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D.M. Leeber, T.E. Harrison, B.J. McNamara (NMSU)
We have obtained infrared observations of several Soft X-ray Transients (SXTs). These binary systems are believed to consist of a normal late type dwarf star that fills its Roche Lobe, and a black hole. As the distorted companion star orbits the black hole, the observed flux rises and falls in a predictable manner. By modeling the "ellipsoidal variations" of the secondary star, we can determine the orbital period and inclination of the system. Observations in the near-infrared are better suited for detecting these ellipsoidal variations because the secondary star dominates the systemic luminosity and the contamination from the accretion disk is minimized. We have begun a program on the Apache Point Observatory 3.5 m telescope to observe all of the SXT systems visible from the northern hemisphere. We report our preliminary results on QZ Vul (GS 2000 +25), V518 Per (J0422+32), and V616 Mon (A0620-00). Our data for QZ Vul's color and orbital period are consistent with published values. Modeling of the ellipsoidal variations of QZ Vul suggests an orbital inclination of 70o.
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