Analytical solutions for radiation-driven winds in massive stars. II: The delta-slow regime

Abstract

Accurate mass-loss rates and terminal velocities from line-driven winds are important to obtain synthetic spectra from radiative transfer calculations. From a theoretical point of view, analytical expressions for the wind parameters and velocity profile would have many advantages over numerical calculations, that solve the complex non-linear set of hydrodynamic equations. In our previous work, we obtained an analytic description for the fast wind regime. Now, we propose a new analytical expression for the line-force term and obtain a velocity profile closed-form solution for the δ-slow regime. Using this analytical expression, we describe a methodology to obtain the mass-loss rates. Moreover, we establish a relation between our line-force term with the known stellar and m-CAK line force parameters. To this purpose, we calculate a grid of numerical hydrodynamical models and perform a multivariate multiple regression. The numerical and analytical descriptions lead to almost the same synthetic spectra.