A closure model with plumes

II. Application to the stochastic excitation of solar p modes

¹ Observatoire de Paris, LESIA, CNRS UMR 8109, 92195 Meudon, France e-mail: Kevin.Belkacem@obspm.fr
² Max-Planck-Institute for Astrophysics, Karl-Schwarzschild Str. 1, 85741 Garching, Germany
³ Institut d'Astrophysique Spatiale, CNRS/Université Paris XI UMR 8617, 91405 Orsay Cedex, France

Received: 5 April 2006
Accepted: 22 June 2006

Abstract

Context. Amplitudes of stellar p modes result from a balance between excitation and damping processes taking place in the uppermost part of convective zones in solar-type stars and can therefore be used as a seismic diagnostic for the physical properties of these external layers.

Aims. Our goal is to improve the theoretical modelling of stochastic excitation of p modes by turbulent convection.

Methods. With the help of the closure model with plume (CMP) developed in a companion paper, we refine the theoretical description of the excitation by the turbulent Reynolds stress term. The CMP is generalized for two-point correlation products so as to apply it to the formalism developed by Samadi & Goupil (2001, A&A, 370, 136). The excitation source terms are then computed with this improvement, and a comparison with solar data from the GOLF instrument is performed.

Results.The present model provides a significant improvement when comparing absolute values of theoretical amplitudes with observational data. It gives rise to a frequency dependence of the power supplied to solar p modes, which agrees with GOLF observations. It is shown that the asymmetry of the turbulent convection zone (up and downflows) plays a major role in the excitation processes. Despite an increase in the Reynolds stress term contribution due to our improved description, an additional source of excitation, identified as the entropy source term, is still necessary for reproducing the observational data.

Conclusions.Theoretical excitation rates in the frequency range now are in agreement with the observational data from the GOLF instrument. However, at lower frequencies, it exhibits small discrepancies at the maximum level of a few per cent. Improvements are likely to come from a better physical description of the excitation by entropy fluctuations in the superadiabatic zone.