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Post Info TOPIC: XB1832-330
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XB1832-330
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Title: A 2.15 Hour Orbital Period for the Low Mass X-Ray Binary XB 1832-330 in the Globular Cluster NGC 6652
Authors: Megan C. Engel (1), Craig O. Heinke (1), Gregory R. Sivakoff (1), Khaled G. Elshamouty (1), Peter D. Edmonds (2) ((1) U of Alberta (2) Harvard-Smithsonian Centre for Astrophysics)

We present a candidate orbital period for the low mass X-ray binary XB 1832-330 in the globular cluster NGC 6652 using a 6.5 hour Gemini South observation of the optical counterpart of the system. Light curves in g' and r' for two LMXBs in the cluster, sources A and B in previous literature, were extracted and analyzed for periodicity using the ISIS image subtraction package. A clear sinusoidal modulation is evident in both of A's curves, of amplitude ~0.11 magnitudes in g' and ~0.065 magnitudes in r', while B's curves exhibit rapid flickering, of amplitude ~1 magnitude in g' and ~0.5 magnitudes in r'. A Lomb-Scargle test revealed a 2.15 hour periodic variation in the magnitude of A with a false alarm probability less than 10^-11, and no significant periodicity in the light curve for B. Though it is possible saturated stars in the vicinity of our sources partially contaminated our signal, the identification of A's binary period is nonetheless robust.

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Title:  XMM-Newton observations of the low-mass X-ray binary XB1832-330 in the galactic globular cluster NGC 6652
Authors: L. Sidoli (1), N. La Palombara (1), T. Oosterbroek (2), A.N. Parmar (3) ((1)-INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Milano, Italy (2)-Science Payload and Advanced Concepts Office, ESA, ESTEC, Noordwijk, The Netherlands; (3)-Research and Scientific Support Department of ESA, ESTEC, Noordwijk, The Netherlands)

We report on two XMM-Newton observations performed in 2006 of the luminous low-mass X-ray binary XB1832-330 which is located in the galactic globular cluster NGC 6652 and is probably an ultracompact binary (orbital period less than 1 hour). The aim of these observations is to investigate the low-energy absorption towards NGC6652 and in particular to search for Ne-rich material local to the binary, which has been suggested as a possible spectral signature of Neon rich degenerate companions. XMM-Newton observed the source twice, in 2006 September and October. High resolution spectroscopy with the RGS was used to estimate the ratio of the neutral neon to oxygen column densities to search for an anomalous Ne abundance in this X-ray binary. We find no evidence for anomalous Ne/O ratios, finding Ne/O=0.18±0.06 and Ne/O=0.17±0.03 (1 sigma uncertainties), in the two observations, respectively. These values are consistent with that in the interstellar medium. Timing analysis of EPIC data suggests possible periodicities at 9170±235 s and 18616 ± 531 s, which need confirmation. A by-product of these observations consists of the spatial analysis of the source field, which resulted in the detection of 46 faint sources within the EPIC field of view, which are not present in the Second XMM-Newton Serendipitous Source Catalogue. All these faint sources are likely foreground objects. We performed the first high spectral resolution observations of XB1832-33, a probable ultracompact binary, without finding any evidence for an anomalous Ne abundance.

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