SIMBAD references

Radiative heating and cooling in the circumstellar envelopes of cool stars is investigated, considering gas densities of 10^4...14cm^–3 and gas temperatures of 500...20000K. Various heating and cooling processes are included: rotational and ro-vibrational transitions of polar molecules and of H₂, atomic line transitions, bound-free transitions, free-free transitions and photochemical reactions. Theoretical concepts and computational methods are worked out, which on the one hand can account for important non-LTE effects and radiative trapping and on the other hand allow for a fast and proper inclusion of these heating and cooling rates into time-dependent hydrodynamical model calculations. Radiative cooling timescales for a carbon-enriched gas typical for C-star atmospheres are calculated, and the thermal relaxation of the gas after the passage of shock waves is discussed. A gradual transition of the character of the propagating shock waves is expected to occur at densities around 10^6...8cm^–3, changing from predominantly isothermal to predominantly adiabatic with decreasing gas density.