2004AJ....127.2185N

The physical characteristics of the 10 RR Lyrae stars in the very metal-poor globular cluster NGC 5053 are derived from photometry of ∼1000 B and V CCD frames acquired from 1994 to 2002 with the Dominion Astrophysical Observatory 1.8 m Plaskett Telescope. Revised pulsation periods and light curves, mean magnitudes, colors, amplitudes, and Fourier parameters are presented. Periods accurate to ≲10^–5 days are now known for all 10 RR Lyrae stars. Using times of maximum light dating back to Baade's original 1923-1927 observations, period change rates, dP/dt, accurate to ≲0.07 days/Myr, have been derived for the 10 stars. Seven stars have increasing periods, and three have decreasing periods, with the estimated period change rates for V1, V2, V9, and V10 being very close to zero. The mean dP/dt is equal to 0.04±0.04 days/Myr and is consistent with Lee's evolutionary model predictions for a cluster with horizontal-branch type ∼0.5. Mean B - V colors range from 0.20 to 0.40 and are more consistent with near-zero reddening than alternative higher estimates. A reddening E_B–V=0.018±0.003 is derived from the 1998 SFD maps. Mean effective temperatures vary from 6040 K (V10) to 7290 K (V6), with 2.6≤logg≤3.1. Visual and bolometric absolute magnitudes, bolometric corrections, and luminosities are derived using Fourier methods and using intensity- and magnitude-averaged mean magnitudes. Mean locations of the stars in the H-R diagram tend to progress from hotter, lower L stars to cooler, higher L stars and are consistent with theoretical blue and red edges of the instability strip. Masses estimated assuming zero reddening and Dorman's oxygen-enhanced models range from 0.68 M_☉(V6) to 0.78 M_☉(V10) for the 10 stars. The mean metal abundance for NGC 5053 derived using the Jurcsik-Kovács method lies significantly higher than the range -2.3 to -2.6 dex determined using other, more well established methods. This finding supports recent suggestions that metallicities derived from Fourier-based [Fe/H] calibrations need to be revised downward by at least 0.3 dex for RR Lyrae stars with very low metal abundances.