Analysis of MDI High-Degree Mode Frequencies and their Rotational Splittings - AstrophysicsReport as inadecuate

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Abstract: Here we present a detailed analysis of solar acoustic mode frequencies andtheir rotational splittings for modes with degree up to 900. They were obtainedby applying spherical harmonic decomposition to full-disk solar images observedby the Michelson Doppler Imager onboard the Solar and Heliospheric Observatoryspacecraft. Global helioseismology analysis of high-degree modes is complicatedby the fact that the individual modes cannot be isolated, which has limited sofar the use of high-degree data for structure inversion of the near-surfacelayers r > 0.97 R. In this work, we took great care to recover the actualmode characteristics using a physically motivated model which included acomplete leakage matrix. We included in our analysis the following instrumentalcharacteristics: the correct instantaneous image scale, the radial andnon-radial image distortions, the effective position angle of the solarrotation axis and a correction to the Carrington elements. We also presentvariations of the mode frequencies caused by the solar activity cycle. We haveanalyzed seven observational periods from 1999 to 2005 and correlated theirfrequency shift with four different solar indices. The frequency shift scaledby the relative mode inertia is a function of frequency alone and follows asimple power law, where the exponent obtained for the p modes is twice thevalue obtained for the f modes. The different solar indices present the sameresult.

Author: M.C. Rabello-Soares, S.G. Korzennik, J. Schou


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