  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 remains poorly understood from a
theoretical perspective. The present study uses synthetic HB models to
demonstrate for the first time that alpha-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.
