Penumbral structure at 01 resolution

I. General appearance and power spectra

The Institute for Solar Physics of the Royal Swedish Academy of Sciences, AlbaNova University Center, 106 91 Stockholm, Sweden e-mail: rouppe,mats,dan,scharmer@astro.su.se

Corresponding author: L. H. M. Rouppe van der Voort, rouppe@astro.uio.no

Received: 16 April 2003
Accepted: 13 October 2003

Abstract

We analyse sunspot filtergrams of unprecedented quality obtained by [CITE] with the Swedish 1-m Solar Telescope on La Palma. The observations comprise images in three different wavelength bands: 488, 436, and 430 nm (G-band). We find that there are still unresolved penumbral filaments which must have widths smaller than 80 km. The fine structuring along the filaments is limited. Penumbral grains have internal structure and look like they are split or crossed by narrow dark structures. We calculate intensity power spectra of the penumbra from images that are corrected for seeing using the Phase Diversity technique. The effects of high order aberrations that are not corrected for are estimated to be too low to be consistent with a flat power spectrum. The penumbral power spectra do not show any signs of bumps or peaks that could correspond to a preferred scale at 035 for the width of penumbral filaments. We argue that the power spectrum is not a very reliable source of information concerning preferred scales.