Amplitudes of solar-like oscillations in red giants: Departures from the quasi-adiabatic approximation
1 LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
2 Institut d'Astrophysique et de Géophysique de l'Université de Liège, Allée du 6 Août, 17, 4000 Liège, Belgium
3 Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Knigstuhl 12, 69117 Heidelberg, Germany
4 Institut d'Astrophysique Spatiale, CNRS, Université Paris XI, 91405 Orsay Cedex, France
5 GEPI, CNRS, Observatoire de Paris, Université Denis Diderot, Place Jules Janssen, 92195 Meudon Cedex, France
a e-mail: firstname.lastname@example.org
CoRoT and Kepler measurements reveal us that the amplitudes of solar-like oscillations detected in red giant stars scale from stars to stars in a characteristic way. This observed scaling relation is not yet fully understood but constitutes potentially a powerful diagnostic about mode physics. Quasi-adiabatic theoretical scaling relations in terms of mode amplitudes result in systematic and large differences with the measurements performed for red giant stars. The use of a non-adiabatic intensity-velocity relation derived from a non-adiabatic pulsation code significantly reduces the discrepancy with the CoRoT measurements. The origin of the remaining difference is still unknown. Departure from adiabatic eigenfunction is a very likely explanation that is investigated in the present work using a 3D hydrodynamical model of the surface layers of a representative red giant star.
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