Hot stellar population synthesis from the UV spectrum: the globular cluster M79 (NGC 1904)

We have analyzed the far UV-spectrum of the globular cluster M79. We show t hat the nearly Gaussian mass distribution of zero-age horizontal-branch sta rs, as derived by Dixon et al. (1996), is able to reproduce the far-UV Hopk ins Utraviolet Telescope (HUT) spectrum, if there is a luminous UV-bright s tar of about T-eff = 9,500 K within the HUT entrance slit, or, more likely, if the horizontal branch morphology becomes considerably redder in the cor e of M79, as observed in some other centrally condensed globular clusters. Agreement between the synthetic and observed far-UV spectra for M79 would a lso be improved if the surface abundances of the heavy elements in the hot horizontal-branch stars were enhanced by radiative diffusion. Contrary to D ixon et al. (1996) we do not need extremely low gravities to reproduce the width of Ly alpha.