Fe - MG II K line fluorescence in K giant and bright giant stars.

Abstract

Emission lines of Fe I from the multiplet uv44 are observed at 2823.28A and 2843.98A in late-type giant and bright giant stars. It has been recognized for some time that these lines can be excited by Mg II k line radiation in the transition at 2795.54A. The first radiative transfer calculations to account for the strength of the Fe I lines Iota Aur (K3 II), Alpha Boo (K2 III), Beta Gem (K0 III) and Alpha Tau (K5 III) show that the observed Fe I is created in the chromospheres of the K stars and not in circumstellar shells, as suggested by some authors. The Fe I lines provide an additional test of model chromospheres at temperatures between those where the Mg II and Ca II resonance lines are formed.