Astronomy & Astrophysics

A&A 454, 975-982 (2006)
DOI: 10.1051/0004-6361:20065180

The flow field in the sunspot canopy

R. Rezaei¹, R. Schlichenmaier¹, C. Beck¹ and L. R. Bellot Rubio^{1, 2}

¹ Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany
e-mail: rrezaei@kis.uni-freiburg.de
² Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, 18080 Granada, Spain

(Received 10 March 2006 / Accepted 28 March 2006)

Abstract
Aims.We investigate the flow field in the sunspot canopy using simultaneous Stokes vector spectropolarimetry of three sunspots ( $\theta=27\degr$ , 50°, 75°) and their surroundings in visible (630.15 and 630.25 nm) and near infrared (1564.8 and 1565.2 nm) neutral iron lines.
Methods.To calibrate the Doppler shifts, we compare an absolute velocity calibration using the telluric O₂-line at 630.20 nm and a relative velocity calibration using the Doppler shift of Stokes V profiles in the umbra under the assumption that the umbra is at rest. Both methods yield the same result within the calibration uncertainties (~150 m s^-1). We study the radial dependence of Stokes V profiles in the directions of disk center and limb side.
Results.Maps of Stokes V profile shifts, polarity, amplitude asymmetry, field strength and magnetic field azimuth provide strong evidence for the presence of a magnetic canopy and for the existence of a radial outflow in the canopy.
Conclusions.Our findings indicate that the Evershed flow does not cease abruptly at the white-light spot boundary, but that at least a part of the penumbral Evershed flow continues into the magnetic canopy.

Key words: Sun: photosphere -- Sun: sunspots -- Sun: magnetic fields

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