Multicomponent radiatively driven stellar winds

II. Gayley-Owocki heating in multitemperature winds of OB stars

¹ Ústav teoretické fyziky a astrofyziky PřF MU, Kotlářská 2, 611 37 Brno, Czech Republic
² Astronomický ústav, Akademie věd České republiky, 251 65 Ondřejov, Czech Republic

Corresponding author: J. Krtička, krticka@physics.muni.cz

Received: 29 May 2001
Accepted: 24 July 2001

Abstract

We show that the so-called Gayley-Owocki (Doppler) heating is important for the temperature structure of the wind of main sequence stars cooler than the spectral type O6. The formula for Gayley-Owocki heating is derived directly from the Boltzmann equation as a direct consequence of the dependence of the driving force on the velocity gradient. Since Gayley-Owocki heating deposits heat directly on the absorbing ions, we also investigated the possibility that individual components of the radiatively driven stellar wind have different temperatures. This effect is negligible in the wind of O stars, whereas a significant temperature difference takes place in the winds of main sequence B stars for stars cooler than B2. Typical temperature differences between absorbing ions and other flow components for such stars is of the order . However, in the case when the passive component falls back onto the star, the absorbing component reaches temperatures of order , which allows for emission of X-rays. Moreover, we compare our computed terminal velocities with the observed ones. We found quite good agreement between predicted and observed terminal velocities. The systematic difference coming from the using of the so called "cooking formula" has been removed.