The Nature of the Emission Spectrum of NGC 7793 P13: modeling the atmosphere of the donor star

Abstract

We continue to study the ultra-luminous X-ray source NGC 7793 P13 in the optical range. In this work, we are testing the model of a spherically symmetric wind atmosphere of the donor star, previously identified as a B9 Ia supergiant. The model spectrum has shown good agreement with the observed one at a relatively high mass loss rate of $\dot{M}\approx 6\times 10^{-6}{M}_{\odot }{\text{yr}}^{-1}$; other parameters turned out to be close to those expected for late B-supergiants. The increased mass loss rate can be explained by the high rotation velocity of the star. In addition, we have qualitatively demonstrated the effect of X-ray irradiation on the observed spectrum and discuss the fundamental possibility of wind acceleration under conditions of powerful irradiation.

17 pages, 6 figure; Accepted for publication in Astrophysical Bulletin