Comparing convection in the Sun with Procyon A

Abstract

Abstract. As well as reproducing observable features like solar granulation, 3D simulations can provide useful information for local or non-local stellar modeling. Examples include testing out the mixing length theory in the surface layers, providing the turbulent correction for stellar models of p-mode frequencies, testing eddy viscocity prescriptions used in tidal dissipation models and comparing different closures of higher order moments. Having validated the 3D code with the sun we applied it to other stars. For Procyon A the turbulence is about twice as strong as it is in the Sun (estimated by the peak root mean square vertical velocity which is about 6.5 km/s) and the granules are nearly an order of magnitude larger, with plumes regularly extending down 2-3 pressure scale heights below the surface of Procyon A. An interesting feature of the Procyon simulation is that the horizontal layers in the vicinity of the granules appear to radially pulsate in a quasi-periodic manner. This makes the superadiabatic layer move in and out over a distance of about half a pressure scale height in a time of about 20-30 minutes. This motion appears to be tied to the granulation but there may be other phenomena involved such as some kind of local kappa-mechanism confined to the granulation surface layers. We find similar behaviour in a simulation of an 11 Gyr subgiant sun. As the velocities are more like the sun (about 3km/s), the time period of the pulsation in the subgiant is 2-3 times longer than in Procyon A.

The Nature ofp‐Modes and Granulation in Procyon: NewMOSTPhotometry and New Yale Convection Models

“…The convection modeling is described in Robinson et al (2005) and Robinson & Demarque (2007); modeling results for the Sun are described in Robinson et al (2003); comparisons of the convection modeling results for the Sun to other solar simulations is summarized in two reviews by Kupka (2005Kupka ( , 2008, in which he compares the Robinson et al (2003) to the work of Stein & Nordlund (1998) Although only a small piece of Procyon's convection zone is modeled (the largest box is 29 Mm ; 29 Mm ; 16:3 Mm), the simulation is physically realistic. A current equation of state (OPAL EOS2005; Rogers et al 1996) and opacities (OPAL2005 for high temperatures; Ferguson et al [2005] for low temperatures) are used.…”