HORIZONTAL-BRANCH MORPHOLOGY IN GALACTIC GLOBULAR-CLUSTERS - DENSE ENVIRONMENT IS A 2ND PARAMETER

The Horizontal Branch (HB) morphology in the color-magnitude diagram o f the Galactic globular clusters depends on many factors, and it is no w firmly established that the so-called ''Second Parameter'' is not ju st the cluster age as claimed for several years. As a part of a wider program devoted to the search for the physical processes driving the H orizontal Branch morphology, we re-address here the problem of the ext ension of blue HB tails by introducing a new quantitative observable, B2/B + R + V, where B2 = {Number of HB stars with(B - V)(0) < - 0.02}. We demonstrate that the environmental conditions within a cluster cle arly affect its HE morphology, in the sense that, in general, the high er the cluster central density the higher is the relative number of st ars populating the most blue region of its HB. (C) 1997 American Astro nomical Society.