Radiative equilibrium in solar prominences reconsidered

Abstract

Aims: We reconsider the question which kinetic temperatures can lead to prominence configurations that are in radiative equilibrium. We compare these temperatures to those from other calculations.
Methods: For this purpose we solved the full non-LTE radiative-transfer problem for a gas consisting of hydrogen, helium and calcium. We used simple isobaric 1D slabs and began with isothermal models. Then we solved the radiative-relaxation problem and determined the radiative-equilibrium conditions within the whole slab.
Results: By adding the calcium radiative losses, we found that these equilibrium temperatures are considerably lower than those obtained for a pure hydrogen gas. This is because the newly calculated CaII line losses appear to play a significant role in the energy balance, similar to chromospheric conditions. The equilibrium temperatures obtained span the range between 4400-9500 K, depending on the gas pressure and slab thickness.