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Issue A&A Volume 412, Number 1, December II 2003 Page(s) 249 - 255 Section Diffuse matter in space DOI 10.1051/0004-6361:20031305

A&A 412, 249-255 (2003)
DOI: 10.1051/0004-6361:20031305

Dynamics of the solar active region finestructure

B. Bovelet and E. Wiehr

Universitäts-Sternwarte, Geismarlandstraße 11, 37083 Göttingen, Germany
(Received 22 May 2003 / Accepted 11 August 2003)

Abstract
We investigate the dynamical behavior of the finestructure in a sunspot's surroundings and its penumbra from a speckle-reconstructed 60 min time series taken at the 45 cm Dutch Open Telescope (DOT) on La Palma. In the 1 nm spectral window containing the G-band, we determine the area of each feature and its time evolution by means of pattern recognition, particularly adapted to separate bright granular edges from inter-granular G-band bright points (BP). The evolution of each individual BP shows a stronger variation of the area than of the intensity. We analyze the horizontal motions of BP as a function of their distance from the sunspot center. Within a 6 Mm ring around the outer sunspot border, most BP (4/5) move radially outwards; they are faster than the minority (1/5) of inward moving BP. The difference of both velocities indicates a radial outward drift which decreases from about 0.3 km s ^-1 at the outer penumbral border to zero at about 20 Mm distance (28´´) from the sunspot center; a spatial range that we interpret as the extension of the sunpot "moat". This finding supports the idea of giant rolls in deep layers measured by helio-seismic tomography and predicted by theory. Inside the penumbra, we find a 4/5 majority of penumbral bright structures (PBS) to move inwards with a mean velocity of 0.8 km s ^-1. The 1/5 minority of outward moving PBS is almost entirely located in the outer penumbra; their mean velocity of 0.8 km s ^-1 is equally found for penumbral dark structures (PDS) in the outer penumbra, in agreement with penumbral MHD models.

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

Offprint request: E. Wiehr, ewiehr@uni-sw.gwdg.de

© ESO 2003

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