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Astron. Astrophys. 324, 298-310 (1997)


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Solar internal rotation from LOWL data

A 2D regularized least-squares inversion using B-splines

T. Corbard 1, G. Berthomieu 1, P. Morel 1, J. Provost 1, J. Schou 2 and S. Tomczyk 3

1 Laboratoire G.-D. Cassini, CNRS URA 1362, Observatoire de la Côte d'Azur, BP 229, F-06304 Nice Cedex 4, France
2 Hansen Experimental Physics Laboratory, Annex A201, Stanford University, Stanford, CA 94305-4085, USA
3 High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307, USA

Received 9 December 1996 / Accepted 21 January 1997

Abstract

Observations of surface oscillations of the Sun can be analyzed to probe the solar interior. We use data obtained by the LOWL instrument (LOWL is an abbreviation for low degree with degree denoted by L) installed on Mauna Loa, Hawaii, since 1994 to investigate solar internal rotation. A 2 Dimensional Regularized Least-Squares (2D RLS) inverse method based on an expansion of the solution on B-splines of arbitrary order is presented and applied to a 2 year dataset. This method insures the regularity of the solution in the center and introduces surface constraints. The choice of trade-off parameters in the regularization term is discussed using an L-curves analysis and we discuss the influence of the choice of the order of derivatives in the regularization terms for the description of the deep interior. We study the latitudinal resolution of the inversion of a-coefficients compared to that of the inversion of individual splittings built from these coefficients.

Compared to the previous inversion of the first three months of LOWL data made by Tomczyk et al. (1995b), our solution is extended up to the surface by adding high degree modes and constraining the rotation to fit the spectrographic observations (Snodgrass 1984). In the radiative zone we obtain more rigid rotation and our solution is compatible with a rotation of the solar core of the order or smaller than the surface rotation at mid latitude.

Key words: Sun: interior – Sun: oscillations – Sun: rotation – methods: numerical

Send offprint requests to: T. Corbard

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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