The Sun's Hydrostatic Structure from LOWL Data

Sarbani Basu, J. Christensen-Dalsgaard,
Teoretisk Astrofysik Center, Danmarks Grundforskningsfond,
Institut for Fysik og Astronomi, Aarhus Universitet,
DK-8000 Aarhus C, Denmark

J. Schou,
Center for Space Physics and Astrophysics, HEPL Annex 201,
Stanford University, CA 94305

M. J. Thompson,
Astronomy Unit, Queen Mary and Westfield College,
Mile End Road, London E1 4NS, UK

S. Tomczyk
High Altitude Observatory, NCAR,
P.O. Box 3000, Boulder, CO 80307

Abstract. Recent observations with the LOWL instrument have for the first time provided a uniform set of frequencies that allow detailed inversion for the structure of much of the Sun's deep interior. We present the results of inverting the LOWL data and compare them with the corresponding results obtained using inhomogeneous data sets from more than one instrument. Furthermore, improvements in the description of the required physics motivates the calculation of new solar models. Thus we present results of inversions of the LOWL data against several reference models using up-to-date physics. In models including the gravitational settling of helium, the sound speed and density agree with the Sun to within substantially better than 1%. We test various modifications to the physics of the models, to see if the remaining small (but significant) discrepancy between the Sun and the models can be removed. We find that none of the modifications tested can adequately account for the remaining discrepancy, though a small increase in helium diffusion in the core gives a modest improvement over the standard diffusion model. Finally, we find that the seismic data support theoretical calculations which indicate that settling of heavier elements has reduced the present surface value of Z by about 8% relative to its mean interior value.

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