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Astron. Astrophys. 345, 109-116 (1999)


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

Jorick S. Vink 1,2, Sara R. Heap 2, Allen V. Sweigart 2, Thierry Lanz 1,2,3 and Ivan Hubeny 2

1 Astronomical Institute (University of Utrecht), Princetonplein 5, 3584 CA Utrecht, The Netherlands
2 Laboratory for Astronomy and Solar Physics, Code 681, Goddard Space Flight Center, Greenbelt, MD 20771, USA
3 Department of Astronomy, University of Maryland, College Park, MD 20742, USA

Received 4 January 1999 / Accepted 5 February 1999

Abstract

We have analyzed the far UV-spectrum of the globular cluster M79. We show that the nearly Gaussian mass distribution of zero-age horizontal-branch stars, as derived by Dixon et al. (1996), is able to reproduce the far-UV Hopkins Utraviolet Telescope (HUT) spectrum, if there is a luminous UV-bright star of about [FORMULA] = 9,500 K within the HUT entrance slit, or, more likely, if the horizontal branch morphology becomes considerably redder in the core of M79, as observed in some other centrally condensed globular clusters. Agreement between the synthetic and observed far-UV spectra for M79 would also be improved if the surface abundances of the heavy elements in the hot horizontal-branch stars were enhanced by radiative diffusion. Contrary to Dixon et al. (1996) we do not need extremely low gravities to reproduce the width of Ly [FORMULA].

Key words: ultraviolet: stars – ultraviolet: general – stars: evolution – stars: Hertzsprung – Russel (HR) and C-M diagrams – stars: horizontal-branch – Galaxy: globular clusters: individual: M79

Send offprint requests to: Jorick S. Vink (j.s.vink@astro.uu.nl)

© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999

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