ar X iv : a st ro - p h / 97 10 03 4 v 1 2 O ct 1 99 7 The Evolution of Procyon A

A grid of stellar evolution models for Procyon A has been calculated. These models include the best physics available to us (including the latest opacities and equation of state) and are based on the revised astrometric mass of Girard et al. (1996). The long standing discrepancy between the evolutionary mass and the astrometric mass is now resolved, a result of the newly determined astrometric mass. Models were calculated with helium diffusion and with the combined effects of helium and heavy element diffusion. Oscillation frequencies for l = 0, 1, 2 and 3 p-modes (and g-modes) were calculated for these models. The predicted p-mode frequencies are relatively unaffected by heavy element diffusion and convective core overshoot. The inclusion of a modest stellar wind which effectively suppresses the helium diffusion in the surface layers has a modest effect on the p-mode frequencies. The evolutionary state (main sequence or shell hydrogen burning) of Procyon A has the largest effect on the predicted p-mode frequencies. The g-modes show a greater sensitivity to the various model parameters. The Procyon binary system consists of an F5 IV-V primary and a whitedwarf secondary in an 40.8 year orbit. The F5 primary (Procyon A) is a bright, nearby star with a well determined parallax and astrometric mass. As such, it presents a unique target for the study of non-radial stellar oscillations. Previous theoretical studies have pointed out that the astrometric mass was incompatible with the mass derived from stellar evolution calculations (Guenther & Demarque 1993). Procyon A was the target of a multi-site observing campaign (10 – 31 Jan/97) by the SONG project, whose goal was the detection of stellar oscillations. Motivated by these observations, as well as an improved mass determination for this star, we have re-examined the evolution and pulsation properties of Procyon A. The fundamental properties of Procyon A are: