Abstract

"We present results of a project devoted to the extensive survey of the ultra-faint Milky Way dwarf spheroidal satellites recently discovered by the SDSS (Bootes I, Ursa Major II, Coma, Hercules, Canes Venatici I, Canes Venatici II, Leo IV), that we are monitoring for variability using time-series multiband observations collected at a variety of telescopes from the 1.5 to the 4.3 m size, and reaching each galaxy's main sequence tumoff. In particular, we present results on the pulsation properties and ""Oosterhoff type"" of the RR Lyrae stars detected in two of the newly discovered dwarf spheroidals, namely Leo IV and Ursa Major II. The variable stars and the stellar populations of these two galaxies are discussed in light of the insight they can provide to reconstruct the star formation history and the merging episodes that led to the early assembly of the Galactic halo. © 2009 American Institute of Physics."