Timing Studies of X-Ray Binary Orbits
NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
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X-ray astronomy, by necessity, involves the study of highly variable stars, nearly all of them in binary systems where one member is a compact object such as a neutron star or black hole. These systems allow us to probe physical effects in regions of extreme gravity, high temperatures, and intense magnetic fields that are characteristic of compact objects and are unattainable in laboratory experiments. By studying the brightness variations and eclipses using space-based X-ray telescopes, we can determine the binary system orbital parameters and characteristics of the mass transfer that powers these variations. This, in turn, allows us ultimately to understand better the evolution of these exotic binary systems. Here we describe two such studies carried out at NRL the discovery of the orbit of a neutron star orbiting a hot supergiant star, and the surprising orbital period evolution observed in a lowmass X-ray binary.