Abstract
We have detected three new X-ray point sources, in addition to the known low-mass X-ray binary (LMXB) X1832-330, in the globular cluster NGC 6652 with a Chandra 1.6 ks HRC-I exposure. Star 49 (MV ~ 4.7), suggested by Deutsch and coworkers as the optical candidate for the LMXB, is identified (<03) not with the LMXB, but with another, newly detected source (B). Using archival Hubble Space Telescope (HST) images, we identify (<03) the LMXB (A) and one of the remaining new sources (C) with blue variable optical counterparts at MV ~ 3.7 and 5.3, respectively. The other new source (D) remains unidentified in the crowded cluster core. In the 0.5-2.5 keV range, assuming a 5 keV thermal bremsstrahlung spectrum and NH = 5.5 × 1020, source A has intrinsic luminosity LX ~ 5.3 × 1035 ergs s-1. Assuming a 1 keV thermal bremsstrahlung spectrum, B has LX ~ 4.1 × 1033 ergs s-1, while C and D have LX ~ 8 × 1032 ergs s-1. Source B is probably a quiescent LMXB, while source C may be either a luminous cataclysmic variable or a quiescent LMXB.
Highlights
Globular clusters have proven to be an excellent place to study stellar populations, dynamic evolution, and binary systems. Their high stellar densities allow their populations of white dwarfs and neutron stars to interact with cluster primordial binaries by exchange collisions (Hut et al 1992)
X-ray studies of globular clusters are e†ective at studying both compact objects and compact binaries
Successful searches for low-mass X-ray binary (LMXB) optical counterparts have been undertaken for several clusters (Deutsch, Anderson, & Margon 1998a and references therein ; Homer et al 2001)
Summary
Globular clusters have proven to be an excellent place to study stellar populations, dynamic evolution, and binary systems. Successful searches for low-mass X-ray binary (LMXB) optical counterparts have been undertaken for several clusters (Deutsch, Anderson, & Margon 1998a and references therein ; Homer et al 2001). A search for the optical counterpart of the LMXB was undertaken by Deutsch, Margon, & Anderson (1998b ; hereafter DMA98), not including the entire ROSAT error circle for the LMXB. They were able to identify a plausible candidate (star 49) ; it is located 2.3 p from the ROSAT position and is identiÐed here with a lower luminosity source. We use Hubble Space T elescope (HST ) archival images to identify optical counterparts
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