Doppler-shift oscillations in solar spicules

Georgian National Astrophysical Observatory (Abastumani Astrophysical Observatory), Kazbegi Ave. 2a, Tbilisi 0160, Georgia e-mail: temury@genao.org

Received: 18 April 2007
Accepted: 11 August 2007

Abstract

Aims.We analysed the consecutive height series of Hα spectra in solar limb spicules taken on the 53 cm coronagraph of Abastumani Astrophysical Observatory at the heights of 3800-8700 km above the photosphere. Our aim is to observe oscillatory phenomena in spicules and consequently to trace wave propagations through the chromosphere.

Methods.We use the Discrete Fourier Transform analysis of Hα Doppler shift time series constructed from the observed spectra at each height.

Results.Doppler velocities of solar limb spicules show oscillations with periods of 20-55 and 75-110 s. There is also clear evidence of 3-min oscillations at the observed heights.

Conclusions.The oscillations can be caused by wave propagations in thin magnetic flux tubes anchored in the photosphere. We suggest the granulation as a possible source of the wave excitation. Observed waves can be used as a tool for spicule seismology, and the magnetic field strength in spicules at the height of ~6000 km above the photosphere is estimated as  G.