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P. Demarque, F.J. Robinson (Yale U.), D.B. Guenther (Saint Mary's U., Canada), Y.-C. Kim (Yonsei U., Korea), K.L. Chan (Hong Kong U. Sci. and Tech., China)
We present a 3D radiative-hydrodynamical simulation of the surface layers of Procyon A, and compare it to a similar simulation for the Sun. Procyon has a thin outer convection zone, and its atmosphere, like the solar atmosphere, is characterized by granulation. Procyon granules are much larger than in the Sun, with a mean diameter near 10,000 km, in comparison with 1,200 km for a solar granule. The dynamics of the Procyon atmosphere differ from the solar atmosphere dynamics in fundamental ways: (1) the ratio of turbulent to gas pressure is larger in the Procyon atmosphere (2) the highly superadiabatic transition layer (SAL) is located at much shallower optical depth (3) the location of the SAL maximum moves back and forth in the atmosphere, from an optically thin to optically thick region in a quasi-periodic manner. This motion is driven by the penetration of granules into the outermost atmospheric layers while they overturn. The timescale of this phenomenon is roughly half the full granule lifetime (which is typically in the range of 40 to 60 minutes); (3) the maximum temperature contrast at a given optical depth varies rapidly on a short timescale resulting in locally large radiative losses and strong intensity contrasts (hot spots). The simulation also shows that the autocorrelation timescale in Procyon's atmosphere is favorable to the stochastic excitation of p-modes by turbulence. However highly efficient radiative damping in Procyon's atmosphere is likely to result in much shorter p-mode coherence lifetimes than in the Sun.
This research was supported in part by NASA grant NAG5-13299 (PD), the NASA EOS/IDS Program (FJR), NSERC of Canada (DBG) and the Korea Research Foundation grant KRF-2003-015-C00249 (YCK).
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.