EDP Sciences
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Volume 403, Number 1, May III 2003
Page(s) 303 - 312
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20030356

A&A 403, 303-312 (2003)
DOI: 10.1051/0004-6361:20030356

Numerical constraints on the model of stochastic excitation of solar-type oscillations

R. Samadi1, 2, Å. Nordlund3, R. F. Stein4, M. J. Goupil2 and I. Roxburgh1, 2

1  Astronomy Unit, Queen Mary, University of London, London E14NS, UK
2  Observatoire de Paris, LESIA, CNRS UMR 8109, 92195 Meudon, France
3  Niels Bohr Institute for Astronomy Physics and Geophysics, Copenhagen, Denmark
4  Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan, USA

(Received 7 November 2002 / Accepted 7 March 2003)

Analyses of a 3D simulation of the upper layers of a solar convective envelope provide constraints on the physical quantities which enter the theoretical formulation of a stochastic excitation model of solar p modes, for instance the convective velocities and the turbulent kinetic energy spectrum. These constraints are then used to compute the acoustic excitation rate for solar p modes, P. The resulting values are found ~ 5 times larger than the values resulting from a computation in which convective velocities and entropy fluctuations are obtained with a 1D solar envelope model built with the time-dependent, nonlocal Gough (1977) extension of the mixing length formulation for convection (GMLT). This difference is mainly due to the assumed mean anisotropy properties of the velocity field in the excitation region. The 3D simulation suggests much larger horizontal velocities compared to vertical ones than in the 1D GMLT solar model. The values of P obtained with the 3D simulation constraints however are still too small compared with the values inferred from solar observations. Improvements in the description of the turbulent kinetic energy spectrum and its depth dependence yield further increased theoretical values of P which bring them closer to the observations. It is also found that the source of excitation arising from the advection of the turbulent fluctuations of entropy by the turbulent movements contributes ~ $65{-}75 \%$ to the excitation and therefore remains dominant over the Reynolds stress contribution. The derived theoretical values of P obtained with the 3D simulation constraints remain smaller by a factor ~ 3 compared with the solar observations. This shows that the stochastic excitation model still needs to be improved.

Key words: convection -- turbulence -- stars: oscillations -- Sun: oscillations

Offprint request: R. Samadi, Reza.Samadi@obspm.fr

© ESO 2003

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