The Leo IV Dwarf Spheroidal Galaxy: Color-Magnitude Diagram and Pulsating Stars

We present the first V, B - V color-magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B, V time-series photometry reaching about half a magnitude below the Leo IV turnoff, which we detect at V = 24.7 mag, and have performed the first study of the variable star population. We have identified three RR Lyrae stars (all fundamental-mode pulsators, RRab) and one SX Phoenicis variable in the galaxy. In the period-amplitude diagram the Leo IV RR Lyrae stars are located close to the loci of Oosterhoff type I systems and the evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. However, their mean pulsation period, Pab = 0.655 days, would suggest an Oosterhoff type II classification for this galaxy. The RR Lyrae stars trace very well the galaxy's horizontal branch, setting its average magnitude at V RR = 21.48 +/- 0.03 mag (standard deviation of the mean). This leads to a distance modulus of Delta *m0 = 20.94 +/- 0.07 mag, corresponding to a distance of 154 +/- 5 kpc, by adopting for the Leo IV dSph a reddening E(B - V) = 0.04 +/- 0.01 mag and a metallicity of [Fe/H] = -2.31 +/- 0.10.