Line-of-sight velocity measurements using a dissector-tube. II: Time variations of the tangential velocity component in the Evershed effect

• Published in: Astronomy and astrophysics (Berlin) 1993-09, Vol.277 (1), p.242-248
• Main Authors: DRUZHININ, S. A, PEVTSOV, A. A, LEVKOVSKY, V. L, NIKONOVA, M. V
• Format: Article
• Language: eng ; rus
• ISSN: 0004-6361; 1432-0746

We present the results of measurements of sunspot torsional oscillations. For six sunspots, a study was made of the spectral composition of Doppler velocity signals from two areas of penumbra, symmetric about the sunspot umbra located near the limb. The spectrograph slit was directed parallel to the nearest solar limb. The observations were made in the lines Fe I 543.45 nm and H-beta 486.13 nm using a dissector tube. Its electronic scanning was controlled in such a way that two channels measure spectral line shifts in two different parts of the photocathode. The results of the work indicate that the sunspot penumbra exhibits several kinds of oscillations: quasi-five-min vertical oscillations of small areas of penumbra (4 arcsec), vertical oscillations of large areas of penumbra (periods from 20 min to 1 h), and the sunspot torsional oscillations. Periodic variations in sunspot position are observed to have an amplitude of about 1 arcsec and periods close to those of the sunspot torsional oscillations.