Hiroko Watanabe — Page 2

arXiv2007

Umbral Fine Structures in Sunspots Observed with Hinode Solar Optical Telescope

High resolution imaging observation of a sunspot umbra was done with Hinode Solar Optical Telescope (SOT). Filtergrams in wavelengths of blue and green continuum were taken during three consecutive days. The umbra consisted of a dark core region, several diffuse components and numerous umbral dots. We derived basic properties of umbral dots (UDs), especially their temperatures, lifetimes, proper motions, spatial distribution and morphological evolution. Brightness of UDs is confirmed to depend on the brightness of their surrounding background. Several UDs show fission and fusion. Thanks to the stable condition of space observation, we could first follow the temporal behavior of these events. The derived properties of internal structure of the umbra are discussed in viewpoint of magnetoconvection in a strong magnetic field.

astro-ph↗

arXiv2007

Small Scale Magnetic Flux Emergence Observed with Hinode/Solar Optical Telescope

We observed small scale magnetic flux emergence in a sunspot moat region by the Solar Optical Telescope (SOT) aboard the Hinode satellite. We analyzed filtergram images observed in the wavelengths of Fe 6302 angstrom, G-band and Ca II H. In Stokes I images of Fe 6302 angstrom, emerging magnetic flux were recognized as dark lanes. In G-band, they showed their shapes almost the same as in Stokes I images. These magnetic flux appeared as dark filaments in Ca II H images. Stokes V images of Fe 6302 angstrom showed pairs of opposite polarities at footpoints of each filament. These magnetic concentrations are identified to correspond to bright points in G-band/Ca II H images. From the analysis of time-sliced diagrams, we derived following properties of emerging flux, which are consistent with the previous works. (1) Two footpoints separate each other at a speed of 4.2 km/s during the initial phase of evolution and decreases to about 1 km/s in 10 minutes later. (2) Ca II H filaments appear almost simultaneously with the formation of dark lanes in Stokes I in the observational cadence of 2 minutes. (3) The lifetime of the dark lanes in Stokes I and G-band is 8 minutes, while that of Ca filament is 12 minutes. An interesting phenomena was observed that an emerging flux tube expands laterally in the photosphere with a speed of 3.8 km/s. Discussion on the horizontal expansion of flux tube will be given with refernce to previous simulation studies.

astro-ph↗