J/ApJ/951/139ivo://CDS.VizieR/J/ApJ/951/139CDSDamian B.Jose J.Biller B.Herczeg G.J.Albert L.Allers K.,Zhang Z.Liu M.C.Dubber S.Paul KTChen W.-P.Lalchand B.,Sharma T.Oasa Y.2026-03-02T06:25:50Z2025-09-26T10:57:48ZCDS support team

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

cds-question@unistra.fropen-star-clustersinfrared-photometryinfrared-astronomyspectroscopyyoung-stellar-objectsstellar-spectral-typesstellar-agesstellar-masseseffective-temperatureLow-mass stars and substellar objects are essential in tracing the initial mass function (IMF). We study the nearby young {sigma} Orionis cluster (d~408pc, age~1.8Myr) using deep near-infrared (NIR) photometric data in the J, W, and H bands from WIRCam on the Canada-France-Hawaii Telescope. We use the water absorption feature to select brown dwarfs photometrically and confirm their nature spectroscopically with IRTF-SpeX. Additionally we select candidate low-mass stars for spectroscopy and analyze their membership and those of literature sources using astrometry from Gaia DR3. We obtain NIR spectra for 28 very-low-mass stars and brown dwarfs and estimate their spectral type between M3 and M8.5 (masses ranging between 0.3 and 0.01M_{sun}_). Apart from these, we also identify five new planetary-mass candidates which require further spectroscopic confirmation of youth. We compile a comprehensive catalog of 170 spectroscopically confirmed members in the central region of the cluster, for a wide mass range of ~19-0.004M_{sun}_. We estimate the star-to-brown-dwarf ratio to be ~4, within the range reported for other nearby star-forming regions. With the updated catalog of members we trace the IMF down to 4M_Jup_ and we find that a two-segment power law fits the substellar IMF better than a log-normal distribution.2023ApJ...951..139Dhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/951/139CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)J/A+A/337/403 : Low-mass stars evolutionary models (Baraffe+ 1998)J/AN/325/705 : RIJHKs of low-mass stars in sigma Ori (Bejar+, 2004)J/MNRAS/356/89 : sigma Ori low-mass stars (Kenyon+, 2005)J/ApJS/173/104 : Stellar population in Chamaeleon I (Luhman, 2007)J/AJ/134/411 : Properties of IC 348 members (Muench+, 2007)J/A+A/488/167 : Low-mass stars in {sigma} Ori & {lambda} Ori (Sacco+, 2008)J/ApJS/190/100 : NIR proper motion survey using 2MASS (Kirkpatrick+, 2010)J/ApJ/743/64 : Deep IR photometry of {sigma} Ori cluster (Bejar+, 2011)J/ApJ/748/14 : ONC population data from WFI observations (Da Rio+, 2012)J/ApJ/754/30 : VISTA IR phot. of {sigma} Ori cluster (Pena Ramirez+, 2012)J/A+A/548/A56 : X-shooter sp. of 12 young stellar objects (Rigliaco+, 2012)J/ApJS/208/9 : Intrinsic colors & temperatures of PMS stars (Pecaut+, 2013)J/ApJ/778/96 : Spitzer and NEWFIRM observations of NGC 6334 (Willis+, 2013)J/ApJ/786/97 : Photospheric properties of T Tauri stars (Herczeg+, 2014)J/ApJ/794/36 : {sigma} Orionis cluster stellar pop. (Hernandez+, 2014)J/ApJ/810/158 : M,L,T dwarfs fundamental param. & SEDs (Filippazzo+, 2015)J/AJ/154/256 : VLM stars and BDs in Upper Sco using Gaia DR1 (Cook+, 2017)J/ApJ/836/98 : YSOs search in Stock 8 with opt. to IR photom. (Jose+, 2017)J/AJ/153/46 : Spectroscopy of candidate members in Taurus (Luhman+, 2017)J/ApJ/858/41 : PS1 proper-motion survey for BDs. I. Taurus (Zhang+, 2018)J/A+A/629/A114 : sigma Ori GTC+INT spectroscopy (Caballero+, 2019)J/ApJ/870/32 : Kinematics in young star clusters & assoc. (Kuhn+, 2019)J/MNRAS/486/1718 : System IMF of 25 Ori (Suarez+, 2019)J/A+A/621/A14 : Blind photometric study of NGC 2264 region (Venuti+, 2019)J/AJ/163/64 : Adopted members of Corona Australis (Esplin+, 2022)J/A+A/670/A37 : Spatial & dynamical structure of NGC2264 (Flaccomio+, 2023)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/951/139https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/951/139http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/951/139https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/951/139https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/951/139http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/951/139GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/951/139/catalog (Complete membership catalog of sources in the sigma Orionis cluster (Table 1) and physical parameters (Table 2))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/951/139/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/951/139/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/951/139/catalog?GETtext/xml+votable180.050000true84.6865-2.60.0055555555555555566/22851 228541.1195963761719405e-19 1.6902755605203292e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/951/139?format=asciiInfrareddefaultJ/ApJ/951/139/catalogComplete membership catalog of sources in the sigma Orionis cluster (Table 1) and physical parameters (Table 2)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSet[1/4] Subset of objects (1)meta.noteintIDObject ID, this workmeta.id;meta.maincharf_IDFlag on object (2)meta.codecharRAJ2000[84.5/84.9] Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[-2.8/-2.38] Declination (J2000)degpos.eq.dec;meta.mainJmag[4.75/20.3] CFHT/WIRCAM J band magnitudemagphot.mag;em.IR.Jfloate_Jmag[0.0/0.26] Uncertainty in Jmagmagstat.error;phot.mag;em.IR.JfloatWmag[12.28/20.24]? CFHT/WIRCAM W-band (1.45um) magnitudemagphot.mag;em.IR.Jfloatnullablee_Wmag[0.0/0.13]? Uncertainty in Wmagmagstat.error;phot.mag;em.IR.JfloatnullableHmag[4.64/19.3] CFHT/WIRCAM H band magnitudemagphot.mag;em.IR.Hfloate_Hmag[0.0/0.25] Uncertainty in Hmagmagstat.error;phot.mag;em.IR.HfloatQ[-1.97/0.3]? reddening insensitive Q-index, Equation 1phot.color.reddFreefloatnullablee_Q[0/0.4]? Uncertainty in Qstat.error;phot.color.reddFreefloatnullableSIMBADName taken from SIMBADmeta.idcharSpTSpectral Type(s) (3)src.spTypecharRefReference(s) (4)meta.bibcharDateIRTF/SpeX observation date for 28 sources; column added by CDStime.epoch;obsnullablefitsDownload the FITS file for the 28 observed sourcesmeta.ref.urlcharSimbadSimbad column added by the CDSmeta.ref.urlcharSpT2Spectral Type (5)src.spTypecharTeff[1581/31900]? Surface effective temperature (6)Kphys.temperature.effectiveintnullablelogLs[-3.47/4.72]? Log, bolometric luminosity (6)log(solLum)phys.luminosityfloatnullablel_AgeLimit flag on Agemeta.code.error;time.agecharAge[0.5/100]? Age (6)Myrtime.agefloatnullableMass[0.004/18.7]? Mass (6)solMassphys.massfloatnullable