J/ApJ/700/1702 ChaMPlane deep galactic bulge survey. I. (van den Berg+, 2009)
ChaMPlane deep galactic bulge survey. I. Faint accretion-driven binaries in the limiting window. van den Berg M., Hong J., Grindlay J.E. <Astrophys. J., 700, 1702-1715 (2009)> =2009ApJ...700.1702V
ADC_Keywords: Binaries, cataclysmic ; X-ray sources ; Surveys ; Photometry, HST Keywords: Galaxy: bulge - novae, cataclysmic variables - surveys - X-rays: binaries Abstract: We have carried out a deep X-ray and optical survey with Chandra and HST of low-extinction regions in the Galactic bulge. Here we present the results of a search for low-luminosity (LX≲1034erg/s) accreting binaries among the Chandra sources in the region closest to the Galactic center, at an angular offset of 1.4°, that we have named the Limiting Window (LW). Based on their blue optical colors, excess Hα fluxes, and high X-ray-to-optical flux ratios, we identify three likely accreting binaries; these are probably white dwarfs accreting from low-mass companions (cataclysmic variables; CVs) although we cannot exclude that they are quiescent neutron-star or black-hole low-mass X-ray binaries. Distance estimates put these systems farther than ≳2kpc. Based on their Hα-excess fluxes and/or high X-ray-to-optical flux ratios, we find 22 candidate accreting binaries; however, the properties of some can also be explained if they are dMe stars or active galaxies. Description: As part of the Chandra Multi-wavelength Plane survey (ChaMPlane; Grindlay et al. 2005ApJ...635..920G), we have carried out an X-ray and optical survey of deep, near-simultaneous Chandra and HST pointings of three low-extinction regions, or windows, in the Galactic bulge. The Limiting Window (LW) was observed with the Chandra/ACIS-I aimpoint placed at Galactic coordinates (l,b)= (0.10°,-1.43°). Due to observatory constraints, the observation was split in three exposures: ObsID 6362 (2005 August 19, 38ks), ObsID 5934 (2005 August 22, 41ks), and ObsID 6365 (2005 October 25, 21ks). We observed with HST the inner area of the ACIS field on the Advanced Camera for Surveys (ACS). The observations (program GO-10353) were carried out simultaneous with the first Chandra exposure (2005 Aug 19). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 31 100 Chandra sources in the ACS field of view table3.dat 120 13 *Candidate accreting binaries in the LW selected on optical colors table4.dat 120 12 Candidate accreting binaries in the LW selected on intrinsic X to optical flux ratio table5.dat 120 21 *Other identifications of Chandra sources in the LW
Note on table3.dat: Properties of our best candidate CVs (LW 1-4) and the more marginal candidates (LW 5-13). Note on table5.dat: Properties of the likely coronal source identifications (LW26-43) discussed in Section 4.2.
See also: B/chandra : The Chandra Archive Log (CXC, 1999-) B/hst : HST Archived Exposures Catalog (STScI, 2007) I/315 : UCAC3 Catalogue (Zacharias+ 2009) II/213 : OGLE Galactic Bulge periodic variables (Udalski+ 1996) J/ApJ/685/463 : ChaMPlane X-ray sources in the Galactic bulge (Koenig+, 2008) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 15 A15 --- CXOPS Source name (HHMMSS.s+DDMMSS; J2000) 17 A1 --- f_CXOPS [a] Source partly in chip gap (1) 19 A1 --- l_SNRh [-] The source was not significantly detected in the hard band 20- 23 F4.2 --- SNRh Hard (2-8keV) band signal-to-noise ratio 25- 26 A2 --- --- [LW] 28- 29 I2 --- LW [1/43]? LW identifier if in Limiting Window 31 I1 --- T [3,5]? table number (3+4 = accreting binary candidates; 5 = other optical sources)
Note (1): a = The 95% error radius of this source lies partly in the ACS chip gap.
Byte-by-byte Description of file: table3.dat table4.dat table5.dat
Bytes Format Units Label Explanations
1- 2 A2 --- --- [LW] 4- 5 I2 --- LW [1/43] Source name <[VHG2009] LW NN> in Simbad 6 A1 --- u_LW [b] Ambiguous identification (1) 8- 22 A15 --- CXOPS Chandra source name (HHMMSS.s+DDMMSS; J2000) 24- 26 I3 ct Cts Net source counts in the Bx band (0.3-8keV) 28- 29 I2 ct e_Cts Cts uncertainty 31- 34 F4.2 keV E50 ? Median energy E50 in the Bx band 36- 39 F4.2 keV e_E50 ? E50 uncertainty 41 I1 --- Gp [1,3] Quantile spectral group (4) 43- 44 I2 h RAh ? Optical hour of right ascension (J2000) (2) 46- 47 I2 min RAm ? Optical minute of right ascension (J2000) 49- 54 F6.3 s RAs ? Optical second of right ascension (J2000) 56 A1 --- DE- Optical sign of declination (J2000) (2) 57- 58 I2 deg DEd ? Optical degree of declination (J2000) 60- 61 I2 arcmin DEm ? Optical arcminute of declination (J2000) 63- 67 F5.2 arcsec DEs ? Optical arcsecond of declination (J2000) 69- 73 F5.2 mag R625 ? HST/ACS R-band magnitude (F625W) unless flagged (not for table 4) 74 A1 --- f_R625 [a] Flag on R625 (3) 76- 80 F5.2 mag B435 ? HST/ACS B-band magnitude (F435W) (not for table 4) 82- 86 F5.2 mag Ha ? Hα magnitude (not for table 4) 88- 92 F5.2 [-] logX/R Ratio of the observed (log(f_X_/f_R_)) X-ray and optical fluxes (4) 94- 97 F4.2 [-] e_logX/R logX/R uncertainty (4) 98 A1 --- f_logX/R [acd] Flag on logX/R (3) 100-104 F5.2 [-] logX/Ru Ratio of the intrinsic (log(f_X_/f_R_)_u_) X-ray and optical fluxes (4) 106-109 F4.2 [-] e_logX/Ru logX/Ru uncertainty (4) 110 A1 --- f_logX/Ru [acd] Flag on logX/Ru (3) 112-120 A9 --- Com Comment
Note (1): The identification of the OGLE variable in the ACS image is ambiguous; therefore we list both candidate optical counterparts. Note (2): Optical positions are not given for table 4. Errors in the absolute astrometry are ∼0.095". Note (3): Flag as follows: a = LW 26 and LW 27 are saturated in our ACS images. In Column R625 we give the UCAC2 magnitude from Zacharias et al. (2004, Cat. I/289; obsoleted by I/315) that is between V and R, and use it to compute the X-ray-to-optical flux ratios. c = The optical source is saturated in the F625W image; we assume R625=Hα to compute the X-ray-to-optical flux ratios. d = The optical source is not detected in the F625W and Hα images; we use B435 to compute the X-ray-to-optical flux ratios. Note (4): Fluxes are corrected for extinction using the group-specific nH values below: -------------------------------------------------- Gp Model Parameter nH (1022atoms/cm2) -------------------------------------------------- 1 MeKaL kT=1keV 0.76 2 power law Γ=1.28 0.76 3 power law Γ=1.21 1.95 -------------------------------------------------- Quoted errors in the flux ratios only include a contribution from errors in the X-ray counts, not from systematic errors.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 10-Aug-2011
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