LONEOS RR Lyrae stars as probes of galactic structure and formation

We present 789 ab-type RR Lyrae from the Lowell Observatory Near Earth Objects Survey (LONEOS). These objects cover 1430 deg 2 and span distances ranging from 3-30kpc from the Galactic Center. Object selection is based on phased, temporal data with 28-50 epochs. We use this large sample to explore the bulk properties of the stellar halo, including the spatial distribution. The period-amplitude distribution of this sample shows that the majority of the RR Lyrae resemble Oosterhoff type I, but there is a significant fraction (26%) which have longer periods and appear to be Oosterhoff type II. We find that the spatial distributions of these two populations have significantly different radial profiles (rhoOoI ∼ R -2.33+/-0.1 and rhoOoI I ∼ R-2.94+/-0.04 ). This suggests that the stellar halo was formed by at least two distinct physical processes and supports dual-halo models.