A&A 489, 291-299 (2008)
Modeling the excitation of acoustic modes in Centauri AR. Samadi1, K. Belkacem1, M. J. Goupil1, M.-A. Dupret1, and F. Kupka2
1 Observatoire de Paris, LESIA, CNRS UMR 8109, 92195 Meudon, France
2 Max-Planck-Institute for Astrophysics, Karl-Schwarzschild Str. 1, 85748 Garching, Germany
Received 26 September 2007 / Accepted 30 May 2008
From different seismic observations we infer the energy supplied per unit of time by turbulent convection to the acoustic modes of Centauri A (HD 128620), a star that is similar but not identical to the Sun. The inferred rates of energy supplied to the modes (i.e. mode excitation rates) are found to be significantly higher than in the Sun. They are compared with those computed with an excitation model that includes two sources of driving, the Reynolds stress contribution and the advection of entropy fluctuations. The model also uses a closure model, the Closure Model with Plumes (CMP hereafter), that takes the asymmetry between the up- and down-flows (i.e. the granules and plumes, respectively) into account. Different prescriptions for the eddy-time correlation function are also compared to observational data. Calculations based on a Gaussian eddy-time correlation underestimate excitation rates compared with the values derived from observations for Centauri A. On the other hand, calculations based on a Lorentzian eddy-time correlation lie within the observational error bars. This confirms results in the solar case. Compared to the helioseismic data, those obtained for Centauri A constitute an additional support for our model of excitation. We show that mode masses must be computed taking turbulent pressure into account. Finally, we emphasize the need for more accurate seismic measurements in order to distinguish between the CMP closure model and the quasi-normal approximation in the case of Centauri A, as well as to confirm or not the need to include the excitation by the entropy fluctuations.
Key words: convection -- turbulence -- stars: oscillations -- stars: atmospheres
© ESO 2008