Albert K. H. Kong et al. 2006 ApJ 647 1065 doi:10.1086/505485
Albert K. H. Kong1, Cees Bassa2, David Pooley3,4, Walter H. G. Lewin1, Lee Homer5, Frank Verbunt2, Scott F. Anderson5 and Bruce Margon6
Show affiliationsWe report on the Chandra X-Ray Observatory observations of the globular cluster NGC 288. We detect four X-ray sources within the core radius and seven additional sources within the half-mass radius down to a limiting luminosity of LX = 7 × 1030 ergs s-1 (assuming cluster membership) in the 0.3-7 keV band. We also observed the cluster with the Hubble Space Telescope Advanced Camera for Surveys and identify optical counterparts to seven X-ray sources out of the nine sources within the HST field of view. Based on the X-ray and optical properties, we find 2-5 candidates of cataclysmic variables (CVs) or chromospherically active binaries and 2-5 background galaxies inside the half-mass radius. Since the core density of NGC 288 is very low, the number of faint X-ray sources of NGC 288 found in the Chandra and HST observations is higher than the prediction on the basis of the collision frequency. We suggest that the CVs and chromospherically active binaries are primordial in origin, in agreement with the theoretical expectation.
binaries: close; globular clusters: individual (NGC 288); novae, cataclysmic variables; X-rays: binaries
Issue 2 (2006 August 20)
Received 2006 March 9, accepted for publication 2006 April 28
Albert K. H. Kong et al. 2006 ApJ 647 1065
Eva Noyola et al. 2008 ApJ 676 1008
The SDSS Collaboration et al. 2000 The Astronomical Journal 120 1198
Paul J. Francis et al. 2004 ApJ 614 75
D. J. Fixsen et al. 1998 ApJ 508 123
Bing Zhang and Peter Mészáros 2002 ApJ 571 876
Renato A. Dupke et al. 2007 ApJ 668 781
Povilas Palunas et al. 2004 ApJ 602 545
B. Willems et al 2007 ApJ 665 L59
S. M. Ransom et al 2004 ApJ 609 L71