THEORETICAL HOT HORIZONTAL-BRANCH STARS

Previous evolutionary computations of horizontal branch stars have bee n extended to the range of ''thin-envelope'', very hot stellar models, in order to make available a homogeneous set of models covering the w hole range of theoretical horizontal branch temperatures. We present e volutionary tracks for selected models of various metallicities, inten ded to represent the theoretical counterpart of hot stars populating e xtremely blue horizontal branches as well as to provide an input for d etailed population synthesis programs devoted to study the origin of t he ultraviolet light in old stellar systems. The role of metallicity i n governing the evolutionary approach to the asymptotic giant branch a nd the contribution of the models to the UV flux are both shortly disc ussed.