ABSTRACT
The paper explores the possibility that the forbidden O I 6300-A absorption lines are abnormally weak in the spectra of some brigth globular-cluster giants (like M 13 II67) because they are 'filled in' by forbidden O I emission from an extensive, cool, slowly expanding outer envelope. The results are promising. A very simple one-zone model shows that an H I region with a radius of about 30 AU can provide the supposed emission. The model leads to a mass-loss rate about five times larger than the Reimers 1975 formula predicts and suggests why the average observed value of O/Fe drops near the tip of the giant branch. Absorption in the putative expanding atmosphere qualitatively accounts for the blueshifted Na D line cores that have been observed in the spectra of M 13 II67 and some other bright cluster giants.