Spiral-shaped wavefronts in a sunspot umbra

Advertised on
C. Kuckein
I. Thaler

There are many oscillatory phenomena in the Sun which show up from the deepest interior layers to the outermost layers of its atmosphere. The study of these waves is a fundamental problem in solar physics, since they are one of the candidates proposed to explain the high temperatures measured in the chromosphere and the corona of the Sun, and they are used to characterize the structure of the Sun using seismological analyses. In this work we have studied wave propagation in sunspots. Sunspots are caused by strong concentrations of magnetic field, visible on the solar disc as dark regions. The study has identified the presence of oscillations in spiral form which start out from the darkest part of the sunspot, called the umbra, and spread into the outer regions, the penumbra. Using several instruments from the GREGOR telescope, at the Teide Observatory, we have been able to work out the geometry of the magnetic field of the sunspot, and relate its orientation to the apparent direction of propagation of the waves. These waves has been interpreted as evidence for magneto-acoustic waves which propagate from the interior of the Sun out to high layers of the atmosphere, along the direction of the magnetic field lines.