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J/ApJ/837/130 Collinder 261 Chandra sources & optical counterparts (Vats+, 2017)

A Chandra X-ray census of the interacting binaries in old open clusters - Collinder 261. Vats S., van den Berg M. <Astrophys. J., 837, 130-130 (2017)> =2017ApJ...837..130V (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; X-ray sources ; Photometry, UBV ; Cross identifications ; Binaries, X-ray ; Binaries, cataclysmic Keywords: binaries: close; novae, cataclysmic variables; open clusters and associations: individual: Collinder 261; stars: activity; X-rays: binaries Abstract: We present the first X-ray study of Collinder 261 (Cr261), which at an age of 7Gyr is one of the oldest open clusters known in the Galaxy. Our observation with the Chandra X-Ray Observatory is aimed at uncovering the close interacting binaries in Cr261, and reaches a limiting X-ray luminosity of LX∼4x1029erg/s (0.3-7keV) for stars in the cluster. We detect 107 sources within the cluster half-mass radius rh, and we estimate that among the sources with LX≳1030erg/s, ∼26 are associated with the cluster. We identify a mix of active binaries and candidate active binaries, candidate cataclysmic variables, and stars that have "straggled" from the main locus of Cr261 in the color-magnitude diagram. Based on a deep optical source catalog of the field, we estimate that Cr261 has an approximate mass of 6500M, roughly the same as the old open cluster NGC6791. The X-ray emissivity of Cr261 is similar to that of other old open clusters, supporting the trend that they are more luminous in X-rays per unit mass than old populations of higher (globular clusters) and lower (the local neighborhood) stellar density. This implies that the dynamical destruction of binaries in the densest environments is not solely responsible for the observed differences in X-ray emissivity. Description: Cr 261 was observed with the Advanced CCD Imaging Spectrometer (ACIS) on board Chandra starting 2009 November 9 14:50 UTC, for a total exposure time of 53.8ks (ObsID 11308). We retrieved optical images of Cr 261 in the B and V bands from the ESO public archive. These data were taken as part of the ESO Imaging Survey (EIS; program ID 164.O-0561). The observations of Cr 261 were made using the Wide Field Imager (WFI), mounted on the 2.2m MPG/ESO telescope at La Silla, Chile. The Cr 261 data were taken from 2001 June 27 23:55 UTC to 2001 June 28 00:38 UTC, with a total exposure time of 510s in the B and V filter each. Objects: ---------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------- 12 38 07.1 -68 23 33 Cr 261 = Cl Collinder 261 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 90 151 Catalog of Chandra sources in Cr 261 table2.dat 81 135 Optical Counterpart Properties
See also: B/chandra : The Chandra Archive Log (CXC, 1999-2014) B/eso : ESO Science Archive Catalog (ESO, 1991-2016) I/284 : The USNO-B1.0 Catalog (Monet+ 2003) VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006) I/317 : The PPMXL Catalog (Roeser+ 2010) J/A+A/418/509 : Chandra observation of M67 (Van Den Berg+, 2004) J/ApJ/635/214 : Chandra X-ray sources and NIR identifications (Ebisawa+, 2005) J/A+A/438/291 : X-ray sources in NGC 188 (Gondoin+, 2005) J/A+A/453/635 : Modelling the Galactic Interstellar Extinct. (Marshall+, 2006) J/AJ/135/2264 : Stellar radial velocities in NGC 188 (Geller+, 2008) J/A+A/490/113 : X-ray sources in NGC 752 (Giardino+, 2008) J/MNRAS/409/1281 : Old star clusters in the FSR catalogue (Froebrich+, 2010) J/A+A/548/A122 : Berkeley 39 stars photometry and abundances (Bragaglia+, 2012) J/A+A/558/A53 : MW global survey of star clusters. II. (Kharchenko+, 2013) J/AJ/146/43 : WIYN open cluster study. LV. NGC 6819 (Platais+, 2013) J/ApJ/770/98 : Chandra study of NGC 6791 (van den Berg+, 2013) J/ApJS/208/9 : Intrinsic colors and temperatures of PMS stars (Pecaut+, 2013) J/AJ/150/97 : RVs in M67. I. 1278 candidate members (Geller+, 2015) J/ApJS/224/40 : Catalog of Chandra ACIS point like sources (Wang+, 2016) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Seq [1/151] Running sequence number (G1) 5 A1 --- f_Seq [d] Flag on Seq (1) 7- 21 A15 --- CXOU Official IAU identifier (HHMMSS.s+DDMMSS; J2000) 23- 32 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000) 34- 43 F10.6 deg DEdeg Declination in decimal degrees (J2000) 45- 48 F4.2 arcsec ePos [0.3/8] The 95% confidence radius (2) 50- 54 F5.2 arcmin theta [0.2/11] Angular offset (3) 56- 58 I3 ct CT [3/473] The 0.3-7keV net counts extracted 60- 61 I2 ct e_CT [2/22] The 1σ uncertainty in CT 63 A1 --- l_CS Limit flag on CS 64- 68 F5.1 ct CS [0/226] The 0.3-2keV net counts extracted 70- 71 I2 ct e_CS [1/15]? The 1σ uncertainty in CS 73- 78 F6.2 10-15mW/m2 FXu [0.5/100] Unabsorbed 0.3-7keV X-ray flux (4) 80- 83 F4.2 keV E50 [0.7/6] Median energy 85- 88 F4.2 keV e_E50 [0.06/2] The 1σ uncertainty in E50 90 A1 --- Match Optical counterpart match? (+ = present; - = absent; see table 2)
Note (1): d = detected by wavdetect using a sigthresh of 1e-6 but not with a sigthresh of 1e-7. Note (2): On wavdetect X-ray source position. Note (3): From our derived cluster center: RAJ2000=12:38:07.1, DE2000=-68:23:33 Note (4): For a 2keV MeKaL model and neutral hydrogen column of 1.9e21cm-2.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Seq [4/151] Sequence number (G1) 5- 14 A10 --- OID Optical identifier (1) 16 A1 --- f_OID [ac] Flag on OID (2) 18- 21 F4.2 arcsec Dox [0.05/8] Distance between X-ray and its optical counterpart 23- 28 F6.3 mag Vmag [11.4/23.8] Johnson V band magnitude 31 A1 --- f_Vmag [bd] Flag on Vmag (2) 33- 37 F5.3 mag B-V [0.5/2.1]? The (B-V) color index 39 A1 --- f_B-V [de] Flag on B-V (2) 41- 43 A3 --- Var Mazur+ (1995MNRAS.273...59M) short-period binary identifier; <Cl* Collinder 261 MKK VNN> in Simbad 45- 51 F7.5 d Per [0.2/2.2]? Period of short-period binary 52 A1 --- f_Per [?] Uncertainty flag on Per 54- 63 A10 --- VType Mazur+ (1995MNRAS.273...59M) variable type 65- 69 F5.2 10+23W LXu [0.5/25.5] Unabsorbed 0.3-7keV X-ray luminosity (3) 71- 75 F5.2 [-] logR [-4.8/0.3] Log ratio of X-ray to V band fluxes (4) 77- 81 A5 --- Class Classification (5)
Note (1): For five X-ray sources, viz. CX 7, CX 30, CX 40, CX 100, and CX 129, UCAC4 catalog IDs. These stars were saturated in our optical images and their photometry was obtained from the UCAC4 catalog. Note (2): Flag as follows: a = photometry of the source may be dubious due to image artifacts (CX81, CX65) or low S/N ratio (CX2, CX24, CX121); c = the optical counterpart lies just outside the 95% match radius, but within the 3σ match radius. b = The magnitude is a B magnitude. d = value obtained from Mazur+ (1995MNRAS.273...59M). e = B Magnitude obtained from USNO B1.0 catalogue (Monet+, 2003, I/284). Note (3): Assuming the source lies at the distance of the cluster, viz. 2.5kpc. Note (4): Unabsorbed X-ray (0.3-7keV) to optical (V band) flux ratio (2keV MeKaL model and neutral hydrogen column of 1.9e21cm-2). Note (5): Classification as follows: CV? = Candidate cataclysmic variable (12 occurrences); AB = Active binary (37 occurrences) AB? = Active binary candidate (8 occurrences); SSG = Sub-subgiant (3 occurrences); BSS = Blue straggler star (8 occurrences); YSS = Yellow straggler star (2 occurrences) Unc = Uncertain classification (51 occurrences); NM = Non-member (16 occurrences).
Global notes: Note (G1): CX NNN sorted by net X-ray counts (0.3-7keV).
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 24-Oct-2017
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