The chromospheric Ca II and Mg II radiative losses in late-type stars: a computational comparison between two-level and multi-level atomic models

Abstract

In the current study we present radiation correction factors to compute the radiative losses by Mg II and Ca II ions during the process of constructing theoretical models for the chromospheres in late-type stars (spectral type in the range F5V-K8V). We combine the two-level atom approach with the multi-level atom method to accurately compute the radiation correction factors. The procedure is fast and reasonably accurate to be implemented in the time-dependent computations. In the current computations we implement what is called pseudo-partial frequency redistribution and the time-dependent ionization in regard to hydrogen. The radiative correction factors for Mg II show very slight variation for the different spectral types with average value of 1.5. The values we obtained for Ca II show very strong dependence on spectral types and the basic parameters, with values range between 5.58 to 4.22 for F5V and K8V spectral types, respectively. The obtained results accelerate the process of constructing theoretical model chromospheres based on mechanical heating by monochromatic and wave spectra. The current study is an initial step in establishing hybrid multi-dimensional models of stellar chromospheres.