Long Period Variables in Globular Clusters and the Galactic Bulge: Their Dependence on Metallicity

Abstract

We derive the frequency of occurrence of luminous long period variables (LLPVs) in globular clusters and in the Baade's Window field of the Galactic bulge. LLPVs occur only in clusters with [Fe/H]>/= -1.0. In these clusters their frequency of occurrence relative to the number of giant stars appears to be independent of metallicity. Integrated over all metallicities, Baade's Window appears to be deficient in LLPVs. We estimate [Fe/H] values for Baade's Window LLPVs from their period and a log P vs. [Fe/H] relation derived from cluster variables and find that LLPVs with [Fe/H]>/= 0.0 are absent from Baade's Window. We propose that this is because of enhanced mass loss rates in these LLPVs with a consequently abbreviated lifetime compared to lower metallicity LLPVs. A typical lifetime for cluster LLPVs is about 3 x10^5 yrs. Finally, we call attention to the need for a much more complete survey for LLPVs in globular clusters.