The structure of blue supergiant winds and the accretion in supergiant High Mass X-ray Binaries

TL;DR

This paper presents a model of OB supergiant stellar winds with clumps to explain the X-ray variability in High Mass X-ray Binaries, successfully reproducing observed light curves and suggesting lower mass loss rates than previous homogeneous wind estimates.

Contribution

The study introduces a clumpy wind model for OB supergiants that accounts for observed X-ray variability in HMXBs, improving understanding of wind structure and accretion processes.

Findings

Model reproduces observed X-ray light curves of HMXBs.

Clumpy wind model indicates lower mass loss rates than homogeneous wind assumptions.

Variability depends on orbital parameters and wind characteristics.

Abstract

We have developed a stellar wind model for OB supergiants to investigate the effects of accretion from a clumpy wind on the luminosity and variability properties of High Mass X-ray Binaries. Assuming that the clumps are confined by ram pressure of the ambient gas and exploring different distributions for their mass and radii, we computed the expected X-ray light curves in the framework of the Bondi-Hoyle accretion theory, modified to take into account the presence of clumps. The resulting variability properties are found to depend not only on the assumed orbital parameters but also on the wind characteristics. We have then applied this model to reproduce the X-ray light curves of three representative High Mass X-ray Binaries: two persistent supergiant systems (VelaX-1 and 4U1700-377) and the Supergiant Fast X-ray Transient IGRJ11215-5952. The model can reproduce well the observed light curves, but requiring in all cases an overall mass loss from the supergiant about a factor 3-10 smaller than the values inferred from UV lines studies that assume a homogeneous wind.