-25T13:13:30Z2023-05-12T09:31:58ZCDS support team

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

cds-question@unistra.frbrown-dwarfsinfrared-astronomyspectroscopyWe present Spitzer IRS 5-14{mu}m spectra and 16{mu}m and 22{mu}m photometry of the T2.5 companion to the ~300Myr old G0V star HN Peg. We incorporate previous 0.8-5{mu}m observations to obtain the most comprehensive spectral energy distribution (SED) of an intermediate-gravity L/T-transition dwarf that, together with an accurate Gaia EDR3 parallax of the primary, enables us to derive precise fundamental parameters. We find that young (~0.1-0.3Gyr) early-T dwarfs on average have ~140K lower effective temperatures, ~20% larger radii, and similar bolometric luminosities compared to >~1Gyr old field dwarfs with similar spectral types. Our accurate infrared spectrophotometry offers new detail at wavelengths where the dominant carbon-bearing molecules have their strongest transitions: at 3.4{mu}m for methane and at 4.6{mu}m for carbon monoxide. We assess the performance of various widely available photospheric models and find that models with condensates and/or clouds better reproduce the full SED of this moderately young early-T dwarf. However, cloud-free models incorporating a more general convective instability treatment reproduce at least the low-resolution near-infrared spectrum similarly well. Our analysis of R~2300 J-band spectra shows that the near-infrared potassium absorption lines in HN Peg B have similar strengths to those seen in both younger and older T2-T3 dwarfs. We conclude that while alkali lines are well established as surface gravity indicators for L-type or warmer stars, they are insensitive to surface gravity in early-T dwarfs.2021ApJ...920...99Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/920/99CatalogResearchIsServedByTAP VizieR generic servicerelated-toVII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)J/ApJ/564/421 : Spectra of T dwarfs. I. (Burgasser+, 2002)J/AJ/127/3553 : JHK photometry & spectroscopy for L & T dwarfs (Knapp+, 2004)J/ApJS/159/141 : Spectroscopic properties of cool stars. I. (Valenti+, 2005)J/ApJ/637/1067 : Near-IR spectral classification of T dwarfs (Burgasser+, 2006)J/AJ/134/1162 : 11 new T dwarfs in 2MASS (Looper+, 2007)J/ApJS/173/104 : Stellar population in Chamaeleon I (Luhman, 2007)J/ApJ/689/1295 : Li test implications for brown dwarfs (Kirkpatrick+, 2008)J/ApJ/710/1142 : SpeX spectroscopy of low mass binaries. I. (Burgasser+, 2010)J/ApJS/201/19 : Hawaii Infrared Parallax Program. I. (Dupuy+, 2012)J/ApJ/810/158 : M,L,T dwarfs fundamental parameters & SEDs (Filippazzo+, 2015)J/other/Sci/350.64 : 51 Eri b near-infrared spectrum (Macintosh+, 2015)J/A+A/589/A21 : K-H2 line shapes for cool brown dwarfs spectra (Allard+, 2016)J/ApJS/225/10 : Kinematic analysis of M7-L8 dwarfs (Faherty+, 2016)J/ApJS/231/15 : Astrometric monitoring ultracool dwarf binaries (Dupuy+, 2017)J/ApJ/838/73 : Brown dwarf surface gravity with Keck/NIRSPEC (Martin , 2017)J/AJ/159/257 : Hawaii IR plx program. IV. L0-T8 BDs with UKIRT (Best+, 2020)J/ApJ/891/171 : COCONUTS. I. Spectra of a WD & T4 comoving syst (Zhang+, 2020)J/A+A/648/A73 : Discovery of the directly imaged planet YSES 2b (Bohn+, 2021)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/920/99https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/920/99http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/920/99https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/920/99https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/920/99http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/920/99GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapInfrareddefaultJ/ApJ/920/99/fig10Near- and mid-IR spectra of HN Peg BrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintInstInstrument identifier (1)meta.id;instrcharWave[0.85/14.2] Wavelengthumem.wl;em.IRdoubleFlux[4e-19/2e-16] Observed fluxcW.m**-2.nm**-1em.IRdoublee_Flux[0/5e-17] Uncertainty in fluxcW.m**-2.nm**-1stat.error;phot.fluxfloatJ/ApJ/920/99/table1Summary of observationsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObs.TypeType of observation; photometry or spectroscopymeta.code;obscharInstInstrument usedmeta.id;instrcharBandBand or wavelength observedinstr.bandpassResResolution (for spectroscopy)spect.resolutioncharObsObservation date(s)time.epoch;obsRefReference used (1)meta.refint