Gaia RR Lyrae Stars in Nearby Ultra-faint Dwarf Satellite Galaxies

Abstract

We search for RR Lyrae stars (RRLs) in 27 nearby (<100 kpc) ultra-faint dwarf satellite galaxies using the Gaia DR2 catalog of RRLs. Based on proper motions, magnitudes, and location on the sky, we associate 47 Gaia RRLs with 14 different satellites. Distances based on RRLs are provided for those galaxies. We have identified RRLs for the first time in the Tucana II dwarf galaxy, and find additional members in Ursa Major II, Coma Berenices, Hydrus I, Bootes I, and Bootes III. In addition we have identified candidate extra-tidal RRLs in six galaxies, which suggests they may be undergoing tidal disruption. We found 10 galaxies have no RRLs either in Gaia or in the literature. However, given the known completeness of Gaia DR2 we cannot conclude these galaxies indeed lack variable stars of this type.