RR LYRAE STARS IN THE BOOETES DWARF SPHEROIDAL GALAXY

摘要

We present a catalog of 15 RR Lyrae variable stars in the recently discovered Booetes dwarf spheroidal (dSph) galaxy-the most metal-poor 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. We estimate the distance of Booetes to be (m - M)_0 = 18.96 ± 0.12. The average RRab period (0.69 days), the fraction of type c pulsators (0.53), and the RRab period shift (-0.07) indicate an Oosterhoff type Ⅱ classification for Booetes, a marked contrast to other dSph galaxies, which are mostly 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 Galactic globular clusters but bridge the Oosterhoff gap. In contrast to other dSph galaxies, Booetes lacks any anomalous Cepheids.