LUMINOSITY FUNCTIONS FOR POST-TURNOFF STARS IN GLOBULAR-CLUSTERS .1. NGC-288

New BV CCD photometry for the bright stars in the core region of NGC 288, independently calibrated with Landolt [AJ, 88, 439 (1983)] and Graham [PASP, 94, 244 (1982)] standard stars, is presented. In contrast with the color-magnitude diagram of Buonanno et al. [ApJ, 277, 220 (1984)] there are no obvious gaps along the giant branch, but two distinct gaps are evident in the distribution of stars along the horizontal branch-(HB), one near V= 15.7 and one near V = 16.5. The faint blue HB stars defined by the pp at V = 16.5 are pore centrally concentrated than the other HB stars; 80% of them are found within one core radius (1.6') of the cluster center. From HB, isochrone, and luminosity function considerations, the preferred parameters are: Age = 14 Gyr, [Fe/H] = -1.26, (m - M(V)) = 14.90, and E(B-V) = 0.03. Application of the R method calibrated by Caputo et al. [A&A, 183, 228 (1987)] gives a mass fraction helium abundance Y = 0.232(+0.020/-0.036) in excellent agreement with the value (Y = 0.236) adopted by VandenBerg [ApJ, 391, 685 (1992)] for the oxygen-enhanced [Fe/H] = -1.26 evolutionary sequences. Since the age is comparable to that of the extreme metal-poor globular clusters with similar HB morphologies, it is argued that age cannot by itself account for the second parameter effect.