2008ApJ...687L..21D

The connection between mass loss on the red giant branch (RGB) and horizontal-branch (HB) morphology in globular clusters (GCs) has long been acknowledged but the mechanisms governing mass loss remain poorly understood from a theoretical perspective. The present study uses synthetic HB models to demonstrate for the first time that α-enhancement and a simple relation between mass loss and metallicity can explain the entire range of HB morphology (characterized by the HB type index) observed in old, coeval GCs. The mass loss-metallicity relation accounts naturally for the fact that the most metal-poor GCs ([Fe/H] < -2) have redder HBs than is typical of GCs with -2 < [Fe/H] < -1.5 without invoking younger ages. These results may prove useful in studying the contribution of HB stars to integrated light via stellar population synthesis.