The stellar wind velocity field of HD 77581

Abstract

The early acceleration of stellar winds in massive stars is poorly constrained. The scattering of hard X-ray photons emitted by the pulsar in the high-mass X-ray binary Vela X-1 can be used to probe the stellar wind velocity and density profile close to the surface of its supergiant companion HD 77581. We built a high signal-to-noise and high resolution hard X-ray lightcurve of Vela X-1 measured by Swift/BAT over 300 orbital periods of the system and compared it with the predictions of a grid of hydrodynamic simulations. We obtain a very good agreement between observations and simulations for a narrow set of parameters, implying that the wind velocity close to the stellar surface is twice larger than usually assumed with the standard beta law. Locally a velocity gradient of $\beta \sim 0.5$ is favoured. Even if still incomplete, hydrodynamic simulations are successfully reproducing several observational properties of Vela X-1.

submitted to A&A, comments are welcome

References in corpus (6)

• Mass loss from hot massive stars
• Probing clumpy stellar winds with a neutron star
• High variability in Vela X-1: giant flares and off states
• Origin of the X-ray off-states in Vela X-1
• Revisiting the Flip-Flop Instability of Hoyle-Lyttleton Accretion
• Neutron star masses from hydrodynamical effects in obscured sgHMXBs

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