Abstract
Differences between the solar rotation axis and that of a spherical-harmonic decomposition of imaged helioseismic data cause power from each mode to be erroneously resolved into other nearby modes with the same spherical harmonic degree l, but somewhat different values of the azimuthal order m. In the long-term average, this leakage artificially broadens the line width of each mode, decreases the peak power, and produces an asymmetrical line profile that pulls the line centroid toward the m = 0 frequency. The magnitude of these effects depends on the values of l, m, and the error angle. Angular difference of a few tenths of a degree at intermediate ls (50–150) can produce line broadening of up to 20%, apparent peak-power reductions of up to 10%, and line centroid errors of up to a few nanoHertz.
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Kennedy, J.R. Effects of Polar-Angle Errors in Imaged Helioseismology. Solar Physics 175, 15–26 (1997). https://doi.org/10.1023/A:1004943609574
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DOI: https://doi.org/10.1023/A:1004943609574