The flow field in the sunspot canopy

Rezaei, R.; Schlichenmaier, R.; Beck, C.; Bellot Rubio, L. R.
Bibliographical reference

Astronomy and Astrophysics, Volume 454, Issue 3, August II 2006, pp.975-982

Advertised on:
8
2006
Number of authors
4
IAC number of authors
0
Citations
36
Refereed citations
30
Description
Aims.We investigate the flow field in the sunspot canopy using simultaneous Stokes vector spectropolarimetry of three sunspots (θ=27°, 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 O_2-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.