The Effects of Electron and Radiation Density on Dielectronic Recombination

Abstract

The statistical-equilibrium populations of excited states of He, O÷~, O~, Ca, Fe+7 and Fe+14 for a wide range of electron density and temperature have been calculated, including the effects of dielec- tronic recombination as well as radiative and three-body recombination, together with collisional and radiative transitions between all states We define, and results are given for, the corresponding overall recombination coefficient, for which we propose the name coiis~ona1-die1eciromic recombination coefficient. Oxygen-ion abundance curves are given for a wide range of electron densities. They show that density effects are not very important in the outer corona, but may be appreciable in the inner corona and the chromosphere The excited-state popu'ations are much more strongly affected by the electron density. Very strong population inversions can arise, but Doppler shifts due to thermal motions seem to be too large for lasing to occur in the corona. This may not be the case for more massive high-temperature, low-density objects The effects of the photospheric radiation field on coronal ions are calculated, with all transitions induced by this field taken into account In contradiction to some earlier approximate calculations, these effects are shown to be relatively small The form of variation of the collisional- dielectronic recombination coefficient with density and temperature can in some cases produce a tendency toward thermal instability