Massive stars and their compact remnants in high-mass x-ray binaries

In a high-mass X-ray binary (HMXB) a massive star interacts with a neutron-star or black-hole companion in various ways. The gravitational interaction enables the measurement of fundamental parameters such as the mass of both binary components, providing important constraints on the evolutionary history of the system, the equation of state of matter at supra-nuclear density, and the supernova mechanism. The stellar wind of the massive star is intercepted by the strong gravitational field of the compact companion, giving rise to the production of X-rays. The X-rays increase the degree of ionization in a small to very extended region of the surrounding stellar wind, depending on the X-ray luminosity. This has observable consequences for the structure and dynamics of the accretion flow. In this paper we concentrate on the fundamental parameters of the most massive HMXBs, i.e. those with an OB supergiant companion, including some systems exhibiting relativistic jets ("microquasars").