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

Abstract

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. The models reproduce, besides the frequencies of two radial modes, also the amplitude of bolometric flux variations (the 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 is at the very end of an overall contraction. The stars have a similar age of about 1.6 Gyr 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 scale height 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 rather low and described by the mixing length parameter alphaMLT of about 0.3-0.6. The third frequency of RV Ari, confirmed by us in the TESS photometry, can only be associated with mixed nonradial modes l=1, g4-g8 or l=2, g10-g12. We include the dipole mode into our Bayesian modelling and demonstrate its huge asteroseismic potential.