Problems in measuring prominence oscillations

Abstract

Time variations of Doppler shifts of the Ca+ 8542 Å emission in quiescent solar prominences have been measured. A new type of ’limb guider’ assures a highly constant distance of the spectrograph slit from the solar limb and furthermore removes low frequency image motion in the direction perpendicular to the slit. Abstract. Remaining image motion along the slit is usually removed by a correlation of subsequent spectra. This procedure, however, cannot be applied globally to the whole spatial height in the spectra if individual structures exhibit lateral motions along the slit or even decay or arise during the observation.We therefore correlate defined individual emission maxima from successive spectra. The finally obtained power spectra show oscillations with a variety of periods at restricted locations. The data favour theknown general presence of periods near 20 and 60 min, howeverthey give only slight indication for ‘typical’ periods near 3 and 5 min.