J/MNRAS/356/1583ivo://CDS.VizieR/J/MNRAS/356/1583doi:10.26093/cds/vizier.73561583CDSBurningham B.Naylor T.Littlefair S.P.Jeffries R.D.2024-06-30T20:16:58Z2008-08-26T12:41:37ZCDS support team

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

cds-question@unistra.fropen-star-clusterspre-main-sequence-starsdwarf-starsradial-velocityline-intensitiesWe present radial velocities for 38 low-mass candidate members of the {sigma} Orionis young group. We have measured their radial velocities by cross-correlation of high-resolution (R>>6000) AF2/Wide Field Fibre Optical Spectrograph (WYFFOS) spectra of the gravity-sensitive NaI doublet at 8183,8195{AA}, on the nights of 2003 January 3 and 4. The total sample contained 117 objects, of which 54 have sufficient signal-to-noise ratio to detect NaI at an equivalent width of 3{AA}; however, we only detect NaI in 38 of these. This implies that very low-mass members of this young group display weaker NaI absorption than similarly aged objects in the Upper Scorpius OB association. We develop a technique to assess membership using radial velocities with a range of uncertainties that does not bias the selection when large uncertainties are present. The resulting membership probabilities are used to assess the issue of exclusion in photometric selections, and we find that very few members are likely to be excluded by such techniques. We also assess the level of contamination in the expected pre-main-sequence region of colour-magnitude space brighter than I=17. We find that contamination by non-members in the expected pre-main-sequence region of the colour-magnitude diagram is small. We conclude that although radial velocity alone is insufficient to confirm membership, high signal-to-noise ratio observations of the NaI doublet provide the opportunity to use the strength of NaI absorption in concert with radial velocities to asses membership down to the lowest masses, where lithium absorption no longer distinguishes youth.2005MNRAS.356.1583Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/356/1583CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/MNRAS/356/89 : sigma Ori low-mass stars (Kenyon+, 2005)J/AJ/128/2316 : BVRIJHKs photometry in sigma Ori cluster (Sherry+, 2004)J/A+A/419/249 : RJHKs phot. of sigma Ori low-mass stars (Scholz+, 2004)J/AN/325/705 : RIJHKs of low-mass stars in sigma Ori (Bejar+, 2004)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/356/1583https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/356/1583http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/356/1583https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/356/1583https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/356/1583http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/356/1583GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/MNRAS/356/1583/table3 (Equivalent widths and radial velocities measured using the NaI doublet.)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/MNRAS/356/1583/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/MNRAS/356/1583/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/MNRAS/356/1583/table3?GETtext/xml+votable180.050000true84.95379583-2.486402780.0055555555555555566/22851 22854https://cdsarc.cds.unistra.fr/viz-bin/moc/J/MNRAS/356/1583?format=asciiOpticaldefaultJ/MNRAS/356/1583/table3Equivalent widths and radial velocities measured using the NaI doublet.recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFieldField number (1)meta.id;obs.fieldfloatStarObject number (1)meta.idintRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainIcmagCousins I magnitudemagphot.mag;em.opt.Ifloate_Icmagrms uncertainty on Imagmagstat.error;phot.mag;em.opt.Ifloatq_IcmagQuality flag in Icmag (2)meta.code.qualcharRc-IcCousins R-I colour index0.1nmphot.color;em.opt.R;em.opt.Ifloate_Rc-Icrms uncertainty on Rc-Ic0.1nmstat.error;phot.color;em.opt.Rfloatq_Rc-IcQuality flag in Rc-Ic (2)meta.code.qual;phot.color;em.opt.RcharEWEquivalent width of NaI doublet (8183/8195{AA}) integrated over the range 8180-8202{AA} (3)km/sspect.line.eqWidthfloate_EWrms uncertainty on EWkm/sstat.error;spect.line.eqWidthfloatRVbar? Barycentric radial velocity (4)km/sspect.dopplerVeloc;pos.heliocentricfloatnullablef_RVbar[X] X=cross-correlation failedmeta.codechare_RVbar? rms uncertainty on RVbar%stat.errorfloatnullablePvel? Membership probability from velocity measurements%statfloatnullableKJN05Details from the photometric catalogue by Kenyon, Jeffries, Naylor et al. 2005, available in Cat. J/MNRAS/356/89meta.ref.urlchar