J/A+A/573/A70ivo://CDS.VizieR/J/A+A/573/A70doi:10.26093/cds/vizier.35730070CDSNardiello D.Milone A.P.Piotto G.Marino A.F.Bellini A.,Cassisi S.2015-05-11T10:52:42Z2014-12-19T08:34:34ZCDS support team

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

cds-question@unistra.frglobular-star-clustersinfrared-photometryvisible-astronomyWide-band photometryWe present the photometric analysis of the external regions of three Galactic Globular Clusters: NGC 6121, NGC 6397 and NGC 6752. The main goal is the characterization of the multiple stellar populations along the main sequence (MS) and the study of the radial trend of the different populations hosted by the target clusters. The data have been collected using FORS2 mounted at the ESO/VLT@UT1 telescope in UBVI filters. From these data sets we extracted high-accuracy photometry and constructed color-magnitude diagrams. We exploit appropriate combination of colors and magnitudes which are powerful tools to identify multiple stellar populations, like B versus U-B and V versus c_U,B,I_=(U-B)-(B-I) CMDs. We confirm previous findings of a split MS in NGC 6752 and NGC 6121. Apart from the extreme case of omega Centauri, this is the first detection of multiple MS from ground-based photometry. For NGC 6752 and NGC 6121 we compare the number ratio of the blue MS to the red MS in the cluster outskirts with the fraction of first and second generation stars measured in the central regions. There is no evidence for significant radial trend. The MS of NGC 6397 is consistent with a simple stellar population. We propose that the lack of multiple sequences is due both to observational errors and to the limited sensitivity of U,B,V,I photometry to multiple stellar populations in metal-poor GCs. Finally, we compute the helium abundance for the stellar populations hosted by NGC 6121 and NGC 6752, finding a mild ({Delta}Y~0.02) difference between stars in the two sequences.2015A&A...573A..70Nhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/573/A70CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/490/625 : Abundances of NGC 6121 red giants (Marino+, 2008)J/A+A/425/509 : VI photometry of NGC 6397 (Andreuzzi+, 2004)J/AJ/120/3111 : Stromgren photometry of NGC 6397 (Anthony-Twarog+, 2000)J/AJ/135/2141 : NGC 6397 faint stars F814W+F606W photometry (Richer+, 2008)J/ApJ/709/241 : NGC 6397 X-rays sources Characterisation (Bogdanov+, 2012)J/ApJ/754/91 : Abundances and velocities of NGC 6397 stars (Lovisi+, 2012)J/A+A/557/A128 : Stellar [Fe/H] and [Na/H] in NGC6752 (Carretta, 2013)J/ApJ/750/L14 : Abundances of red giants in NGC 6752 (Carretta+, 2012)J/MNRAS/423/2901 : NGC 6752 multiwavelength survey (Thomson+, 2012)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/573/A70https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/573/A70http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/573/A70https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/573/A70https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/573/A70http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/573/A70GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/573/A70/ngc6397 (NGC 6397 astro-photometric catalog)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/573/A70/ngc6397?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/573/A70/ngc6397?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/573/A70/ngc6397?GETtext/xml+votable180.050000true264.90382-53.663480.005555555555555556Cone search capability for table J/A+A/573/A70/ngc6752 (NGC 6752 astro-photometric catalog)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/573/A70/ngc6752?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/573/A70/ngc6752?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/573/A70/ngc6752?GETtext/xml+votable180.050000true288.02884-60.208678890.005555555555555556Cone search capability for table J/A+A/573/A70/ngc6121 (NGC 6121 astro-photometric catalog)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/573/A70/ngc6121?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/573/A70/ngc6121?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/573/A70/ngc6121?GETtext/xml+votable180.050000true245.763-26.485226110.0055555555555555566/42076 42955 42977 471682.367228618189496e-19 6.118840631666147e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/573/A70?format=asciiOpticalInfrareddefaultJ/A+A/573/A70/ngc6397NGC 6397 astro-photometric catalogIDID number of the star within the clustermeta.id;meta.mainintprimaryRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainXposx master frame positionpixpos.cartesian.x;obs.field;instr.detfloatYposy master frame positionpixpos.cartesian.y;obs.fielddoubleUmagCalibrated U Johnson magnitudemagphot.mag;em.opt.Ufloate_Umagrms error in the U magnitudemagstat.error;phot.mag;em.opt.Ufloatq_UmagQuality of U PSF-fit (1)meta.code.qualfloato_Umag[3/23] Number of images for U magnitudemeta.numberintBmagCalibrated B Johnson magnitudemagphot.mag;em.opt.Bfloate_Bmagrms. error in the B magnitudemagstat.error;phot.mag;em.opt.Bfloatq_BmagQuality of B PSF-fit (1)meta.code.qualfloato_Bmag[3/33] Number of images for B magnitudemeta.numberintVmagCalibrated V Johnson magnitudemagphot.mag;em.opt.Vfloate_Vmagrms. error in the V magnitudemagstat.error;phot.mag;em.opt.Vfloatq_VmagQuality of V PSF-fit (1)meta.code.qualfloato_Vmag[3/46] Number of images for V magnitudemeta.numberintImagCalibrated I Cousins magnitudemagphot.mag;em.opt.Ifloate_Imagrms. error in the I magnitudemagstat.error;phot.mag;em.opt.Ifloatq_ImagQuality of I PSF-fit (1)meta.code.qualfloato_Imag[3/23] Number of images for I magnitudemeta.numberintJ/A+A/573/A70/ngc6752NGC 6752 astro-photometric catalogIDID number of the star within the clustermeta.id;meta.mainintprimaryRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainXposx master frame positionpixpos.cartesian.x;obs.field;instr.detfloatYposy master frame positionpixpos.cartesian.y;obs.fielddoubleUmagCalibrated U Johnson magnitudemagphot.mag;em.opt.Ufloate_Umagrms error in the U magnitudemagstat.error;phot.mag;em.opt.Ufloatq_UmagQuality of U PSF-fit (1)meta.code.qualfloato_Umag[3/23] Number of images for U magnitudemeta.numberintBmagCalibrated B Johnson magnitudemagphot.mag;em.opt.Bfloate_Bmagrms. error in the B magnitudemagstat.error;phot.mag;em.opt.Bfloatq_BmagQuality of B PSF-fit (1)meta.code.qualfloato_Bmag[3/33] Number of images for B magnitudemeta.numberintVmagCalibrated V Johnson magnitudemagphot.mag;em.opt.Vfloate_Vmagrms. error in the V magnitudemagstat.error;phot.mag;em.opt.Vfloatq_VmagQuality of V PSF-fit (1)meta.code.qualfloato_Vmag[3/46] Number of images for V magnitudemeta.numberintImagCalibrated I Cousins magnitudemagphot.mag;em.opt.Ifloate_Imagrms. error in the I magnitudemagstat.error;phot.mag;em.opt.Ifloatq_ImagQuality of I PSF-fit (1)meta.code.qualfloato_Imag[3/23] Number of images for I magnitudemeta.numberintJ/A+A/573/A70/ngc6121NGC 6121 astro-photometric catalogo_Vmag[3/46] Number of images for V magnitudemeta.numberintRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainIDID number of the star within the clustermeta.id;meta.mainintprimaryDEJ2000Declination (J2000)degpos.eq.dec;meta.mainXposx master frame positionpixpos.cartesian.x;obs.field;instr.detfloatYposy master frame positionpixpos.cartesian.y;obs.fielddoubleUmagCalibrated U Johnson magnitudemagphot.mag;em.opt.Ufloate_Umagrms error in the U magnitudemagstat.error;phot.mag;em.opt.Ufloatq_UmagQuality of U PSF-fit (1)meta.code.qualfloato_Umag[3/23] Number of images for U magnitudemeta.numberintBmagCalibrated B Johnson magnitudemagphot.mag;em.opt.Bfloate_Bmagrms. error in the B magnitudemagstat.error;phot.mag;em.opt.Bfloatq_BmagQuality of B PSF-fit (1)meta.code.qualfloato_Bmag[3/33] Number of images for B magnitudemeta.numberintVmagCalibrated V Johnson magnitudemagphot.mag;em.opt.Vfloate_Vmagrms. error in the V magnitudemagstat.error;phot.mag;em.opt.Vfloatq_VmagQuality of V PSF-fit (1)meta.code.qualfloatImagCalibrated I Cousins magnitudemagphot.mag;em.opt.Ifloate_Imagrms. error in the I magnitudemagstat.error;phot.mag;em.opt.Ifloatq_ImagQuality of I PSF-fit (1)meta.code.qualfloato_Imag[3/23] Number of images for I magnitudemeta.numberint