J/ApJ/770/98ivo://CDS.VizieR/J/ApJ/770/98doi:10.26093/cds/vizier.17700098CDSvan den Berg M.Verbunt F.Tagliaferri G.Belloni T.Bedin L.R.,Platais I.2015-02-25T17:43:24Z2015-02-03T12:20:38ZCDS support team

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

cds-question@unistra.fropen-star-clustersx-ray-binary-starsastronomical-object-identificationinfrared-photometryvisible-astronomybroad-band-photometryvariable-starsWe present the first X-ray study of NGC 6791, one of the oldest open clusters known (8Gyr). Our Chandra observation is aimed at uncovering the population of close interacting binaries down to L_X_~1x10^30^erg/s (0.3-7keV). We detect 86 sources within 8' of the cluster center, including 59 inside the half-mass radius. We identify 20 sources with proper-motion cluster members, which are a mix of cataclysmic variables (CVs), active binaries (ABs), and binaries containing sub-subgiants. With follow-up optical spectroscopy, we confirm the nature of one CV. We discover one new, X-ray variable candidate CV with Balmer and He II emission lines in its optical spectrum; this is the first X-ray-selected CV in an open cluster. The number of CVs per unit mass is consistent with the field, suggesting that the 3-4 CVs observed in NGC 6791 are primordial. We compare the X-ray properties of NGC 6791 with those of a few old open (NGC 6819, M67) and globular clusters (47 Tuc, NGC 6397). It is puzzling that the number of ABs brighter than 1x10^30^erg/s normalized by cluster mass is lower in NGC 6791 than in M 67 by a factor ~3-7. CVs, ABs, and sub-subgiants brighter than 1x10^30^erg/s are under-represented per unit mass in the globular clusters compared to the oldest open clusters, and this accounts for the lower total X-ray luminosity per unit mass of the former. This indicates that the net effect of dynamical encounters may be the destruction of even some of the hardest (i.e., X-ray-emitting) binaries.2013ApJ...770...98Vhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/770/98CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/chandra : The Chandra Archive Log (CXC, 1999-2014)B/cb : Cataclysmic Binaries, LMXBs, and related objects (Ritter+, 2014)B/hst : HST Archived Exposures Catalog (STScI, 2007)IX/15 : Einstein EMSS Survey (Gioia+ 1990, Stocke+ 1991)J/AJ/148/61 : WIYN open cluster. LIX. NGC 6791 RVs (Tofflemire+, 2014)J/AJ/147/4 : HST photometry of 5 globular clusters (Ross+, 2014)J/A+A/548/A97 : Catalogue of variable stars in open clusters (Zejda+, 2012)J/A+A/543/A106 : UBVRI photometry in NGC6791 (Brogaard+, 2012)J/ApJ/758/110 : CN and CH indexes in stars of NGC 6791 (Carrera, 2012)J/A+A/525/A2 : Eclipsing binaries in NGC6791 (Brogaard+, 2011)J/ApJ/729/L10 : KIC stars properties in NGC 6791 and NGC 6819 (Basu+, 2011)J/A+A/493/339 : XMM-Newton serendipitous Survey. V. (Watson+, 2009)J/A+A/484/609 : BVI photometry and proper motions in M67 (Yadav+, 2008)J/AJ/136/2107 : Distances of cataclysmic variables (Thorstensen+, 2008)J/A+A/471/515 : V light curves of NGC 6791 variable stars (De Marchi+, 2007)J/AJ/133/1585 : Stromgren photometry in NGC 6791 (Anthony-Twarog+, 2007)J/AJ/129/2856 : Variable stars in NGC 6791 (Mochejska+, 2005)J/AJ/129/656 : Infrared photometry of NGC 6791 (Carney+, 2005)J/A+A/418/509 : Chandra observation of M67 (Van Den Berg+, 2004)J/PASP/115/413 : BVI photometry in the open cluster NGC 6791 (Stetson+, 2003)J/AJ/126/3017 : Distances of Cataclysmic variables (Thorstensen, 2003)J/AJ/123/3460 : Low-amplitude variables in NGC 6791 (Mochejska+, 2002)J/A+A/333/231 : O-M stars model atmospheres (Bessell+ 1998)J/ApJ/469/355 : Teff, B-V and BC relation (Flower, 1996)J/A+AS/114/1 : CCD UBVI photometry of NGC 6791 (Kaluzny+, 1995)J/AJ/108/585 : UBVI photometry of NGC 6791 (Montgomery+, 1994)J/MNRAS/243/492 : BV Photometry of NGC 6791 (Kaluzny, 1990)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/770/98https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/770/98http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/770/98https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/770/98https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/770/98http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/770/98GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/770/98/table1 (Chandra sources within 8' of the center of NGC 6791)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/770/98/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/770/98/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/770/98/table1?GETtext/xml+votable180.050000true290.18717537.777870.0055555555555555566/14573 145753.322582951404819e-19 3.852589004194616e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/770/98?format=asciiOpticalInfrareddefaultJ/ApJ/770/98/table1Chandra sources within 8' of the center of NGC 6791ODisplay the optical counterpart properties (table 2)meta.ref.urlcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintLocInside/Outside source location (1)meta.notecharSeq[1/86] Source number (2)meta.idintprimaryf_Seq[*] Limit of detection (3)meta.codecharCXOUSource name (HHMMSS.s+DDMMSS; J2000)meta.id;meta.maincharRAJ2000Right Ascension; decimal degrees (J2000) (4)degpos.eq.ra;meta.mainDEJ2000Declination; decimal degrees (J2000) (4)degpos.eq.dec;meta.mainr95[0.3/4] The 95% positional uncertainty radiusarcsecstat.errorfloatOffset[0.3/8] Angular offset from cluster centerarcminpos.angDistance;arith.difffloatCts[3/213] Net 0.3-7 keV band countsctphot.count;em.X-rayinte_CtsUncertainty in Ctsctstat.errorintf_Cts[bc] Unreliable flux (5)meta.codecharFX[4/318] Unabsorbed 0.3-7keV flux (6)1e-19W.m**-2phot.flux;em.X-rayfloatE50[0.8/3.3]? Median 0.3-7keV band energy (7)keVem.energyfloatnullablee_E50? Uncertainty in E50keVstat.errorfloatnullableJ/ApJ/770/98/table2Optical properties of candidate counterpartsu_B-VB-V uncertainty flagmeta.code.error;phot.color;em.opt.BcharMmGroup membership (1)meta.code.membercharV-I? V-I color index (6)magphot.color;em.opt.V;em.opt.IfloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/86] Source number (as in table 1)meta.id;meta.mainintf_Seqa: this source has another candidate counterpart (see table 3) (2)meta.codecharOID[553/15561]? Number of candidate optical counterpart in the S03 catalog (3)meta.id.crossintnullabledOX[0/3] Angular separation between the X-ray and optical source after correcting for boresightarcsecpos.angDistancefloatpmu[0/99]? Probability for cluster membership (4)stat.fit.goodnessintnullablepMembership probability from HST/ACS (5)meta.code.membercharVmag[11.5/28.5]? V-band magnitude (6)magphot.mag;em.opt.Vfloatnullablef_Vmag[:b] Uncertain or previoulsy unknown (7)meta.codecharB-V? B-V color index (6)magphot.color;em.opt.B;em.opt.Vfloatnullableu_V-IUncertainty flag on V-Imeta.code.error;phot.color;em.opt.VcharLX[1/53]? Unabsorbed X-ray (0.3-7keV) luminosity (8)log(1e-07W)phys.luminosity;em.X-rayfloatnullablel_FX/FVLimit flag on FX/FVmeta.code.error;phys.abundcharFX/FV[-5.1/2.1] Ratio of X-ray (0.3-7keV) to V band fluxes after correcting for extinctionphot.flux;arith.ratiofloatu_FX/FVUncertainty flag on FX/FVmeta.code.error;phys.abundchare_FX/FV[0.03/0.3]? FX/FV uncertaintystat.error;phys.abundfloatnullableVarName of the associated optical variablemeta.idcharPer[0.2/50.5]? Period of variabilitydtime.periodfloatnullablen_Per[s] another period value is 23.947meta.notecharOptSpectroscopic properties of the candidate optical counterpartmeta.notecharClassSource class (9)src.classcharCommComments (10)meta.notechar