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 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
Milky Way 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
non-variable stars on the galaxy horizontal branch. 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 horizontal branch,
<V_HB>=18.64+-0.04 mag, leads to a distance modulus for the Coma dSph
mu_0=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.
