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.

On the formation of Mg ii h and k lines in solar prominences

“…For all nine models, we start from a uniform temperature of 10 000 K, and let the prominence slab relax to RE. Resulting RE temperatures at the slab center and surface are summarized in Table 3, which is similar to that in Heinzel & Anzer (2012). We also compare our new results with the pure hydrogen case and hydrogen-calcium mixture.…”

“…The effect is rather marginal for the highest gas pressure 0.5 dyne cm −2 but increases substantially toward low pressures. For p = 0.01 dyne cm −2 , the effect of Mg ii lines is quite large and much more important than that of Ca ii found earlier in Heinzel & Anzer (2012). This behavior can be explained by the much larger opacity of Mg ii lines in prominence slabs as compared to Ca ii lines.…”

“…We also compare our new results with the pure hydrogen case and hydrogen-calcium mixture. In the latter case, we have updated our previous Ca ii modeling, and thus, small differences appear in the present table as compared to that in Heinzel & Anzer (2012).…”

“…For a more recent modeling see Carlsson & Leenaarts (2012). Therefore, Mg ii contributes by less than 25% to these losses and, therefore, we have neglected them in our recent radiation-equilibrium (RE) models of 1D prominence slabs (Heinzel & Anzer 2012). These RE models, which include Ca ii losses, exhibit a substantial decrease of the radiationequilibrium temperatures in 1D slabs as compared to the pure hydrogen case previously studied by Gouttebroze (2007).…”

“…In Sect. 6, we construct the thermal models in radiative equilibrium by adding the magnesium radiative losses to those previously considered by Heinzel & Anzer (2012). Section 7 contains Discussion and Conclusions.…”