New Theoretical Period–Luminosity–Metallicity Relations for RR Lyrae in the Rubin-LSST Filters

Abstract

The revolutionary power of future Rubin-LSST observations will allow us to significantly improve the physics of pulsating stars, including RR Lyrae. In this context, an updated theoretical scenario predicting all the relevant pulsation observables in the corresponding photometric filters is mandatory. The bolometric light curves are based on a recently computed extensive set of nonlinear convective pulsation models for RR Lyrae stars, covering a broad range of metal content, and have been transformed into the Vera C. Rubin Observatory Legacy Survey of Space and Time (Rubin-LSST) photometric system. Predicted Rubin-LSST mean magnitudes and pulsation amplitudes have been adopted to build the Bailey diagrams (luminosity amplitude versus period) and the color–color diagrams in these bands. The current findings indicate that the g LSST–r LSST and r LSST–i LSST colors obey to a well-defined linear relation with the metal content. Moreover, the period–luminosity relations display in the reddest filters (r LSST, i LSST, z LSST, y LSST) a significant dependence on the assumed metal abundance. In particular, more metal-rich RR Lyrae are predicted to be fainter at a fixed period. Metal-dependent period–Wesenheit relations for different combinations of optical and near-infrared filters are also provided. These represent powerful tools to infer individual distances independently of reddening uncertainties, once the metal abundance is known and no relevant deviations from the adopted extinction law occur. Finally, we also derived new linear and quadratic absolute magnitude metallicity relations (g LSST versus [Fe/H]) and the metallicity coefficient is consistent with previous findings concerning the B and the V band.

Theoretical Stellar Pulsation Physics

“…the cases of Sculptor and Eridanus by Martínez-Vázquez et al 2016. Metal-dependent PW relations have also been derived for RR Lyrae, with the minimum metallicity effect corresponding to some combination of optical filters, such as B,V , that is predicted to be metal-insensitive, or g,r (see Marconi et al 2015Marconi et al , 2022. Moreover, the predicted metallicity dependence of RR Lyrae NIR PL and PW relations is in agreement with observations in Galactic globular clusters (see Bhardwaj et al 2023).…”

Photometric Metallicity and Distance for the Two RR Lyrae in Segue II and Ursa Major II Dwarf Galaxies Based on Multiband Light Curves

“…Similarly, we obtained 〈μ〉 = 17.58 ± 0.15 mag for UMaII-V1, and it is in good agreement with the estimated value given by Zucker et al (2006;∼17.5 ± 0.3 mag), based on the isochrone fitting, and is almost the same as the one determined in Vivas et al (2020;17.60 ± 0.20 mag) when including additional RR Lyrae for UMaII. We also found statistically consistent distance measurements to these two dwarf galaxies if independent theoretical PWZ relations from Marconi et al (2015Marconi et al ( , 2022 were adopted instead of the empirical relations.…”

Light-curve Recovery with the Vera Rubin Observatory’s LSST. I. Pulsating Stars in Local Group Dwarf Galaxies

“…Since the light curves become more and more scattered as the distance increases, mainly in the u, z, and y bands, we showed that a good recovery (at least for optical bands) is possible for the RR Lyrae and the short-period Cepheids up to Leo I at 0.26 Mpc, as demonstrated by fitting parameters reported in Table 3. In particular, we derived an accurate mean magnitude with a precision two orders of magnitude lower than the rms of the theoretical PL and PW relations derived by Marconi et al (2022). We point out that, when propagating the uncertainties on the PL/PW relations to derive distances, usually the propagation on the uncertainties of the coefficients is vanishing, while the error on the mean magnitudes and extinction dominate, being at least an order of magnitude larger.…”

“…To prove our new metric potential, we first studied the recovery of pulsating variable stars' light curves in a selected sample of LG galaxies. In recent work (Marconi et al 2022), we have shown that the application of the period-luminosity-metallicity (PLZ) and period-Wesenheit-metallicity (PWZ) relations to future Rubin LSST observations of RR Lyrae in a massive stellar system will represent a powerful tool to derive mean and individual distances. To make these relations useful, the mean magnitudes that we include must be recovered with an accuracy comparable to or better than the rms of the relations (around 0.1; see column 5 of their Table 5).…”

“…On the other hand, these relations can be used to derive the metallicity distribution of the investigated sample of pulsating stars, which is crucial to derive the chemical enrichment of the parent galaxy. Marconi et al (2022) have also shown the value of exploring the color-color diagram constructed from the intensityweighted mean magnitudes as a diagnostic tool to constrain the metallicity. The highest sensitivity to metallicity is revealed in the g-r versus u-g plane, while the r-i versus g-r diagram shows the best-defined relations.…”