Colors of c-type RR Lyrae Stars and Interstellar Reddening

TL;DR

This study investigates the color properties of first overtone RR Lyrae stars (RRc) and their potential as indicators of interstellar reddening, expanding the traditional use of fundamental mode RR Lyrae stars.

Contribution

It provides new V-I color observations of RRc stars and analyzes their period-color relation, highlighting their independence from metallicity and usefulness in reddening estimation.

Findings

RRc colors correlate with period but not metallicity.

RRc stars show slightly more scatter in period-color relation than RRab.

RRc stars can serve as reddening indicators in old stellar systems.

Abstract

RR Lyrae stars pulsating in the fundamental mode have long been used to measure interstellar reddening, based on their observed uniformity of $B-V$ color at minimum light after small corrections for metallicity and period are applied. However, little attention has been paid to the first overtone pulsators (RRc or RR1). We present new $V-I$ observations of field RRc stars, supplemented with published data from uncrowded RRc in globular clusters. Preliminary results indicate the RRc colors are correlated with period, but appear to be independent of the stars' metallicity. The scatter around the period-color relation is slightly larger than a comparable relation for RRab. Thus, RRc can be useful indicators of line of sight reddening toward old stellar systems, particularly when multiple stars are available as in Oosterhoff II globular clusters and metal-poor galaxies.