SIMBAD references

We present results from quantitative modeling and spectral analysis of the high-mass X-ray binary system Vela X-1 obtained with the Chandra HETGS. The spectra exhibit emission lines from H- and He-like ions driven by photoionization, as well as fluorescent emission lines from several elements in lower charge states. The properties of these X-ray lines are measured with the highest accuracy to date. In order to interpret and make full use of the data, we have developed a simulator, which calculates the ionization structure of a stellar wind and performs Monte Carlo simulations of X-ray photons propagating through the wind. From comparisons of the observed spectra with results from the simulator, we are able to find the ionization structure and the geometrical distribution of material in the stellar wind that can reproduce the observed spectral line intensities and continuum shapes remarkably well. We find that the stellar wind profile can be represented by a CAK model with a star mass-loss rate of (1.5-2.0)x10^–6 M_☉/yr, assuming a terminal velocity of 1100 km/s. It is found that a large fraction of emission lines from highly ionized ions are formed in the region between the neutron star and the companion star. We also find that the fluorescent lines must be produced in at least three distinct regions: the extended stellar wind, reflection off the stellar photosphere, and in a distribution of dense material partially covering and possibly trailing the neutron star, which may be associated with an accretion wake. Finally, from detailed analysis of the emission-line profiles, we demonstrate that the stellar wind dynamics is affected by X-ray photoionization.