Theoretical Pulsation Properties of RR Lyrae and Type II Cepheids in the JWST and Roman photometric systems

Abstract

RR Lyrae (RRL) stars and Type II Cepheids (T2Cs) are key standard candles and tracers of old stellar populations. The deep, wide-field capabilities of facilities such as the James Webb Space Telescope (JWST) and the Nancy Grace Roman Space Telescope will significantly expand their utility as a Population II alternative to Classical Cepheids for distance scale calibrations. We present theoretical pulsation properties-including light-curve morphologies, amplitudes, and multi-filter relations for RRLs (Z = 0.0001 - 0.02, M = 0.51 - 0.80, Msun) and T2Cs (Z = 0.0001 - 0.01, M = 0.495 - 0.65, Msun) to enable detailed studies of Galactic and extragalactic populations. Using alreday available non-linear convective pulsation models, we converted their predicted bolometric light curves across various chemical compositions and evolutionary stages into the JWST and Roman photometric systems. From these, we derived multi-filter Period-Amplitude and Color-Color diagrams, alongside Period-Luminosity and Period-Wesenheit relations with explicit metallicity terms. RRL relations display a significantly stronger zero-point metallicity dependence than those of T2Cs, despite sharing similar slopes. Consequently, T2Cs offer a distance scale indicator that is remarkably robust against metallicity uncertainties. As a preliminary test, we applied our metal-dependent Period-Wesenheit relations to a subset of JWST-observed RRLs in the WLM galaxy, deriving a distance modulus of mu_0 = 24.85 +/- 0.03 mag (assuming the literature average metallicity). The derived distance to WLM is consistent with most literature values, though slightly shorter than determinations based on Classical Cepheids and the Tip of the Red Giant Branch. These theoretical relations pave the way for future high-precision distance determinations and asteroseismic diagnostics with JWST and Roman.