RR Lyrae and Type II Cepheid Variables Adhere to a Common Distance Relation

Volume 38 number 1 (2010)

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Danial J. Majaess

Abstract

Preliminary evidence is presented reaffirming that SX Phe, RR Lyrae, and Type II Cepheid variables may be characterized by a common Wesenheit period-magnitude relation, to first order. Reliable distance estimates to RR Lyrae variables and Type II Cepheids are ascertained from a single VI-based reddeningfree relation derived recently from OGLE photometry of LMC Type II Cepheids. Distances are computed to RR Lyrae (d ~ = 260 pc) and variables of its class in the galaxies IC 1613, M33, Fornax dSph, LMC, SMC, and the globular clusters M3, M15, M54, w Cen, NGC 6441, and M92. The results are consistent with literature estimates, and in the particular cases of the SMC, M33, and IC 1613, the distances agree with those inferred from classical Cepheids to within the uncertainties: no corrections were applied to account for differences in metallicity. Moreover, no significant correlation was observed between the distances computed to RR Lyrae variables in w Cen and their metallicity, despite a considerable spread in abundance across the sample. In sum, concerns regarding a sizeable metallicity effect are allayed when employing VI-based reddening-free Cepheid and RR Lyrae relations.