NTT CCD PHOTOMETRY OF THE GLOBULAR-CLUSTER M-79 = NGC-1904 IN UBV

We have obtained new CCD photometry (with short exposures) of the Milk y Way globular cluster M 79 using the NTT under excellent seeing(1). T he 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 instab ility 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 horizonta l branch and the asymptotic giant branch, in particular, the fragmenta ry structure of the horizontal branch in M 79 and in other clusters. O ur isochrone analysis shows that M 79 belongs to the oldest Milky Way globular clusters. Its age, in the scale of Bergbusch & VandenBerg (19 92) oxygen-enhanced isochrones, is 16 +/- 1 Gyr, and in the scale of V andenBerg & Bell (1985) isochrones it is 18 +/- 1 Gyr. The cluster has an extremely blue horizontal branch at intermediate metallicity and m ay be considered a good example of the ''second parameter'' interprete d 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).