Document Type

Article

Publication Date

2-1-2013

Abstract

We present phase-resolved spectroscopy and photometry of a source discovered with the Chandra Galactic Bulge Survey (GBS), CXOGBS J174444.7-260330 (aka CX93 and CX153 in the previously published GBS list). We find two possible values for the orbital period P, differing from each other by ~13 s. The most likely solution is P = 5.690 14(6) h. The optical lightcurves show ellipsoidal modulations, whose modelling provides an inclination of 32±1° for the most likely P. The spectra are dominated by a K5 V companion star (the disc veiling is 5 per cent). Broad and structured emission from the Balmer lines is also detected, as well as fainter emission from He I. From the absorption lines we measure K2 = 117 ± 8kms-1 and v sin i = 69 ± 7kms-1. By solving the system mass function we find M1 = 0.8 ± 0.2 M⊙ for the favoured P and i, consistent with a white dwarf accretor, and M2 = 0.6 ± 0.2 M⊙. We estimate a distance in the range 400-700 pc. Although in a low accretion state, both spectroscopy and photometry provide evidence of variability on a time-scale of months or faster. Besides finding a new, long orbital period cataclysmic variable (CV) in a low accretion state, this work shows that the design of the GBS works efficiently to find accreting X-ray binaries in quiescence, highlighting that the spectra of CVs in a low accretion state can at times appear suggestive of a quiescent neutron star or a black hole system. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Publication Source (Journal or Book title)

Monthly Notices of the Royal Astronomical Society

First Page

3543

Last Page

3550

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