Foullon, C. (Claire) and Nakariakov, V. M. (Valery M.). (2010) Independent signals from the influence of internal magnetic layers on the frequencies of solar p-modes. The Astrophysical Journal. Letters, Vol.714 (No.1). L68-L72. ISSN 2041-8205

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Abstract

The discovery that p-mode frequencies of low degree do not follow changes of solar surface activity during the recent solar minimum offers the possibility of a new diagnostic signature of the responsible pressure perturbation in the wave guiding medium, potentially rich of information regarding the structure of the Sun and the cause of the unusually long solar minimum. Magnetic fields, as well as temperature changes, introduce equilibrium pressure deviations that modify the resonant frequencies of p-mode oscillations. Assuming the perturbation to be caused by a horizontal layer of magnetic field located in a plane-stratified model of the Sun, we compile analytical frequency shifts and process them to allow direct comparison with observations. The effect of magnetism itself on the central p-mode frequencies can be neglected in comparison with the thermal effect of a perturbative layer buried in the solar interior. A parametric study shows that a layer as thin as 2100 km at subsurface depths is able to reproduce reported mean anomalous frequency shifts (not correlated with the surface activity), while a layer of size around 4200 km increasing by a small amount at depths near 0.08 R-circle dot can explain individual low-degree shifts. It is also possible to obtain the mean shifts via the upward motion through depths near 0.03 R-circle dot of a rising perturbative layer of thickness around 7000 km. Hence, the anomalous frequency shifts are best explained by thermal effects in the upper regions of the convection zone. The effects of latitudinal distribution are not treated here.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Magnetic fields, Helioseismology, Sun -- Internal structure, Solar oscillations
Journal or Publication Title:	The Astrophysical Journal. Letters
Publisher:	Institute of Physics Publishing, Inc.
ISSN:	2041-8205
Date:	1 May 2010
Volume:	Vol.714
Number:	No.1
Number of Pages:	5
Page Range:	L68-L72
Identification Number:	10.1088/2041-8205/714/1/L68
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
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URI:	http://wrap.warwick.ac.uk/id/eprint/6051

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