A rich harvest of RR Lyrae stars has been identified for the first time in B514, a metal-poor ([Fe/H] = 1.95 +/- 0.10 dex) globular cluster of the Andromeda galaxy (M31), based on Hubble Space Telescope Wide Field Planetary Camera 2 and Advanced Came
ra for Surveys time-series observations. We have detected and derived periods for 89 RR Lyrae stars (82 fundamental-mode -RRab- and 7 first-overtone -RRc- pulsators, respectively) among 161 candidate variables identified in the cluster. The average period of the RR Lyrae variables (<Pab> = 0.58 days and <Pc> = 0.35 days, for RRab and RRc pulsators, respectively) and the position in the period-amplitude diagram both suggest that B514 is likely an Oosterhoff type I cluster. This appears to be in disagreement with the general behaviour of the metal-poor globular clusters in the Milky Way, which show instead Oosterhoff type II pulsation properties. The average apparent magnitude of the RR Lyrae stars sets the mean level of the cluster horizontal branch at <V(RR)> = 25.18 +/- 0.02 (sigma=0.16 mag, on 81 stars). By adopting a reddening E(B-V) = 0.07 +/- 0.02 mag, the above metallicity and M_V=0.44 +/- 0.05 mag for the RR Lyrae variables of this metallicity, we derive a distance modulus of mu_0=24.52 +/- 0.08 mag, corresponding to a distance of about 800 +/- 30 kpc, based on a value of M_V that sets mu_0(LMC)=18.52.
We present a new study of the variable star population in globular cluster 5 of the Fornax dwarf spheroidal galaxy, based on B and V time series photometry obtained with the MagIC camera of the 6.5 m Magellan Clay telescope and complementary HST arch
ive data. Light curves and accurate periodicities were obtained for 30 RR Lyrae stars and 1 SX Phoenicis variable. The RR Lyrae sample includes 15 fundamental-mode pulsators, 13 first-overtone pulsators, 1 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, P(ab,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 (2003b), 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 (sigma=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 mu0=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. (1998; [Fe/H]=-2.20 +/- 0.20), or mu0=20.66 +/- 0.07 (d=135.5 (+4.4;-4.3) kpc), if we adopt Strader et al.s (2003) metal abundance ([Fe/H]=-1.73 +/- 0.13).
We report on the detection of variable stars in the Canes Venatici II (CVn II) dwarf spheroidal galaxy, a new satellite of the Milky Way recently discovered by the Sloan Digital Sky Survey. We also present a V, B-V color-magnitude diagram that reache
s V = 25.5 mag, showing the galaxys main sequence turn off at V = 24.5 mag and revealing several candidate blue straggler stars. Two RR Lyrae stars have been identified within the half-light radius of CVn II,a fundamental-mode variable (RRab) with period P_ab = 0.743 days, and a first-overtone (RRc) RR Lyrae star with P_c = 0.358 days. The rather long periods of these variables along with their position on the period-amplitude diagram support an Oosterhoff type II classification for CVn II. The average apparent magnitude of the RR Lyrae stars, <V> = 21.48 +/- 0.02 mag, is used to obtain a precision distance modulus of mu_0 = 21.02 +/- 0.06 mag and a corresponding distance of 160(+4,-5} kpc, for an adopted reddening E(B-V) = 0.015 mag.
We present a new, deep (V ~ 26) study of the Galactic globular cluster NGC 2419 based on B,V,I time-series CCD photometry over about 10 years and extending beyond the cluster published tidal radius. We have identified 101 variable stars of which 60 a
re new discoveries, doubling the known RR Lyrae stars and including 12 SX Phoenicis stars. The average period of the RR Lyrae stars (<Pab>=0.662 d, and <Pc>=0.366 d, for fundamental-mode -RRab- and first-overtone pulsators, respectively), and the position in the period-amplitude diagram both confirm that NGC 2419 is an Oosterhoff II cluster. The average apparent magnitude of the RR Lyrae stars is <V>=20.31 +/- 0.01 (sigma=0.06, 67 stars) and leads to the distance modulus (m-M)o=19.60 +/- 0.05. The Color-Magnitude Diagram, reaching about 2.6 mag below the cluster turn-off, does not show clear evidence of multiple stellar populations. Cluster stars are found until r~ 10.5, and possibly as far as r~15, suggesting that the literature tidal radius might be underestimated. No extra-tidal structures are clearly detected in the data. NGC 2419 has many blue stragglers and a well populated horizontal branch extending from the RR Lyrae stars down to an extremely blue tail ending with the blue-hook, for the first time recognized in this cluster. The red giant branch is narrow ruling out significant metallicity spreads. Our results seem to disfavor the interpretation of NGC 2419 as either having an extragalactic origin or being the relict of a dwarf galaxy tidally disrupted by the Milky Way.
Variable stars have been identified for the first time in Fornax 4, the globular cluster located near the center of the Fornax dwarf spheroidal galaxy. By applying the image subtraction technique to B,V time series photometry obtained with the MagIC
camera of the 6.5-m Magellan/Clay telescope and with the wide field imager of the 4-m Blanco/CTIO telescope, we detected 27 RR Lyrae stars (22 fundamental mode, 3 first overtone, and 2 double-mode pulsators) in a 2.4x2.4 area centered on Fornax 4. The average and minimum periods of the ab-type RR Lyrae stars, <Pab>= 0.594 d and P(ab,min)=0.5191 d, respectively, as well as the revised position of the cluster in the horizontal branch type--metallicity plane, all consistently point to an Oosterhoff-intermediate status for the cluster, unlike what is seen for the vast majority of Galactic globular clusters, but in agreement with previous indications for the other globular clusters in Fornax. The average apparent magnitude of the RR Lyrae stars located within 30 arcsec from the cluster center is <V(RR)>=21.43 +/- 0.03 mag (sigma=0.10 mag, average on 12 stars), leading to a true distance modulus of (m-M)o=20.64 +/- 0.09 mag or (m-M)o=20.53 +/- 0.09 mag, depending on whether a low ([Fe/H]=-2.0) or a moderately high ([Fe/H]=-1.5) metallicity is adopted.
