Discovery of $\sim$ 9,000 new RR Lyrae in the Southern Catalina Surveys

TL;DR

This study identified approximately 9,000 new RR Lyrae stars in the Southern sky using a novel survey and algorithms, providing insights into their metallicity distribution, spatial gradients, and associated galactic substructures.

Contribution

The paper introduces two new algorithms for efficient period and lightcurve analysis, leading to the discovery of a large sample of RR Lyrae stars and initial substructure identification.

Findings

Discovered ~9,000 new RR Lyrae stars in the Southern hemisphere.

Found a Gaussian metallicity distribution with mean [Fe/H] = -1.4 dex.

Identified a southern extension of the Sagittarius stream.

Abstract

We present the results of a deep, wide-area variability survey in the Southern hemisphere, the first of its kind. As part of the Catalina Sky Surveys, the Siding Spring Survey (SSS) has covered $14,800$ square degrees in the declination range of $-75^{\circ}\leq\delta\leq-15^{\circ}$. To mine the enormous SSS dataset efficiently we have developed two algorithms: Automatic Period Selection (APS) and Automatic Fourier Decomposition (AFD), which aim to sharpen the period estimation and produce robust lightcurve models. Armed with the APS and AFD outputs we classify $10,540$ ab-type RR Lyrae (RRab) stars ($\sim$90% of which are new) across the Southern sky. As well as the positional information we supply photometric metallicities, and unreddened distances. For the RRab stars in the halo, a study of the photometric metallicity distribution reveals a nearly Gaussian shape with a mean metallicity of ${\rm [Fe/H]}=-1.4$ dex and a dispersion of $0.3$ dex. A spatial study of the RRab metallicities shows no significant radial gradient in the first $\sim7$ kpc from the Galaxy center. However, further out, a small negative gradient is clearly present. This is complemented by a very obvious correlation of the mean RR Lyrae metallicity with distance above the Galactic plane, $z$. We have also carried out an initial substructure search using the discovered RRab, and present the properties of the candidates with significance greater than $2 \sigma$. Most prominent among these is a southern extension of the Sagittarius dwarf galaxy's stream system, reaching down to declinations $\sim -40\deg$.