Radiation driven winds with rotation: The oblate finite disc correction factor

TL;DR

This paper models stellar winds considering stellar oblateness due to rotation, revealing significant polar acceleration and equatorial density enhancements that could explain observed features of Be stars.

Contribution

It introduces a modified finite disk correction factor accounting for stellar oblateness in the m-CAK wind model, providing new insights into wind structure of rotating stars.

Findings

Polar wind is faster due to larger stellar surface area.

Equatorial wind is slower and denser, with density contrast around 100.

Results may explain long-standing Be star phenomena.

Abstract

We have incorporated the oblate distortion of the shape of the star due to the stellar rotation, which modifies the finite disk correction factor (f_D) in the m-CAK hydrodynamical model. We implement a simplified version for the f_D allowing us to solve numerically the non-linear m- CAK momentum equation.We solve this model for a classical Be star in the polar and equatorial directions. The star's oblateness modifies the polar wind, which is now much faster than the spherical one, mainly because the wind receives radiation from a larger (than the spherical) stellar surface. In the equatorial direction we obtain slow solutions, which are even slower and denser than the spherical ones. For the case when the stellar rotational velocity is about the critical velocity, the most remarkable result of our calculations is that the density contrast between the equatorial density and the polar one, is about 100. This result could explain a long-standing problem on Be stars.