Slow Radiation-Driven Wind Solutions of A-Type Supergiants

TL;DR

This paper introduces a new slow wind solution for A-type supergiants that aligns theoretical predictions with observed mass loss rates and terminal velocities by considering slow rotation effects in radiation-driven wind models.

Contribution

It identifies a novel slow wind solution in radiation-driven wind models applicable to slowly rotating A-type supergiants, resolving previous discrepancies with observations.

Findings

New slow wind solutions match observed mass loss rates.

Terminal velocities are consistent with empirical data.

Wind momentum-luminosity relationship aligns with observations.

Abstract

The theory of radiation-driven winds succeeded in describing terminal velocities and mass loss rates of massive stars. However, for A-type supergiants the standard m-CAK solution predicts values of mass loss and terminal velocity higher than the observed values. Based on the existence of a slow wind solution in fast rotating massive stars, we explore numerically the parameter space of radiation-driven flows to search for new wind solutions in slowly rotating stars, that could explain the origin of these discrepancies. We solve the 1-D hydrodynamical equation of rotating radiation-driven winds at different stellar latitudes and explore the influence of ionization's changes throughout the wind in the velocity profile. We have found that for particular sets of stellar and line-force parameters, a new slow solution exists over the entire star when the rotational speed is slow or even zero. In the case of slow rotating A-type supergiant stars the presence of this novel slow solution at all latitudes leads to mass losses and wind terminal velocities which are in agreement with the observed values. The theoretical Wind Momentum-Luminosity Relationship derived with these slow solutions shows very good agreement with the empirical relationship. In addition, the ratio between the terminal and escape velocities, which provides a simple way to predict stellar wind energy and momentum input into the interstellar medium, is also properly traced.