VARIABLE STARS IN THE FORNAX dSph GALAXY. III. THE GLOBULAR CLUSTER FORNAX 5

We present a new study of the variable star population in globular cluster 5 of the Fornax dSph, based on B and V time series photometry obtained with the MagIC camera of the 6.5 m Magellan Clay telescope and complementary Hubble Space Telescope archive data. Light curves and accurate periodicities were obtained for 30 RR Lyrae stars and one SX Phoenicis variable. The RR Lyrae sample includes 15 fundamental-mode pulsators, 13 first-overtone pulsators, one candidate double-mode pulsator and one RR Lyrae star with uncertain type classification. The average and minimum periods of the ab-type RR Lyrae stars, 〈Pab〉 = 0.590 days, Pab,min = 0.53297 days and the position in the horizontal branch type–metallicity plane, indicate that the cluster has Oosterhoff-intermediate properties, basically confirming previous indications by Mackey & Gilmore, although with some differences both in the period and type classification of individual variables. The average apparent magnitude of the Fornax 5 RR Lyrae stars is 〈V(RR)〉 = 21.35 ± 0.02 mag (σ = 0.07 mag, average on 14 stars more likely belonging to the cluster, and having well sampled light curves). This value leads to a true distance modulus of μ0 = 20.76 ± 0.07 (d = 141.9+4.6−4.5 kpc) if we adopt for the cluster the metal abundance by Buonanno et al. ([Fe/H] = −2.20 ± 0.20), or μ0 = 20.66 ± 0.07 (d = 135.5+4.4−4.3 kpc), if we adopt Strader et al.'s metal abundance ([Fe/H] = −1.73 ± 0.13).