J/A+A/322/460ivo://CDS.VizieR/J/A+A/322/460doi:10.26093/cds/vizier.33220460CDSNordstrom B.Andersen J.Andersen M.I.2008-10-06T11:29:24Z2008-10-06T11:26:06ZCDS support team

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

cds-question@unistra.fropen-star-clustersphotometryradial-velocityBased on new, accurate photometry, radial velocities, and proper motions for the intermediate-age open cluster NGC 3680, we identify individual single and binary cluster members and field stars in the colour-magnitude diagram (CMD). This basic step turns out to be crucial for a proper understanding of the cluster CMD: ~60% of the stars are found to be field stars, and over 50% of the cluster stars are binaries. No bona fide cluster star is found more than 1.5mag below the turnoff, and cluster stars below 1.4M_{sun}_ are only found in binary systems. The total present mass of NGC 3680 is ~100M_{sun}_, excluding any as yet unseen stellar remnants, and its half-mass radius is 3.3' (1.2pc). Comparison with plausible IMFs indicates that only ~3% of the original stars and <~10% of the mass now survive, ~30% of the initial mass being in the form of massive stars that have now completed their evolution, and ~60% in low-mass stars which may now be located in a distant cluster halo or perhaps have been lost entirely. The single main-sequence cluster members form an extremely tight sequence in the CMD, with E_(b-y)_=0.034 and [Fe/H]=+0.11. A direct fit to the Hyades main sequence yields (m-M)_0_=10.5+/-0.2 for NGC 3680. Isochrones from several stellar models have been fit to the cluster sequence. When based on consistent uvby colour transformations and the above cluster parameters, these fits are very stable and show that standard models are not acceptable for stars with the turnoff mass of NGC 3680. Overshooting models perform much better, but further refinement of the overshooting formalism seems to be needed. The age derived for NGC 3680 is 1.45+/-0.3Gyr. The limiting factor in a precise comparison of theory and observations is now the transformation from theoretical to observed parameters, particularly (broad-band) colours.1997A&A...322..460Nhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/322/460CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+AS/118/407 : CCD photometry & velocities of NGC 3680 stars, Paper Ihttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/322/460https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/322/460http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/322/460https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/322/460https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/322/460http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/322/460GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/A+A/322/460/table1Summary data for 120 stars in the field of NGC 3680recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIdIdentification number (see paper)meta.id;meta.maincharVmag? V magnitudemagphot.mag;em.opt.Vfloatnullableb-y? b-y colour indexmagphot.color;em.opt.B;em.opt.Vfloatnullablen_b-y[M] M for missing entrymeta.notecharB-V? B-V colour indexmagphot.color;em.opt.B;em.opt.Vfloatnullablen_B-V[M] M for missing entrymeta.notecharRV? Mean radial velocitykm/sspect.dopplerVeloc;stat.meanfloatnullablen_RV[M] M for missing entrymeta.notechare_RV? Mean error of mean radial velocitykm/sstat.errorfloatnullablen_e_RV[M] M for missing entrymeta.notecharpRV? Radial velocity membership probability (%)meta.code.memberfloatnullablen_pRV[M] M for missing entrymeta.notecharpPM? Proper motion membership probability (%)meta.code.memberintnullablen_pPM[M] M for missing entrymeta.notecharNote1Remarks on binary starsmeta.notecharNote2Remarks on final membership assignmentmeta.code.memberchar