The Galactic globular cluster system - Theoretical constraints for alpha-enhanced compositions

Synthetic horizontal branches are constructed from a grid of horizontal-branch (HB) evolutionary tracks with the α-elements (O, Ne, Mg, and Ca) enhanced by a factor of 5 with respect to the solar-scaled mixture and various surface helium and heavy-element abundances. The relevant constraints on HB morphology and mean properties of RR Lyrae variables are presented and discussed.