Work

Theoretical RR Lyrae instability strip from MESA-RSP pulsation models and updated BaSTI evolutionary tracks

Year: 2026

Type: article

Abstract: Context. RR Lyraes (RRLs) are important tracers of old stellar populations and crucial distance indicators. To complement large variability surveys such as Gaia and Rubin-LSST, the topology of the RRL instability strip (IS) and their period-luminosity-metallicity (PLZ) and period-Wesenheit-metallicity (PWZ) relations must be updated using state-of-the-art stellar evolution and pulsation models. Aims. We employed the updated set of BaSTI horizontal branch (HB) evolutionary models, with finer sampling in effective temperature and metallicity, and computed the corresponding pulsation models using the MESA - RSP module. We aimed to quantify how the predicted IS boundaries and PLZ and PWZ relations depend on the adopted convection prescription and mixing-length parameter. Methods. We computed a grid of linear nonadiabatic radial pulsation models with MESA - RSP , covering −2.2 ≤ [Fe/H] ≤ + 0.06 dex. Seven convection configurations were explored including a recently empirically calibrated prescription for RRLs. Analytical IS boundaries were derived for RRab and RRc pulsators and transformed into several photometric systems (Gaia, OGLE, 2MASS, and LSST) and the Kiel diagram. Results. The updated evolutionary models do not substantially change the pulsation predictions: RRab IS edges agree well with previous results, while the RRc red edge is slightly redder. The width of the IS decreases systematically with increasing α MLT , and RRc is relatively more sensitive to the convection prescription than RRab. Testing both linear and quadratic edge fits, RRc IS favors a quadratic luminosity term in most cases, indicating intrinsic curvature of the first-overtone IS. The observed sample lies well within our predicted IS edges when compared in the ( J − K s) 0 versus M K s color–magnitude diagram. The PLZ and PWZ relations are also in good agreement with previous empirical and theoretical calibrations across the near-infrared bands; however, the convection prescription giving the closest match is wavelength-dependent. The theoretical Gaia PWZ relation shows a modest offset from the empirical Milky Way field relation, which diminishes significantly when compared at matching cluster metallicities. Conclusions. The predicted IS boundaries, PLZ and PWZ relations exhibit a coupled dependence on pulsation mode, metallicity, and convective treatment, with no single prescription performing uniformly best across all observational planes. The theoretical relations presented here are directly applicable to large RRL datasets from ongoing and forthcoming surveys, including Gaia and Rubin-LSST.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202662656