# Characterization of the VVV Survey RR Lyrae Population across the Southern Galactic Plane

## TL;DR

This study identifies and characterizes 404 RR Lyrae stars in the Southern Galactic plane using deep near-IR imaging from the VVV Survey, revealing their distribution and potential for Galactic evolution insights.

## Contribution

The paper provides the first large sample of RR Lyrae stars in this region, highlighting their spatial distribution and relation to Galactic structures, with implications for future Gaia observations.

## Key findings

- RR Lyrae stars are concentrated near the bulge tangent point.
- The population is mainly Oosterhoff type I and does not trace the Galactic bar.
- Half of the RR Lyrae are accessible to Gaia for detailed astrometric studies.

## Abstract

Deep near-IR images from the VISTA Variables in the V\'ia L\'actea (VVV) Survey were used to search for RR Lyrae stars in the Southern Galactic plane. A sizable sample of 404 RR Lyrae of type ab stars was identified across a thin slice of the 4$^{\rm th}$ Galactic quadrant ($295\deg < l < 350\deg$, $-2.24\deg < b < -1.05\deg$). The sample's distance distribution exhibits a maximum density that occurs at the bulge tangent point, which implies that this primarily Oosterhoff type I population of RRab stars does not trace the bar delineated by their red clump counterparts. The bulge RR Lyrae population does not extend beyond $l \sim340 \deg$, and the sample's spatial distribution presents evidence of density enhancements and substructure that warrants further investigation. Indeed, the sample may be employed to evaluate Galactic evolution models, and is particularly lucrative since half of the discovered RR Lyrae are within reach of Gaia astrometric observations.