The age of old Magelanic Cloud clusters. I: NGC 2257.

Abstract

Deep CCD photometry down to V=24.5 is presented for the old Magellanic Globular cluster NGC 2257. The main result cna be summarized as follows: i) the RGB Bump has been detected at V=18.7+-0.1, and is compatible with determination of this feature in GGCs; ii) NGC 2257 seems to be 2-3 Gyrs younger than a typical GGC; iii) the helium abundance has been estimated to be Y=0.21+-0.03, using the R- method as calibrated by Buzzoni et al., 1983.

10 pages, 9 figures (3 to 9 included), uuencoded tar compressed postscript, 1(splitted) table and figures 1 and 2a,b available upon request