J/A+A/402/571ivo://CDS.VizieR/J/A+A/402/571doi:10.26093/cds/vizier.34020571CDSHuensch M.Weidner C.Schmitt J.H.M.M.2003-10-29T18:43:13Z2003-10-29T19:42:25ZCDS support team

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

cds-question@unistra.fropen-star-clustersx-ray-sourcesWe have conducted a detailed study of the object NGC 2451, which actually consists of two different open clusters A and B along the same line of sight at 206pc and 370pc distance, respectively. Although belonging to the nearest clusters, they have not been much investigated until present due to strong contamination by field stars. ROSAT X-ray observations and optical UBVR photometry are used to identify cluster members by means of X-ray emission and colour-magnitude diagrams. The identified stars concentrate nicely around the expected main sequences in the colour-magnitude diagram at the distances derived from astrometric investigations. Altogether, 39 stars are identified as member candidates of the nearer cluster A, 49 stars as member candidates of the more distant cluster B, and 22 faint stars are probably members of either of the two clusters, but due to large errors it is not clear to which one they belong. Further 40 stars identified with X-ray sources are probably non-members. For the first time, the range of known probable cluster members of NGC 2451 A and B has been extended downwards the main sequence to stars of spectral class M. Isochrone fitting yields an age of 50 to 80Myrs for NGC 2451 A and =~50Myrs for NGC 2451 B, consistent with the X-ray luminosity distribution functions, which are comparable to other clusters in the same age range. Except from the occurence of four flares, the stars of both clusters do not show strong long-term X-ray variability exceeding a factor 5 over a time span of 1 to 3 years.2003A&A...402..571Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/402/571CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/341/469 : Geneva photometry of NGC 2451 and HR 2968 (Carrier+ 1999)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/402/571https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/402/571http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/402/571https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/402/571https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/402/571http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/402/571GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/402/571/sources (Final list of X-ray sources identified with stars (tables 7-10 of paper))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/402/571/sources?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/402/571/sources?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/402/571/sources?GETtext/xml+votable180.050000true116.5375-37.41250.0055555555555555566/39353-39355 39696-39697https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/402/571?format=asciiX-raydefaultJ/A+A/402/571/x-obsDetected X-ray sources (tables 3-6 of paper)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObs[ABCH] Detection location (1)meta.code;instrcharprimaryXnoX-ray source numbermeta.id;meta.mainintprimaryCRX-ray count ratect/sphot.count;em.X-raydoublee_CRMean error on CRct/sstat.errordoubleHR? Hardness ratiophot.flux;arith.ratiofloatnullableXfluxX-ray flux (in 10^-13^erg/cm^2^/s)1e-16W.m**-2phot.flux;em.X-rayfloatXlum? X-ray luminosity (2)1e+23Wphys.luminosity;em.X-rayfloatnullableeDet[h s UV] source is detected in the soft (s), hard (h) passband only, and also in UVmeta.codecharJ/A+A/402/571/sourcesFinal list of X-ray sources identified with stars (tables 7-10 of paper)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMem[ABnm] Member of NGC 2451A (A) or NGC 2451B (B), m=member n=non-membermeta.code.membercharXnoX-ray source numbermeta.id;meta.mainintWno? Williams numbermeta.id.crossintnullablem_WnoMultiplicity index on Wnometa.code.multipcharRAJ2000Right Ascension J2000 (hours)pos.eq.ra;meta.mainDEJ2000Declination J2000 (degrees)pos.eq.dec;meta.mainOffOffset between X-ray and optical positionsarcsecpos.angDistanceintVmagV magnitudemagphot.mag;em.opt.Vfloatf_Vmag[*] *: value from the literature (2)meta.code.errorcharB-VB-V color indexmagphot.color;em.opt.B;em.opt.Vfloatf_B-V[*] *: value from the literature (2)meta.code.errorchar(B-V)0De-reddened color indexmagphot.color;em.opt.B;em.opt.VfloatVar[X] X: significant variations in the X-ray fluxmeta.code;src.varcharlog(LX)? X-ray luminositylog(1e+23W)phys.luminosity;em.X-rayfloatnullablelog(LX/Lbol)? Fraction of luminosity in X-rayphys.luminosity;arith.ratiofloatnullableSpSpectral type, in parentheses when derived from color indexsrc.spTypecharOptIDOptical identificationmeta.id.crosscharn_Xno[*] indicates a note detailed in notes.datmeta.notecharJ/A+A/402/571/notesIndividual notesXnoX-ray source numberphot.count;em.X-rayintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObsDetection location, as in file x-obs.datmeta.code;instrcharNotetext of the notemeta.notechar