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D.M. Gelino (CASS / UCSD)
We present an observational study of four Soft X-ray Transient (SXT) systems (GU Mus, V616 Mon, J0422+32, and QZ Vul), with the goal of precisely determining their orbital inclination angles and primary object masses. We observe these systems in the near-infrared, and model their ellipsoidal variations based upon their geometries and non-uniform surface brightnesses. We find that the secondary stars in these systems generally have masses and radii that differ from those of ``normal'' main sequence stars: However, several of the secondaries seem to exhibit properties of stellar spots on their surfaces, consistent with late type dwarfs. We determine that the shape of the stellar black hole mass distribution is broader than previously thought, and that SXT accretion disks are effectively invisible in the infrared. In comparing the newly refined properties of these SXTs, several correlations present themselves. The SXT optical outburst magnitude appears to be directly correlated with the observable area of the accretion disk, while the outburst x-ray luminosity is strongly inversely correlated with the mass of the black hole. The time of the secondary x-ray maximum also appears to be inversely correlated with the mass of the black hole. Possible implications of these correlations are discussed.
The author(s) of this abstract have provided an email address for comments about the abstract: dgelino@ucsd.edu