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

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 <sup>2

1</sup> 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

Abstract

Observations of Ti lines at 2.2 µm show that the Evershed flow takes place in cool, almost horizontal channels with a low magnetic field strength ( 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

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Observational results
  • 2.1. The observations
  • 2.2. Comparison with other observations
• 3. Standard siphon flow models
• 4. Evershed flow in interchange flux tubes
• 5. Discussion and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999
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