2009ApJ...695L..83M

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 P_ab= 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, HB> = 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_–1kpc, by adopting a reddening E(B - V) = 0.045 ± 0.015 mag and a metallicity [Fe/H] =-2.53±0.05 dex.