The size of penumbral fine structure

Abstract

I present power spectra of penumbral and granular intensity variations from a speckle-restored G-band image sequence of sunspot NOAA 9407 taken on April 1, 2001 with the Dutch Open Telescope on La Palma. I compare spatial power spectra of the sunspot penumbra with spatial power spectra from granulation with and without filigree. Relative to the granular power distribution, the penumbral power spectrum is enhanced over a wide range in spatial frequency peaking at 0."35. For smaller scales, the penumbral power distribution closely resembles that of the granular intensity variations. In contrast, the power spectrum of granulation with filigree exhibits increased power down to the resolution limit of 0."22, indicating the presence of unresolved magnetic elements.