The Eclipsing Black Hole X-ray Binary M33 X-7: Understanding the Current Properties
Hot and Cool: Bridging Gaps in Massive Star Evolution ASP Conference Series Vol. 425, Proceedings of a Workshop held at the California Institute of Technology, Pasadena, California, 10-12 November 2008. Edited by Claus Lietherer, Philip Bennett, Pat Morris, Jacco van Loon. San Francisco: Astronomical Society of the Pacific, 2010., p.227
We explore the formation and evolution of the black hole X-ray binary system M33 X-7. In particular, we examine whether accounting for systematic errors in the stellar parameters inherent to single star models, as well as the uncertainty in the distance to M33, can explain the discrepancy between the observed and expected luminosity of the ˜70 Msun companion star. Our analysis assumes no prior interactions between the companion star and the black hole progenitor. We use four different stellar evolution codes, modified to include a variety of current stellar wind prescriptions. For the models satisfying the observational constraints on the donor star’s effective temperature and luminosity, we recalculate the black hole mass, the orbital separation, and the mean X-ray luminosity. Our best model, satisfying simultaneously all observational constraints except the observationally inferred companion mass, consists of a ˜13 Msun black hole and a ˜54 Msun companion star. We conclude that a star with the observed mass and luminosity can not be explained via single star evolution models, and that a prior interaction between the companion star and the black hole progenitor should be taken into account.