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 , \langle P { ab } \rangle =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 \langle V _ { RR } \rangle = 21.48 \pm 0.03 mag ( standard deviation of the mean ) .
This leads to a distance modulus of \mu _ { 0 } = 20.94 \pm 0.07 mag , corresponding to a distance of 154 \pm 5 kpc , by adopting for the Leo IV dSph a reddening E ( B - V ) = 0.04 \pm 0.01 mag and a metallicity of [ Fe/H ] = -2.31 \pm 0.10 .