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2003ApJ...596.1197E - Astrophys. J., 596, 1197-1219 (2003/October-3)
An extensive census of Hubble space telescope counterparts to Chandra X-ray sources in the globular cluster 47 Tucanae. II. Time series and analysis.
EDMONDS P.D., GILLILAND R.L., HEINKE C.O. and GRINDLAY J.E.
Abstract (from CDS):
The radial distribution of the X-ray detected active binaries is indistinguishable from that of the much larger sample of optical variables (eclipsing and contact binaries and BY Dra variables) detected in previous Wide Field Planetary Camera 2 (WFPC2) studies by Albrow et al. The X-ray properties of these objects (luminosity, hardness ratios, and variability) are consistent with those of active binaries found in field studies, and the FX/Foptdistribution is significantly different from those of the CVs and the MSPs that are detected (or possibly detected) in the optical. Despite these results, we examine the possibility that a few of the active binaries are MSPs with main-sequence companions resulting from double exchanges in the crowded core of 47 Tuc. No solid evidence is found for a significant population of such objects, and therefore, using the methods of Grindlay et al., we estimate that the number of MSPs in 47 Tuc with luminosities above 1030 ergs/s is ∼30-40, near the previous lower limit. We present the results of a new, deeper search for faint low-mass X-ray binaries (LMXBs) in quiescence. One reasonable and one marginal candidate for optical identification of a quiescent LMXB was found (one is already known). Finally, it is shown that the periods of the blue variables showing little or no evidence for X-ray emission are too long for Roche lobe filling (if the variations are ellipsoidal). These blue variables also show no evidence for the large flickering levels seen in comparably bright CVs. At present we have no satisfactory explanation for these objects, although some may be detached white dwarf-main-sequence star binaries.
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Journal keyword(s): Stars: Binaries: General - Galaxy: Globular Clusters: Individual: Name: 47 Tucanae - Stars: Novae, Cataclysmic Variables - Techniques: Photometric - X-Rays: Binaries
Simbad objects: 116
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