Asymmetrical appearance of dark-cored filaments in sunspot penumbrae

¹ Sterrekundig Instituut Utrecht, Postbus 80 000, 3508 TA Utrecht, The Netherlands e-mail: P.Suetterlin@astro.uu.nl
² Kiepenheuer Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany

Received: 1 June 2004
Accepted: 2 June 2004

Abstract

Recent sunspot observations at unprecedented resolution have led to the discovery of dark cores in the bright filaments that form the penumbra ([CITE]). The discovery paper considered spots at disk center only, so the properties of the dark-cored filaments remain largely unknown. Here we analyze a speckle-reconstructed time series of G-band and blue continuum images of a sunspot acquired with the Dutch Open Telescope. The target was located at an heliocentric angle of 27 deg. We confirm the existence of dark-cored penumbral filaments also in spots outside the disk center, and report on distinct differences between the center and limb-side penumbra. In the inner center-side penumbra, filaments are detected as two narrow bright streaks separated by a central obscuration. These structures move together as a single entity. On the limb side, dark cores are hardly seen. The time series is used to determine the sizes (~200-250 km), proper motions (~280 m s^-1), and lifetimes (45 min) of typical dark-cored filaments.