SYNTHETIC HORIZONTAL-BRANCH MODELS FOR GALACTIC GLOBULAR-CLUSTERS

We present two sets of synthetic horizontal-branch (HB) models which h ave been computed using the evolutionary tracks of Sweigart (1987) (Y( MS) = 0.20, 0.25, 0.30; Z = 10(-4), 10(-3)) and of Lee & Demarque (199 0) (Y(MS) = 0.20, 0.23; 10(-4) less-than-or-equal-to Z less-than-or-eq ual-to 4 10(-3)). Three different values (0.01, 0.02, and 0.03 M.) for the width sigma(M) of the HB mass distribution have been considered f or each of the (Y, Z) combinations that may be obtained for the two em ployed sets of evolutionary tracks. This gives a total of 60 possibili ties which have been analyzed. In each of these cases the mean HB evol utionary mass has been varied so as to yield from very blue to very re d HB morphologies. An extensive tabulation of the morphological and pu lsational results thereby obtained is given for selected cases (Lee & Demarque's tracks, Y(MS) = 0.23). Such models enable a thorough study of some of the properties of the Galactic globular cluster system, inc luding very important issues such as the cluster ages and the long-sta nding Oosterhoff dichotomy and second parameter problems, as well as t he Sandage period-shift effect. According to recent theoretical sugges tions, the enhancement of alpha-elements in halo stars may play a role in what concerns the interpretation of HB properties. In this sense, we make an initial exploration of the present tables, addressing some of the above problems in the light of the adopted theoretical evolutio nary and pulsational frameworks for HB stars and RR Lyrae pulsation.