Asymmetric Shapes of Radio Recombination Lines from Ionized Stellar Winds

Abstract

Recombination line profile shapes are derived for ionized spherical stellar winds at radio wavelengths. It is assumed that the wind is optically thick owing to free-free opacity. Emission lines of arbitrary optical depth are obtained assuming that the free-free photosphere forms in the outer, constant expansion portion of the wind. Previous works have derived analytic results for isothermal winds when the line and continuum source functions are equal. Here, semi-analytic results are derived for when the source functions are not equal to reveal that line shapes can be asymmetric about line center. A parameter study is presented and applications discussed.