RR Lyrae Stars in the Boötes Dwarf Spheroidal Galaxy

Abstract

We present a catalog of 15 RR Lyrae variable stars in the recently discovered Bootes galaxy -- the most metal-poor simple stellar population with measured RR Lyrae stars. The pulsational properties of the RR Lyrae conform closely to period-abundance trends extrapolated from more metal-rich populations and we estimate the distance of Bootes to be (m-M)_0=18.96+-0.12. The average period (0.69 days), the ratio of type c to type ab pulsators (0.53) and the RRab period shift (-0.07) indicate an Oosterhoff II classification for Bootes, a marked contrast to the other dSph galaxies, which are Oosterhoff intermediate. This supports the contention that the Oosterhoff dichotomy is a continuum -- that RR Lyrae properties, to first order, vary smoothly with abundance. The dSph galaxies are not distinct from the Galactic globular clusters, but bridge the Oosterhoff gap. The absence of any anomalous Cepheids in Bootes could indicate the lack of an intermediate age population.