J/ApJ/857/132ivo://CDS.VizieR/J/ApJ/857/132doi:10.26093/cds/vizier.18570132CDSKalari V.M.Carraro G.Evans C.J.Rubio M.2019-05-06T15:33:09Z2019-04-25T11:53:40ZCDS support team

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

cds-question@unistra.fropen-star-clustersmagellanic-cloudsinfrared-photometryvisible-astronomybroad-band-photometryNGC 796 is a massive young cluster located 59kpc from us in the diffuse intergalactic medium of the 1/5-1/10Z_{sun}_ Magellanic Bridge, allowing us to probe variations in star formation and stellar evolution processes as a function of metallicity in a resolved fashion, and providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics griH{alpha} imaging of NGC 796 (at 0.5", which is ~0.14pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore whether star formation and stellar evolution vary as a function of metallicity by comparing the properties of NGC 796 to higher-metallicity clusters. We find an age of 20_-5_^+12^Myr from isochronal fitting of the cluster main sequence in the color-magnitude diagram. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope {alpha}=1.99+/-0.2, hinting at a metallicity and/or environmental dependence of the IMF, which may lead to a top-heavy IMF in the early universe. Study of the H{alpha} emission-line stars reveals that classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990+/-200M_{sun}_, and a core radius of 1.4+/-0.3pc, which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge.2018ApJ...857..132Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/857/132CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/288 : IRSF Magellanic Clouds Point Source Catalog (Kato+ 2007)J/other/Sci/359.69 : Massive stars in 30 Dor (Schneider+, 2018)J/MNRAS/453/1026 : Lagoon Nebula M8 T tauri accretion rates (Kalari+, 2015)J/MNRAS/440/2036 : VPHAS+ survey synthetic colours (Drew+, 2014)J/ApJ/795/108 : Stellar populations in Magellanic bridge (Skowron+, 2014)J/ApJ/785/162 : YSO candidates in the Magellanic Bridge (Chen+, 2014)J/A+A/551/A78 : The Magellanic Bridge Catalog of Stars (Bagheri+, 2013)J/MNRAS/426/2427 : Structural param. of M33 star clusters (San Roman+, 2012)J/AJ/142/48 : LMC star clusters structural parameters (Werchan+, 2011)J/MNRAS/415/103 : IPHAS T Tauri candidates in IC 1396 (Barentsen+, 2011)J/AJ/140/416 : IR photometry of massive stars in the SMC (Bonanos+, 2010)J/A+A/509/A11 : Ha emission-line objects in SMC clusters (Martayan+, 2010)J/ApJ/707/1347 : HST F160W photometry in RMC 136 (Andersen+, 2009)J/MNRAS/382/1203 : CT1 photometry of 5 SMC star clusters (Piatti+, 2007)J/A+A/471/625 : VLT-FLAMES survey of massive stars (Trundle+, 2007)J/ApJ/658/358 : Ae/Be stars of Magellanic Bridge in JHKs (Nishiyama+, 2007)J/ApJ/658/345 : CRIc photometry of Magellanic Bridge Fields (Harris, 2007)J/A+A/430/941 : Star formation region NGC 6530 (Prisinzano+, 2005)J/MNRAS/353/601 : 2dF survey of the Small Magellanic Cloud (Evans+, 2004)J/AJ/114/2644 : UBVRIHa photometry of NGC2264 (Sung+, 1997)J/ApJS/101/41 : SMC and Bridge extended catalog (Bica+ 1995)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/857/132https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/857/132http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/857/132https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/857/132https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/857/132http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/857/132GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/857/132/table2 (4.1m SOAR telescope gri photometry of all stars)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/857/132/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/857/132/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/857/132/table2?GETtext/xml+votable180.050000true29.1022083-74.23902780.0055555555555555566/32956 32957https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/857/132?format=asciiOpticalInfrareddefaultJ/ApJ/857/132/table24.1m SOAR telescope gri photometry of all starsRAJ2000[1] Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000[74] Degree of Declination (J2000)pos.eq.dec;meta.mainrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordint[KCE2018][1/577] Identification numbermeta.id;meta.mainintgmag[13.7/25.4] g band magnitudemagphot.mag;em.opt.Bfloate_gmag[0.02/0.5] Uncertainty in gmagmagstat.error;phot.mag;em.opt.Bfloatrmag[14/24] r band magnitudemagphot.mag;em.opt.Rfloate_rmag[0.02/0.2] Uncertainty in rmagmagstat.error;phot.mag;em.opt.Rfloatimag[14.3/24] i band magnitudemagphot.mag;em.opt.Ifloate_imag[0.04/0.2] Uncertainty in imagmagstat.error;phot.mag;em.opt.IfloatCommAdditional comments (1)meta.notecharK07Display data from Kato+ 2007, II/288 within 0.5"meta.ref.urlintnullableN07Display the data from Nishiyama+, 2007, J/ApJ/658/35meta.ref.urlchar