Change of Binary Parameters: Evolutionary Scenarios of Binary Wolf-Rayet and He stars

Stellar Winds From Normal Stars

 

The effect of the normal star on the compact magnetized component is largely determined by the rate and velocity of stellar wind at infinity . For the majority of cases, we assume

where is the parabolic velocity at the stellar surface.

For Be-stars (i.e. those stars at the stage ``I'' whose mass increased during the first mass exchange), the wind velocity at infinity is taken to be equal to the Keplerian velocity  at the stellar surface

Thus, the lower stellar wind velocity leads to an effective increase of the captured mass rate by a secondary companion to such Be-stars.

The stellar wind rate at stage ``I'' is calculated as (de Jager 1980[41])

Here is a numerical coefficient.

For giant post-MS stars (stage ``II''), we assume and for massive star we take maximum wind rate between that given by de Jager's formula and that given by Lamers (1981)[94]:

For red supergiants at the asymptotic giant branch (AGB) stage, we use Reimers's formula (Kudritzki and Reimers, 1978[88])

When a massive star becomes a Wolf-Rayet star, its stellar wind can significantly increase (up to yr ). We parametrize such a wind  as

where the numerical coefficient is taken to be .