J/A+A/341/163ivo://CDS.VizieR/J/A+A/341/163doi:10.26093/cds/vizier.33410163CDSHearty T.Magnani L.Caillault J.-P.Neuhaeuser R.Schmitt J.H.M.M.,Stauffer J.1999-01-11T16:19:25Z1999-01-11T17:19:01ZCDS support team

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

cds-question@unistra.frx-ray-sourcesThe star formation capability of two molecular clouds at high galactic latitude (|b|>30{deg}) is investigated. Possible pre-main sequence stars in and around the translucent clouds MBM7 and MBM55 have been identified via their X-ray emission by inspecting ROSAT All-Sky Survey observations of the clouds and environs and ROSAT pointed observations of the high-density cores within the clouds. Follow-up optical spectroscopy of the stellar X-ray sources with V<=15.5mag was conducted with the 1.5-m Fred Lawrence Whipple Observatory telescope to identify standard signatures of pre-main sequence stars (LiI {lambda}6708{AA} absorption and H{alpha} emission). We found 11 stars which have lithium equivalent widths, W(Li), above our detection threshold. Three of the stars with lithium also have weak H{alpha} emission. Relative ages for the stars with lithium are estimated by their position on an W(Li) vs. T_eff_ diagram. A calibration derived from data for several clusters with known ages indicates that the stars are older than the translucent high-latitude clouds. This conclusion is supported by a comparison with theoretical evolutionary tracks of the stars from our sample for which we have distance measurements from Hipparcos. We find it is unlikely that any of the X-ray active, lithium-rich stars we identified have formed in the clouds in question. Theoretical and observational arguments support this conclusion and render unlikely the possibility that low-extinction translucent clouds are the sites of star formation.1999A&A...341..163Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/341/163CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1996)IX/11 : ROSAT Source Catalog (Voges+ 1994)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/341/163https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/341/163http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/341/163https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/341/163https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/341/163http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/341/163GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/341/163/table3 (X-ray identified sources with probable stellar optical counterparts)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/341/163/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/341/163/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/341/163/table3?GETtext/xml+votable180.050000true32.84166719.6402780.005555555555555556https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/341/163?format=asciiX-raydefaultJ/A+A/341/163/notesIndividual notesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRXRXJ name of the X-ray sourcemeta.id;meta.maincharm_RX[ac] Multiplicity index on RXJmeta.code.multipcharNoteText of the notemeta.notecharJ/A+A/341/163/table3X-ray identified sources with probable stellar optical counterpartsVmagV magnitudemagphot.mag;em.opt.Vfloatn_Vmag[:b] Uncertainty flag or note (2)meta.notecharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNote[ABCD] Source localisation (1)meta.notecharRXRXJ name of the X-ray sourcemeta.id;meta.maincharprimarym_RX[abcd] Multiplicity index on Namemeta.code.multipcharn_RX[*] *: This source was detected in both the RASS and ROSAT pointed observations.meta.notecharRA2000Right ascension (2000)pos.eq.ra;meta.mainDE2000Declination (2000)pos.eq.dec;meta.mainMLMaximum likelihood of existencestat.likelihoodfloatCountRateBroad band (0.1-2.0 keV) count ratect/sphot.count;em.X-raydoublee_CountRaterms uncertainty on CountRatect/sstat.errordoublel_HR1limit flag on HR1meta.code.errorcharHR1Hardness ratio 1phot.flux;arith.ratiofloate_HR1? rms uncertainty on HR1stat.errorfloatnullablel_HR2Limit flag on HR2meta.code.errorcharHR2? Hardness ratio 2phot.flux;arith.ratiofloatnullablee_HR2? rms uncertainty on HR2stat.errorfloatnullablelog(fx/fv)X-ray to optical flux ratiophot.flux;arith.ratiofloatSpTypeSpectral type of the optical counterpartsrc.spTypecharEWHa? H{alpha} equivalent width (3)0.1nmspect.line.eqWidthfloatnullablen_EWHa[-] When intervalmeta.notecharEWHa2? Second H{alpha} equivalent width value when interval0.1nmspect.line.eqWidthfloatnullableEWLi? Li (6708{AA}) equivalent width (3)spect.line.eqWidthfloatnullableComComment (4)meta.notechar