Recent High Resolution Observations and Interpretations of Sunspot Fine Structure

摘要

We review analyses made of highly resolved filtergrams, magnetograms and Dopplergrams of sunspots, recorded with the Swedish 1-meter Solar Telescope (SST) on La Palma. Dark cores in penumbral filaments are shown to be directly linked to peripheral umbral dots and to dark lanes in light bridges, suggesting similar or related underlying physics. The visibility of dark cores is found to depend strongly on the azimuth angle already for spots located at small heliocentric distances. It is shown that dark cores are clearly visible close to the center of the Ca II H line, formed approximately 150-200 km above the photosphere. We conclude that the T 1 layer of dark-cored filaments outlines a strongly warped surface, consistent with the finding that the magnetic field strength is strongly reduced in dark cores. We show that several properties of dark-cored filaments derived from SST data are consistent with results of inversions of low-resolution Stokes spectra, but also find important discrepancies with the interpretation that penumbral filaments can be identified with flux tubes. Our data are consistent with the model proposed by Spruit Scharmer (2006), explaining dark cores as signatures of field-free convection occurring just below the visible surface of the penumbra. We discuss recent simulations of light bridges and umbral dots, providing additional support to that model.