NEW OBSERVATIONS OF 5 MINUTE OSCILLATIONS IN THE OPPOSITE FLANKS OF SOLAR FRAUNHOFER LINES .1. THE EFFECT OF VARYING THE SPECTRAL AND TEMPORAL RESOLUTION

Results of an investigation of the rms wavelength fluctuations in the 5-min range, at fixed intensity levels, in the opposite flanks of 15 Fe I and two Fe II lines, selected from the range 6200-6400 A are presented. Critical values for these quantities are evaluated. The number of used lines makes it possible to analyze the height dependence of the oscillations within the photosphere, and a clear correlation between the formation height of the emergent intensity and the ratio of the oscillation power in the two flanks of the lines is found. The existence of a unique relationship, independent of the characteristics of the single lines, confirms the diagnostic value of this ratio to investigate the variations of the wave properties throughout the solar atmosphere. The effect is argued to be due to radiative damping, which produces a height-dependent phase shift between velocity and thermodynamic perturbations within the line-forming region.