Umbral dots: clues to the internal structure of sunspots

Sunspots have been studied since the time of Galileo, but they still remain one of the most active research fields in solar physics. Especially, research on the fine structure of sunspots made great progress with the advent of the Hinode satellite and CRISP spectropolarimetry at the Swedish Solar Telescope on La Palma.

Umbral dots (UDs) are tiny bright points observed in the umbra of sunspots. They are scientifically interesting because they are manifestations of the interaction between strong magnetic field and convection (magnetoconvection). Using seeing-free images of a sunspot, we measured the size, lifetime, and proper motion of UDs, and their magnetic field. The results show that the lifetime of UDs is constant regardless of field strength, and that the motion speed of UDs increases as the field inclination at their emergence site gets larger. I will also present preliminary results of the flow field of umbral dots observed at very high spatial resolution.


21/10/2010 - 14:00
Hiroko Watanabe
University of Kyoto