Abstract
We report our analysis of a Chandra X-ray observation of the rich globular cluster M80, in which we detect some 19 sources to a limiting 0.5-2.5 keV X-ray luminosity of 7*10^30 ergs/s within the half-mass radius. X-ray spectra indicate that two of these sources are quiescent low-mass X-ray binaries (qLMXBs) containing neutron stars. We identify five sources as probable cataclysmic variables (CVs), one of which seems to be heavily absorbed, implying high inclination. The brightest CV may be the X-ray counterpart of Nova 1860 T Sco. The concentration of the X-ray sources within the cluster core implies an average mass of 1.2+/-0.2 Msun, consistent with the binary nature of these systems and very similar to the radial distribution of the blue stragglers in this cluster. The X-ray and blue straggler source populations in M80 are compared to those in the similar globular cluster 47 Tuc.
Highlights
The Chandra X-Ray Observatory has allowed rapid gains in the study of X-ray sources in globular clusters, especially when combined with the resolution of the Hubble Space Telescope (HST)
A few of these had been identified with bright low-mass X-ray binaries (LMXBs) in quiescence or with cataclysmic variables (Cool et al 1995)
We identify probable cataclysmic variables (CVs), qLMXBs, and unidentified sources with ~, Â, and ? symbols, respectively, in Figures 2 and 3
Summary
The Chandra X-Ray Observatory has allowed rapid gains in the study of X-ray sources in globular clusters, especially when combined with the resolution of the Hubble Space Telescope (HST). The spectral and luminosity signatures of qLMXBs, thought to emit thermal radiation from the neutron star surface (Brown, Bildsten, & Rutledge 1998), allow them to be identified (Rutledge et al 2002; GHE01b) These advances make it practical to compare significant populations of X-ray sources in different globular clusters, exploring similarities or differences in properties or formation mechanisms (see Pooley et al 2003; Heinke et al 2003c). We present new Chandra observations of the globular cluster M80 (NGC 6093) This globular cluster has a small core radius (6>5; Ferraro et al 1999) and relatively high central density [logð0Þ 1⁄4 4:87, computed using the prescription of Djorgovski 1993], it is not corecollapsed. We discuss our findings and compare them to 47 Tuc in x 3 and provide a summary in x 4
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