Line-Driven Winds Revisited in the Context of Be Stars: $\Omega$-slow Solutions with High $k$ Values

TL;DR

This study revisits line-driven wind models for Be stars, demonstrating that $\Omega$-slow solutions with high $k$ values produce slower, denser outflows consistent with observed Be star disks, expanding understanding of stellar wind dynamics.

Contribution

The paper introduces and analyzes $\Omega$-slow solutions with high $k$ values, showing they can explain Be star disks better than standard solutions.

Findings

$\Omega$-slow solutions match observed Be star outflow velocities.

High $k$ values lead to denser, slower winds similar to Be star disks.

New wind behaviors emerge at very high $k$ values.

Abstract

The standard, or fast, solutions of m-CAK line-driven wind theory cannot account for slowly outflowing disks like the ones that surround Be stars. It has been previously shown that there exists another family of solutions --- the $\Omega$-slow solutions --- that is characterized by much slower terminal velocities and higher mass-loss rates. We have solved the one-dimensional m-CAK hydrodynamical equation of rotating radiation-driven winds for this latter solution, starting from standard values of the line force parameters ($\alpha$, $k$, and $\delta$), and then systematically varying the values of $\alpha$ and $k$. Terminal velocities and mass-loss rates that are in good agreement with those found in Be stars are obtained from the solutions with lower $\alpha$ and higher $k$ values. Furthermore, the equatorial densities of such solutions are comparable to those that are typically assumed in ad hoc models. For very high values of $k$, we find that the wind solutions exhibit a new kind of behavior.