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

We have obtained new CCD photometry (with short exposures) of the Milky Way globular cluster M 79 using the NTT under excellent seeing(1). The main-sequence turnoff point is at V = 19.70 +/- 0.05, B - V = 0.415 +/- 0.010; the horizontal-branch level at the blue edge of the instability strip is V = 16.25 +/- 0.10. The cluster metallicity, estimated from the positions of the ''bump'' on the red giant branch, is [Fe/H] = -1.76 +/- 0.20. 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 16 +/- 1 Gyr, and in the scale of VandenBerg & Bell (1985) isochrones it is 18 +/- 1 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 (15.(m)6).