Calculations of hydrogen and helium line emission for conditions in stellar chromospheres

Abstract

We perform calculations of the intensities of hydrogen Balmer lines and the HeI λ 5876 line. The input gas parameters such as temperature, concentration, and column density correspond to solar and solar-type star atmospheres. The influence of fast particles (electrons) is also considered. The radiative transfer in spectral line frequencies is treated in the frame of the Sobolev – Biberman – Holstein approximation in such a way that hydrogen lines have the convolution of the Doppler and Holtzmark profiles, and helium lines have the Voigt profile. In equations describing the hydrogen and the helium energy level occupation, the terms encompass the rates of bound-bound, bound-free radiative and collisional processes. The Balmer decrement in cold gas (6000 K) is quite steep without fast particles, being sloping with fast particles. In warm gas (12 000 K), decrement can change into increment. The HeI λ 5876 flux becomes as large as several percent of the Hα flux only in the hot atmosphere (>15 000 K) or the atmosphere affected by a strong fast particle flux.