X-ray Spectroscopy of Accretion Disks and Stellar Winds in X-Ray Binaries

From hot, tenuous gas dominated by Compton processes, to warm, photoionized emission-line regions, to cold, optically thick fluorescing matter, accreting gas flows in X-ray binaries span a huge portion of the parameter space accessible to astrophysical plasmas. The coexistence of such diverse states of material within small volumes (10–10 cm) leaves X-ray spectroscopists with a challenging set of problems, since all such matter produces various X-ray spectral signatures when exposed to hard X rays. Emission-line regions in X-ray binaries are characterized by high radiation energy densities, relatively high particle densities, and velocities ∼ 1000 km s−1. In this article, we describe some recent efforts to generate detailed X-ray line spectra from models of X-ray binaries, whose aims are to reproduce spectra acquired with the ASCA, Chandra, and XMM-Newton observatories. With emphasis on the global nature of X-ray line emission in these systems, the article includes separate treatments of high-mass and low-mass systems, as well as summaries of continuum spectroscopy and plasma diagnostics.