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Astron. Astrophys. 348, L37-L40 (1999)

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Letter to the Editor

Infrared lines as probes of solar magnetic features

XV. Evershed flow in cool, weak penumbral fields

I. Rüedi 1, S.K. Solanki 1 and C.U. Keller 2

1 ETH-Zentrum, Institute of Astronomy, CH-8092 Zürich, Switzerland
2 National Solar Observatory, NOAO *, P.O. Box 26732, Tucson, AZ 85726, USA

Received 2 July 1999 / Accepted 14 July 1999


Observations of Ti [FORMULA] lines at 2.2 µm show that the Evershed flow takes place in cool, almost horizontal channels with a low magnetic field strength ([FORMULA] G) that does not appear to change significantly across the penumbra. This property might allow an outward directed siphon flow to exist along such cool flux tubes.

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

* Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.

Send offprint requests to: I. Rüedi

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999