MULTICOLOR CCD PHOTOMETRY OF THE POORLY STUDIED GLOBULAR-CLUSTER NGC-6541

We have carried out the first accurate multicolor (UBVRI) CCD photomet ry for more than 3000 stars (12.(m)3<V<21.(m)0) in the field of the gl obular cluster NGC 6541, This cluster was neglected in photometric stu dies after two photographic investigations by Alcaino (1971, A&A, 13, 399; 1979, A&AS, 35, 233). The color-magnitude diagrams show close mor phological similarities with M13 and M79, with the horizontal branch e xtending over 3 mag in V. We find the main-sequence turnoff at V-TO=-1 8.9+/-0.1. The V magnitude difference between the main sequence turnof f and the horizontal branch may be as great as 3.(m)7. Four probable b lue stragglers have been found. Comparing the cluster's CMD with that for the well-studied and little reddened cluster M79, we derive the es timates of metallicity ([Fe/H]approximate to-1.8+/-0.2) and of reddeni ng (E(B-V)=0.15+/-0.02), We note considerable discrepancy in the posit ions of the horizontal branch in NCC 6541 and M79 in the U-(B-V) diagr am and in the (U-B)-(B-V) two-color diagram. Our comparison of the col or-magnitude diagrams with oxygen-enhanced isochrones shows that the c luster is very old; its age is at least 16 to 17 Gyr from the V-(B-V) diagram and perhaps older according to the other of our color-magnitud e diagrams, (We assume here and for now no downward adjustments of age based on recent HIPPARCOS data) (C) 1997 American Astronomical Societ y.