MAIN-SEQUENCE PHOTOMETRY FOR THREE GALACTIC GLOBULAR CLUSTERS.

With the SIT Vidicon camera operated in direct mode at the CTIO 4-m telescope, V,(B-V) color-magnitude data have been obtained for the globular clusters 47 Tuc (NGC 104,C0021-723), NGC 288(C0050-268), and NGC 1904(C0522-245). These data in general cover the V magnitude range from 16 to 22, and accurately define the main sequence turnoff positions for all three clusters. By comparison of our data with the recent theoretical isochrones of VandenBerg (1983), it is found that the main sequence loci of the three clusters can be succesfully matched by ages in the range of 16 + or - 3 billion years, if heavy-element abundances which are similar to spectroscopically derived estimates are adopted.