The Determination Of Reddening From Intrinsic VR Colors Of RR Lyrae Stars

TL;DR

This study assesses the reliability of using minimum light (V-R) colors of RR Lyrae stars to measure interstellar reddening, finding consistent intrinsic colors across different populations and minimal dependence on metallicity or pulsation amplitude.

Contribution

It introduces a new method for determining intrinsic (V-R) colors of RR Lyrae stars at minimum light and compares local and bulge populations for consistency.

Findings

Intrinsic (V-R) color at minimum light is approximately 0.27-0.28 mag.

Minimal dependence of minimum light color on metallicity or pulsation amplitude.

Galactic bulge RR Lyrae colors are similar to local RR Lyrae stars.

Abstract

New R-band observations of 21 local field RR Lyrae variable stars are used to explore the reliability of minimum light (V-R) colors as a tool for measuring interstellar reddening. For each star, R-band intensity mean magnitudes and light amplitudes are presented. Corresponding V-band light curves from the literature are supplemented with the new photometry, and (V-R) colors at minimum light are determined for a subset of these stars as well as for other stars in the literature. Two different definitions of minimum light color are examined, one which uses a Fourier decomposition to the V and R light curves to find (V-R) at minimum V-band light, (V-R)_{min}^F, and the other which uses the average color between the phase interval 0.5-0.8, (V-R)_{min}^{\phi(0.5-0.8)}. From 31 stars with a wide range of metallicities and pulsation periods, the mean dereddened RR Lyrae color at minimum light is (V-R)_{min,0}^F = 0.28 pm 0.02 mag and (V-R)_{min,0}^{\phi(0.5-0.8)} = 0.27 pm 0.02 mag. As was found by Guldenschuh et al. (2005) using (V-I) colors, any dependence of the star's minimum light color on metallicity or pulsation amplitude is too weak to be formally detected. We find that the intrinsic (V-R) of Galactic bulge RR Lyrae stars are similar to those found by their local counterparts and hence that Bulge RR0 Lyrae stars do not have anomalous colors as compared to the local RR Lyrae stars.