Ultraviolet Fe ii emission in late-type stars

Spectrograms of 44 K and M giants and supergiants have been taken with the Cassegrain and coude spectrographs of the Mauna Kea 224 cm telescope to determine the presence and intensity of the ultraviolet emission lines of Fe ii from multiplets 1,6, and 7. The emission is nearly universal in the M stars, but not found in any of the K stars; it thus appears to be a natural consequence of stellar surface temperature. The intensity of the emission is well correlated with the strengths of the circumstellar components of the K-line of Ca ii and of Hα. It is suggested that the emission arises in the circumstellar gas shell and that its intensity is a primary indicator of the extent of the shell. There is no apparent relationship between the Fe ii emission intensity and the amount of infrared excess at 11 and 20 μ, the indicators of a circumstellar dust shell