Observations of red variable stars in globular clusters

Extensive observations of line strengths in the spectra of variable and constant stars in globular clusters show that while variable stars often have H emission lines, the H lines in variables of small amplitude often show stronger absorption than typical non-variable stars. Strong H emission is found in stars of smaller amplitude as well as in Mira variables, especially in the more metal-deficient clusters, and is often accompanied by a weakening of strong lines of neutral metals which is well known in Mira variables. The subdivision of red variables into Mira, semi-regular and supragiant branch stars, as well as small amplitude variables on the giant branch, is apparent in 47 Tuc: the extension of this subdivision to very metal-poor clusters, where generally small amplitudes and a prevalence of strong H emission complicate the situation, is discussed. A newly discovered variable in NGC 362 has a period of 135 days. (author)