Asteroseismology of double-mode radial Scuti stars: AE Ursae Majoris and RV Arietis

We construct complex seismic models of two high-amplitude delta Sct stars, AE UMa and RV Ari, each pulsating in two radial modes: fundamental and first overtone. Besides the frequencies of two radial modes, the models also reproduce the amplitude of bolometric flux variations (the non-adiabatic parameter f) for the dominant mode. Applying the Monte-Carlo-based Bayesian analysis, we derive strong constraints on the parameters of the model, as well as on the free parameters of the theory. A vast majority of seismic models of the two stars are just at the beginning of hydrogen-shell burning and a small fraction are at the very end of an overall contraction. The stars have a similar age of about 1.6Gyr for the hydrogen-shell burning phase. Both stars have unusual low overshooting from the convective core, about 0.02 and 0.004 of the pressure scaleheight for AE UMa and RV Ari, respectively. This result presumably indicates that overshooting should vary with time and scale with a decreasing convective core. The efficiency of convection in the envelope of both stars is low and is described by the mixing length parameter alpha(MLT) of about 0.3-0.6. The third frequency of RV Ari, confirmed by us in the Transiting Exoplanet Survey Satellite (TESS) photometry, can only be associated with mixed non-radial modes l = 1, g(4)-g(8) or l = 2, g(10)-g(12). We include the dipole mode into our Bayesian modelling and demonstrate its huge asteroseismic potential.