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Issue A&A Volume 378, Number 3, November II 2001 Page(s) 1078 - 1086 Section The Sun DOI 10.1051/0004-6361:20011156

A&A 378, 1078-1086 (2001)
DOI: 10.1051/0004-6361:20011156

2D-spectroscopy of the Evershed flow in sunspots

J. Hirzberger^{1, 2} and F. Kneer<sup>1

1</sup>  Universitäts-Sternwarte, Geismarlandstraße 11, 37083 Göttingen, Germany
²  Institut für Geophysik, Astrophysik und Meteorologie, Universitätsplatz 5, 8010 Graz, Austria

(Received 28 March 2001 / Accepted 16 August 2001)

Abstract
The radial variation of the Evershed flow in two small sunspots (NOAA 8737 and NOAA 9145) is studied by means of two-dimensional spectrograms of high spatial resolution. We find a systematic decrease of the flow velocity with photospheric height and a shift of the velocity maximum towards larger penumbral radii in higher layers but no clear correlation between flow velocity and continuum intensity. At the outer penumbral boundaries the Evershed flow ceases abruptly and even downward directed flow velocities in the deepest probed photospheric layers were found. Furthermore, granules adjacent to the penumbral boundary show a systematic redshift of their spot-side parts which is attributed to fast, eventually supersonic, downflows between them and the penumbral boundary.

Key words: Sun: photosphere -- sunspots -- Sun: granulation -- techniques: spectroscopic

Offprint request: J. Hirzberger, jhirzbe@uni-sw.gwdg.de

© ESO 2001

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