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Spherical and Aspherical Structure of the Sun: First Year of Soho/Mdi Observations

Published online by Cambridge University Press:  08 February 2017

A.G. Kosovichev ,
R. Nigam ,
P.H. Scherrer ,
J. Schou ,
J. Christensen-Dalsgaard ,
W.A. Dziembowski ,
P.H. Goode ,
D.O. Gough ,
J. Reiter  and
E.J. Rhodes Jr.
A.G. Kosovichev
Affiliation:
W. W. Hansen Experimental Physics Lab., Stanford University, U.S.A.
R. Nigam
Affiliation:
W. W. Hansen Experimental Physics Lab., Stanford University, U.S.A.
P.H. Scherrer
Affiliation:
W. W. Hansen Experimental Physics Lab., Stanford University, U.S.A.
J. Schou
Affiliation:
W. W. Hansen Experimental Physics Lab., Stanford University, U.S.A.
J. Christensen-Dalsgaard
Affiliation:
Teoretisk Astrofysik Center, Danmarks Grundforskningsfond Institut for Fysik og Astronomi, Aarhus Universitet, Denmark
W.A. Dziembowski
Affiliation:
Copernicus Astronomical Center, Poland
P.H. Goode
Affiliation:
Big Bear Solar Observatory, New Jersey Institute of Technology, U.S.A
D.O. Gough
Affiliation:
Institute of Astronomy and Department of Applied Mathematics and Theoretical Physics, University of Cambridge, U.K.
J. Reiter
Affiliation:
Technische Universität München, Germany
E.J. Rhodes Jr.
Affiliation:
University of Southern California, U.S.A.

Abstract

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We report the initial results of one year of continuous observations of the Sun‘s internal structure from the Michelson Doppler Imager (MDI) on board SOHO. The results have been obtained by inverting frequencies of p and f modes determined with two different methods of averaging over split multiplets. Small systematic differences between the two frequency sets depend primarily on mode frequencies, and, thus, did not significantly affect the inversions. A preliminary study of the systematic effects resulting from asymmetry of oscillation power peaks has also shown no significant influence on the inversion results. The inferred sound-speed profile is in general agreement with the previous data from MDI and ground-based networks. In the energy-generating core, the resolution is substantially improved, and the inversion results indicate a sharp negative perturbation of the sound speed in the core, tending to a positive value near the center. High-precision measurements of the f-mode frequencies have been used to determine the seismic radius of the Sun. The global asphericity estimated from frequency variation across the split mode multiplets has been found to be small, and is consistent with the asphericity during the previous activity minimum. Variations of the solar frequencies during the first year of MDI observations have also been detected.

Type
III. Large-Scale Structure of the Sun
Information
Symposium - International Astronomical Union , Volume 185: New Eyes to See Inside the Sun and Stars , 1998 , pp. 157 - 164
Copyright
Copyright © Kluwer 1998 

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