J/AJ/109/650ivo://CDS.VizieR/J/AJ/109/650doi:10.26093/cds/vizier.51090650CDSBuonanno R.Corsi C.E.Fusi Pecci F.Richer H.B.Fahlman G.G.2023-04-06T16:50:12Z1997-12-09T20:26:29ZCDS support team

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

cds-question@unistra.frglobular-star-clustersccd-photometryWe have obtained the first B,V CCD color-magnitude diagram (CMD) of the galactic globular cluster Arp 2. About 1600 stars have been measured between the tip of the red giant branch at V ~ 15.5 and V ~ 23.5, about two magnitudes below the main sequence turnoff. A centrally concentrated population of blue stragglers has been detected. The slope of the red giant branch and the overall CMD morphology are consistent with that of a metal-poor cluster, with [Fe/H] = 18.4+/-0.25. A preliminary spectroscopic measurement based on the Ca II triplet yields [Fe/H] = -1.73+/-0.05. The comparison of the CMD of Arp 2 with that of other clusters favors a value more metal-poor than that indicated by the Ca II triplet. In this respect, Arp 2 is similar to Ruprecht 106 [Buonanno et al. =1990AJ....100.1811B and =1993AJ....105..184B]. Differential ages between Arp 2 and a number of reference clusters are obtained from the vertical age parameter Delta V^TO_HB, and the horizontal age parameter, {Delta}(B-V)^TO_RGB. By requiring both age estimators to give consistent results, we find that Arp 2 is ~ 3 Gyr younger than the group of the metal-poor clusters and slightly older than Ruprecht 106. The detection of young metal-poor clusters ([Fe/H] <= -1.8) implies a complex scenario for the origin of the galactic halo, possibly involving interactions with satellite galaxies and their cluster systems.1995AJ....109..650Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/109/650CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/109/650https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/109/650http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/109/650https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/109/650https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/109/650http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/109/650GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/AJ/109/650/table2Magnitudes, colors, and positions of stars in the central field of Arp 2recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintStarStar numbermeta.id;meta.mainintVmagV magnitudemagphot.mag;em.opt.VfloatB-V(B-V) colormagphot.color;em.opt.B;em.opt.VfloatXpos*X coordinate in local systemarcsecpos.projintYpos*Y coordinate in local systemarcsecpos.projint