On the Relation between Umbral Dots, Dark‐cored Filaments, and Light Bridges

Abstract

We present high-resolution observations of the complex active region AR 0484 observed close to disk center with the Dunn Solar Telescope. The field of view (FOV) contains several interesting features, including a number of umbral fragments, light bridges of varying width, umbral dots, and dark-cored penumbral filaments. A time sequence of reconstructed G-band images and adaptive optics-corrected UBF filtergrams was analyzed with the goal of comparing observations with recent simulations and models of sunspot fine structure. In an umbral fragment in which the field strength is relatively weak, we find a large number of umbral dots. We were able to resolve dark substructure within bright umbral dots that in some cases resembles the dark lanes recently predicted by magnetohydrodynamic (MHD) simulations. Umbral dot substructure is also clearly revealed in images of spectral line parameters. We compare line parameters for dark-cored penumbral filaments, dark lanes observed in light bridges, and the dark umbral dot substructure. We find evidence that all of these structures are elevated above the formation height of the continuum. We observe dynamic proper motion of umbral dots, including motion along a narrow lane that occurs within an umbral fragment and shows similarity to the proper motion observed in narrow light bridges. Furthermore, we study the temporal variation of spectral line parameters such as the integrated line absorption of the temperature-sensitive Fe I λ5434 line. The computed power maps show features closely related to sunspot fine structure.