Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey

TL;DR

This study analyzes 838 RR Lyrae stars from the LONEOS-I survey to investigate the structure and components of the Galactic stellar halo, revealing evidence for at least two distinct halo populations formed by different accretion events.

Contribution

The paper provides a large, detailed sample of RR Lyrae stars to distinguish between different halo components and their formation histories.

Findings

Majority of RR Lyrae stars are Oosterhoff type I.

Significant fraction (26%) are Oosterhoff type II.

Different radial density profiles support dual-halo formation models.

Abstract

We present 838 ab-type RR Lyrae stars from the Lowell Observatory Near Earth Objects Survey Phase I (LONEOS-I). These objects cover 1430 deg^2 and span distances ranging from 3-30 kpc from the Galactic Center. Object selection is based on phased, photometric 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 these RR Lyrae stars 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 radial distributions of these two populations have significantly different profiles (rho_{OoI} ~ R^(-2.26 +- 0.07) and rho_{OoII} ~ R^(-2.88 +- 0.11). This suggests that the stellar halo was formed by at least two distinct accretion processes and supports dual-halo models.