Evidence for an Overluminosity of the Variable Star RR Lyr, and a Revised Distance to the LMC

TL;DR

This paper uses theoretical models and updated measurements to determine that RR Lyrae stars are slightly more luminous than previously thought, leading to a revised distance estimate to the Large Magellanic Cloud.

Contribution

It provides a new relationship between absolute magnitude and metallicity for RR Lyrae stars, accounting for RR Lyr's evolutionary status, and refines the distance to the LMC.

Findings

RR Lyr is overluminosity by 0.064 mag in Stroemgren y.

Revised distance modulus to LMC is 18.44 mag.

New absolute magnitude-metallicity relationship for RR Lyrae stars.

Abstract

We use theoretical models to establish a tight relationship for the absolute magnitudes of RR Lyrae stars as a function of their periods and Stroemgren pseudo-color c_0 = (u-v)_0 - (v-b)_0. Applying this to RR Lyr, and comparing the result with the predicted average absolute magnitude for stars of similar metallicity from the same models, yields an overluminosity of 0.064 +/- 0.013 mag in Stroemgren y (and thus similarly in V) for RR Lyr. Based on a revised value for RR Lyr's trigonometric parallax, and on a newly derived reddening value of E(B-V) = 0.015 +/- 0.020, we provide a corrected relationship between average absolute magnitude and metallicity for RR Lyrae stars that takes RR Lyr's evolutionary status fully into account for the first time. Applying this relationship to the LMC, we derive a revised true distance modulus of (m-M)_0 = 18.44 +/- 0.11.