Proper motions in sunspots
After all the excitement of sunspot group 798/808 in September and the recent annular eclipse, the Sun has been pretty exciting in the last month or so. On astro-ph today there was an article, which will appear in a future issue of the Astrophysical Journal, describing high-resolution observations of sunspots. The researchers looked at the cooler penumbral regions with a resolution of about 0.1 arcseconds, watching the motions of the plasma above the surface. They all work for the Instituto de Astrofisica de Canarias, Spain, and on their website they have a collection of movies of these motions. They are all mpegs and are quite large (tens of megabytes), but they are worth the wait.
Solar astronomers already knew there were convective motions in the penumbral regions, but the measured velocities were not high enough to carry away as much heat as they should be doing. These guys used old data taken with a telescope less than one metre in diameter (don't look at the Sun!) equipped with adaptive optics which provided diffraction-limited images. What they found, by watching the movements of filaments within the penumbra, were vertical motions (similar to thse seen in convection cells elsewhere on the Sun's surface) with average velocities of 200 m/s. To carry away enough heat by convection, the velocities would have to be more like 1 km/s, but in the conclusions the researchers point out that the limited resolution of their data may lead to an underestimate of the motions. The mystery is not solved, but now there is more information for the theorists who build models of the Sun to try and work out exactly what is going on.