THE LMB CLUSTER NGC-1841 - PHOTOMETRY OF THE RR LYRAES, AND A COLOR-MAGNITUDE DIAGRAM

B and V CCD photometry of the outlying LMC cluster NGC 1841 has revealed ten new RR Lyrae variables, making a total of 22. The mean period of the 17 RRab stars is 0.676 days; this and other evidence suggest that the metal abundance is very low, [Fe/H] = -2.2 ± 0.2. The mean brightness of the variables is V = 19.31 ± 0.02 (s.e.) and the cluster reddening is E(B - V) = 0.18 ± 0.02. If the RR Lyraes are assumed to have Mυ = 0.5, then NGC 1841 has a distance modulus of 18.19 mag, and is thus some 0.3 mag closer to us than the LMC center. A deep color-magnitude diagram is presented which reaches the main-sequence turnoff at V = 22.6 ± 0.2, confirming that NGC 1841 is as old as galactic globular clusters such as M92.