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A&A Supplement Series, Vol. 125, October I 1997, 1-9

Received July 23, 1996; accepted September 2, 1996

NTT CCD photometry of the globular cluster M 79 = NGC 1904 in UBV

V. Kravtsovtex2html_wrap1244, A. Ipatovtex2html_wrap1246, N. Samustex2html_wrap1246, O. Smirnovtex2html_wrap1246, G. Alcaínotex2html_wrap1252, W. Lillertex2html_wrap1252, and F. Alvaradotex2html_wrap1252

Send offprint request: G. Alcaíno

tex2html_wrap1258  Sternberg Astronomical Institute, Moscow, Russia, and Isaac Newton Institute Moscow Branch, 13, University Ave., Moscow 119899, Russia
tex2html_wrap1260  Institute of Astronomy of Russian Academy of Science, Moscow, Russia, and Isaac Newton Institute Moscow Branch, 48, Pyatnitskaya Str., Moscow 109017, Russia
tex2html_wrap1262  Instituto Isaac Newton, Ministerio de Educacion de Chile, Casilla 8-9, Correo 9, Santiago, Chile


We have obtained new CCD photometry (with short exposures) of the Milky Way globular cluster M 79 using the NTT under excellent seeinggif. The main-sequence turnoff point is at tex2html_wrap_inline1220, tex2html_wrap_inline1222; the horizontal-branch level at the blue edge of the instability strip is tex2html_wrap_inline1224. The cluster metallicity, estimated from the positions of the "bump'' on the red giant branch, is [Fe/H] tex2html_wrap_inline1226. We discuss the luminosity functions of the horizontal branch and the asymptotic giant branch, in particular, the fragmentary structure of the horizontal branch in M 79 and in other clusters. Our isochrone analysis shows that M 79 belongs to the oldest Milky Way globular clusters. Its age, in the scale of Bergbusch & VandenBerg (1992) oxygen-enhanced isochrones, is tex2html_wrap_inline1228 Gyr, and in the scale of VandenBerg & Bell (1985) isochrones it is tex2html_wrap_inline1230 Gyr. The cluster has an extremely blue horizontal branch at intermediate metallicity and may be considered a good example of the "second parameter'' interpreted as age. The apparent distance modulus of the cluster from Bergbusch and VandenBerg isochrones is in good agreement with the value derived from the position of the horizontal branch (tex2html_wrap_inline1232).

keywords: globular clusters: individual: M 79 -- HR diagram

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