Astron. Astrophys. 360, 335-344 (2000)

The Sun's acoustic asphericity and magnetic fields in the solar convection zone

H.M. Antia ¹, S.M. Chitre ¹ and M.J. Thompson <sup>2

1</sup> Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
² Queen Mary and Westfield College, Astronomy Unit, Mile End Road, London E1 4NS, U.K.

Received 1 March 2000 / Accepted 19 May 2000

Abstract

The observed splittings of solar oscillation frequencies can be employed to separate the effects of internal solar rotation and to estimate the contribution from a large-scale magnetic field or any latitude-dependent thermal perturbation inside the Sun. The surface distortion estimated from the rotation rate in the solar interior is found to be in good agreement with the observed oblateness at solar surface. After subtracting out the estimated contribution from rotation, there is some residual signal in the even splitting coefficients, which may be explained by a magnetic field of approximately 20 kG strength located at a depth of 30000 km below the surface or an equivalent aspherical thermal perturbation. An upper limit of 300 kG is derived for a toroidal field near the base of the convection zone.

Key words: Sun: activity Sun: interior Sun: magnetic fields Sun: oscillations

Send offprint requests to: H.M. Antia

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. The technique
• 3. Results
  • 3.1. Shift in the mean frequency
  • 3.2. Oblateness due to rotation
  • 3.3. Second order splitting due to rotation
  • 3.4. Splitting due to magnetic field near the base of the convection zone
  • 3.5. Field in the upper convection zone
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: July 27, 2000
helpdesk.link@springer.de