PULSATING VARIABLE STARS IN THE COMA BERENICES DWARF SPHEROIDAL GALAXY

We present B, V, I time-series photometry of the Coma Berenices dwarf spheroidal galaxy, a faint Milky Way (MW) satellite, recently discovered by the Sloan Digital Sky Survey. We have obtained V, B − V and V, V − I color–magnitude diagrams that reach V ∼ 23.0-23.2 mag showing the galaxy turnoff at V ∼ 21.7 mag, and have performed the first study of the variable star population of this new MW companion. Two RR Lyrae stars (a fundamental-mode, RRab, and a first overtone, RRc, pulsator) and a short period variable with period P = 0.12468 days were identified in the galaxy. The RRab star has a rather long period of Pab = 0.66971 days and is about 0.2 mag brighter than the RRc variable and other nonvariable stars on the galaxy horizontal branch (HB). In the period–amplitude diagram, the RRab variable falls closer to the loci of Oosterhoff type-II systems and evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. The average apparent magnitude of the galaxy HB, 〈VHB〉 = 18.64 ± 0.04 mag, leads to a distance modulus for the Coma dSph μ0 = 18.13 ± 0.08 mag, corresponding to a distance d = 42+2−1 kpc, by adopting a reddening E(B − V) = 0.045 ± 0.015 mag and a metallicity [Fe/H] =−2.53 ± 0.05 dex.