Mid-infrared Period-Luminosity Relations of RR Lyrae Stars Derived from the WISE Preliminary Data Release

TL;DR

This study establishes mid-infrared period-luminosity relations for RR Lyrae stars using WISE data, enabling more accurate distance measurements with minimal dust interference and metallicity effects.

Contribution

First to derive mid-infrared PL relations for RR Lyrae stars from phase-resolved WISE data, introducing a novel statistical framework for distance estimation.

Findings

Absolute magnitude in WISE W1 band: -0.421±0.014 - 1.681±0.147*log(P/0.50118 day)

Distance measurement uncertainty: ~1% statistical plus ~1.17% systematic

No evidence of metallicity dependence in the PL relation

Abstract

Interstellar dust presents a significant challenge to extending parallax-determined distances of optically observed pulsational variables to larger volumes. Distance ladder work at mid-infrared wavebands, where dust effects are negligible and metallicity correlations are minimized, have been largely focused on few-epoch Cepheid studies. Here we present the first determination of mid-infrared period-luminosity (PL) relations of RR Lyrae stars from phase-resolved imaging using the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE). We present a novel statistical framework to predict posterior distances of 76 well-observed RR Lyrae that uses the optically constructed prior distance moduli while simultaneously imposing a power-law PL relation to WISE-determined mean magnitudes. We find that the absolute magnitude in the bluest WISE filter is M_W1 = (-0.421+-0.014) - (1.681+-0.147)*log(P/0.50118 day), with no evidence for a correlation with metallicity. Combining the results from the three bluest WISE filters, we find that a typical star in our sample has a distance measurement uncertainty of 0.97% (statistical) plus 1.17% (systematic). We do not fundamentalize the periods of RRc stars to improve their fit to the relations. Taking the Hipparcos-derived mean V-band magnitudes, we use the distance posteriors to determine a new optical metallicity-luminosity relation which we present in Section 5. The results of this analysis will soon be tested by HST parallax measurements and, eventually, with the Gaia astrometric mission.