BV photometry of RR Lyrae variables in the globular cluster NGC 3201

Abstract

BV photometry is presented for 48 ab-type and 4 c-type RR Lyrae variables in the globular cluster NGC 3201. The analysis of the reddening across the cluster reveals an irregular distribution with ..delta..E(B-V) = 0.02 to 0.03 mag. The adopted mean value is E(B-V) = 0.21 +- 0.03 mag. A significant larger value of the reddening, as suggested by a number of independent estimations, would result in a discrepancy between the data and the theoretical stellar models. The comparison of the light curve parameters (periods, amplitudes, colors, rise times) for the variables in NGC 3201 and M3 reconfirms the already known strong similarity of the two clusters. The metal abundance (Fe/H) = -1.4 has been assumed as the most consistent value with the general properties of the cluster. The implications of a larger value of metal abundance, as it is found by high-dispersion spectroscopy of single red giants, are discussed. The helium content has been estimated with different methods, and the value Y = 0.24 +- 0.03 has been adopted. Using the pulsation theory the mass-luminosity relation log L = 1.83 +- 0.81 log M has been derived, which leads to the absolute magnitude for the RR Lyrae stars M/submore » v/ (RR) = 0.60 +- 0.08 mag on the assumption that their mass is M = 0.65 M/sub sun/. The age of the cluster has been calculated comparing the derived turn-off luminosity with the results of evolution theory, and is t(9) = 12 +- 3 yr with no indication of it being much different for M3.« less