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arXiv · 0903.4164

The Quiescent Optical and Infrared Counterpart to EXO 0748-676 = UY Vol

R. I. Hynes·E. D. Jones
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Abstract

We present optical and infrared photometry of the low-mass X-ray binary EXO 0748-676 in quiescence for the first time in 24 years since it became X-ray active in 1985. We find the counterpart at average magnitudes of R=22.4 and J=21.3. We monitored the source approximately nightly through 2008 November to 2009 January. During this time there was considerable night-to-night optical variability but no long term trends were apparent. The night-to-night variability reveals a periodicity of P=0.159331+/-0.000012d, consistent with the X-ray orbital period to within 0.01%. This indicates that the quiescent optical modulation is indeed orbital in nature rather than a superhump. Interestingly, the modulation remains single-peaked with a deep minimum coincident with the times of X-ray eclipse, and there is no indication of a double-peaked ellipsoidal modulation. This indicates that even in `quiescence' emission from the accretion disk and/or X-ray heated inner face of the companion star dominate the optical emission, and implies that obtaining an accurate dynamical mass estimate in quiescence will be challenging.

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R. I. Hynes, E. D. Jones. 2009-03-24. The Quiescent Optical and Infrared Counterpart to EXO 0748-676 = UY Vol. https://doi.org/10.1088/0004-637x%2F697%2F1%2Fl14

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