Solar 5-min Oscillation Amplitude Anisotropy and Doppler Velocity Systematics
Several measurements of 5-min velocity amplitudes have yielded confusing and conflicting information on the l and m dependence of the modal excitation (Kuhn and O’hanlon, 1983 - henceforth KO; Deubner, 1985; and Hill et al. 1985). We have obtained considerably more data than was described in KO using similar observing techniques. Additional analysis has illuminated a systematic effect related to the finite spatial resolution, and line asymmetry of the data that can lead to errors in inferred velocity amplitudes. Even though Doppler shifts are calculated from the Fraunhofer line center positions the effect can lead to 5-min oscillation amplitude errors at the 10 percent or greater level. Line wing observations should be more susceptible, and comparable resolution 2-dimensional data may be less sensitive to this systematic.
KeywordsPoint Spread Function Line Profile Doppler Velocity Velocity Amplitude Line Wing
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