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Astron. Astrophys. 335, L97-L100 (1998)

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Letter to the Editor

Oscillations of sunspot magnetic fields

I. Rüedi 1, S.K. Solanki 1, J.O. Stenflo 1, T. Tarbell 2 and P.H. Scherrer 3

1 Institute of Astronomy, ETH-Zentrum, CH-8092 Zürich, Switzerland
2 Lockheed Martin Research Laboratory, Department H1-12, Bldg. 252, Palo Alto, CA 94304, USA
3 W.W. Hansen Experimental Physics Laboratory, Center for Space Science and Astrophysics, Stanford University, Stanford, CA 94305-4085, USA

Received 24 April 1998 / Accepted 27 May 1998

Abstract

We report on velocity and magnetic field oscillations observed in sunspots using the MDI instrument onboard SOHO. In addition to the well-known velocity oscillations, the data clearly show highly localised oscillations of the magnetogram signal in different parts of the sunspots. We show that only oscillations of the magnetic field vector can produce the observed magnetogram oscillations, and that the observed phase relations suggest an origin in terms of magnetoacoustic gravity waves.

Key words: Sun: activity – magnetic fields – oscillations – photosphere – sunspots

Send offprint requests to: I. Rüedi

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© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998
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