OPACITY EFFECTS ON THE RADIATIVE LOSSES OF CORONAL LOOPS

Hydrodynamic flux-tube calculations with energy balance provide us with one of our most basic modeling tools for understanding solar phenomena. These calculations are used for modeling features ranging from quiet-Sun loops to solar flares. A major limitation of these calculations is that they have used the optically thin approximation for calculating radiative energy losses. This assumption is not valid for hydrogen and helium in high-density loops. In this paper we present the results of calculations of radiative losses, which include the effects of geometry and optical depth, that can be used to improve the energy losses in many flux-tube calculations for loops with constant and variable cross sections. The results include the non-LTE ionization state of hydrogen and helium, thus allowing the determination of the ionization energy in the gas and the relative importance of collisional and radiative processes. These calculations show that optical depth effects are important under solar conditions in the temperature range of 8000-40,000 K. These results are presented in a form that can be easily incorporated in hydrodynamic flux-tube calculations.