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Astron. Astrophys. 351, 689-700 (1999)


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Convective contributions to the frequencies of solar oscillations

C.S. Rosenthal 1, J. Christensen-Dalsgaard 1,2, Å. Nordlund 3,4, R.F. Stein 5 and R. Trampedach 1,2

1 Teoretisk Astrofysik Center, Danmarks Grundforskningsfond, Aarhus Universitet, 8000 Aarhus C, Denmark
2 Institut for Fysik og Astronomi, Aarhus Universitet, 8000 Aarhus C, Denmark
3 Niels Bohr Institutet for Astronomi, Fysik og Geofysik, Astronomisk Observatorium, Kobenhavns Universitet, Denmark
4 Teoretisk Astrofysik Center, Danmarks Grundforskningsfond, Juliane Maries Vej 30, 2100 Kobenhavn O, Denmark
5 Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA

Received 20 March 1998 / Accepted 21 May 1999

Abstract

Differences between observed and theoretical eigenfrequencies of the Sun have characteristics which identify them as arising predominantly from properties of the oscillations in the vicinity of the solar surface: in the super-adiabatic, convective boundary layer and above. These frequency differences may therefore provide useful information about the structure of these regions, precisely where the theory of solar structure is most uncertain.

In the present work we use numerical simulations of the outer part of the Sun to quantify the influence of turbulent convection on solar oscillation frequencies. Separating the influence into effects on the mean model and effects on the physics of the modes, we find that the main model effects are due to the turbulent pressure that provides additional support against gravity, and thermal differences between average 3-D models and 1-D models. Surfaces of constant pressure in the visible photosphere are elevated by about 150 km, relative to a standard envelope model.

As a result, the turning points of high-frequency modes are raised, while those of the low-frequency modes remain essentially unaffected. The corresponding gradual lowering of the mode frequencies accounts for most of the frequency difference between observations and standard solar models. Additional effects are expected to come primarily from changes in the physics of the modes, in particular from the modulation of the turbulent pressure by the oscillations.

Key words: Sun: interior – Sun: oscillations

Present address: Institute of Theoretical Astrophysics, P.O. Box 1029, Blindern, Oslo, Norway (colinr@astro.uio.no)

Send offprint requests to: C.S. Rosenthal

© European Southern Observatory (ESO) 1999

Online publication: November 3, 1999

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