Penumbral velocity oscillations

Doppler velocity variations of four sunspot penumbrae were observed in November 1988 at the Observatorio del Teide, Tenerife, using the spectral line Fe i 5576 Å. All of the penumbrae show local power maxima in the five-minute range, while no power is found around three minutes. This indicates that the five-minute oscillations are still present in the penumbrae, but the direction of the velocities might be tilted by the magnetic field. On the other hand, the maxima of the power and of the Evershed flow do not always occur at the same locations.The Gregory-Coudé telescope is operated by the Universitäts-Sternwarte Göttingen in cooperation with the Kiepenheuer-Institut für Sonnenphysik in Freiburg and the Institut für Astronomie und Astrophysik der Universität Würzburg.