Nonequilibrium ionization in solar and stellar winds

Abstract

Substantial and systematic departures from ionization equilibrium can occur in the solar transition region and corona when mass outflows are present. Modeling calculations illustrate the general characteristics of the ionization balance in such regions. The presence of nonequilibrium conditions suggests a natural explanation for the extended region of EUV line emission that is observed above the solar limb. Comparison with observations of a coronal hole on the disk indicates that outflow may not start until temperatures of about 250,000 K are reached. Additional consequences include a diminution of the density discrepancy between ultraviolet and radio observations of coronal holes, and potential effects on the energy balance in solar and stellar atmospheres undergoing mass loss.