Comparison of High-degree Solar Acoustic Frequencies and Asymmetry between Velocity and Intensity Data

TL;DR

This study compares high-degree solar acoustic frequencies derived from velocity and intensity data, revealing differences in asymmetry and frequency that depend on the data type and observational parameters.

Contribution

It provides a detailed analysis of the asymmetry and frequency differences between velocity and intensity helioseismic data using asymmetric peak profile fitting.

Findings

Velocity asymmetry is negative across all frequencies.

Intensity asymmetry shows complex, frequency-dependent behavior.

Frequency differences are mainly due to fitting methods, not physical effects.

Abstract

Using the local helioseismic technique of ring diagram we analyze the frequencies of high--degree f- and p-modes derived from both velocity and continuum intensity data observed by MDI. Fitting the spectra with asymmetric peak profiles, we find that the asymmetry associated with velocity line profiles is negative for all frequency ranges agreeing with previous observations while the asymmetry of the intensity profiles shows a complex and frequency dependent behavior. We also observe systematic frequency differences between intensity and velocity spectra at the high end of the frequency range, mostly above 4 mHz. We infer that this difference arises from the fitting of the intensity rather than the velocity spectra. We also show that the frequency differences between intensity and velocity do not vary significantly from the disk center to the limb when the spectra are fitted with the asymmetric profile and conclude that only a part of the background is correlated with the intensity oscillations.