RR Lyrae Mid-infrared Period–Luminosity–Metallicity and Period–Wesenheit–Metallicity Relations Based on Gaia DR3 Parallaxes

Abstract

We present new empirical infrared period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations for RR Lyae based on the latest Gaia Early Data Release 3 (EDR3) parallaxes. The relations are provided in the Wide-field Infrared Survey Explorer (WISE) W1 and W2 bands, as well as in the W(W1, V − W1) and W(W2, V − W2) Wesenheit magnitudes. The relations are calibrated using a very large sample of Galactic halo field RR Lyrae stars with homogeneous spectroscopic [Fe/H] abundances (over 1000 stars in the W1 band), covering a broad range of metallicities (−2.5 ≲ [Fe/H] ≲ 0.0). We test the performance of our PLZ and PWZ relations by determining the distance moduli of both galactic and extragalactic stellar associations: the Sculptor dwarf spheroidal galaxy in the Local Group (finding μ ¯ 0 = 19.47 ± 0.06 ), the Galactic globular clusters M4 ( μ ¯ 0 = 11.16 ± 0.05 ), and the Reticulum globular cluster in the Large Magellanic Cloud ( μ ¯ 0 = 18.23 ± 0.06 ). The distance moduli determined through all our relations are internally self-consistent (within ≲0.05 mag) but are systematically smaller (by ∼2–3σ) than previous literature measurements taken from a variety of methods/anchors. However, a comparison with similar recent RR Lyrae empirical relations anchored with EDR3 likewise shows, to varying extents, a systematically smaller distance modulus for PLZ/PWZ RR Lyrae relations.

New Near-infrared Period–Luminosity–Metallicity Relations for Galactic RR Lyrae Stars Based on Gaia EDR3 Parallaxes

“…However, we observe a strong correlation between the period and metallicity slopes. Such a correlation was reported recently by Mullen et al (2023) for a much larger sample of more than 1000 Galactic RRL stars in the case of the mid-infrared band (their Figure 3). We note here that the spread of the residuals of the PLZ relations is relatively low compared to, e.g., the relations presented by Neeley et al (2019; rms of around 0.18 mag).…”