HR: 0830h
AN: SP11B-08    [Abstracts]
TI: New Steps Towards the Unbiased Characterization of High-Degree Mode Frequencies
AU: * Rabello-Soares, M C
EM: csoares@quake.Stanford.EDU
AF: Stanford University, Hansen Experimental Physics Laboratory, Stanford, CA 94305 United States
AU: Korzennik, S G
EM: skorzennik@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 United States
AU: Schou, J
EM: schou@quake.Stanford.EDU
AF: Stanford University, Hansen Experimental Physics Laboratory, Stanford, CA 94305 United States
AB: Bias in the characterization of high-degree mode frequency results from the blending of individual modes into ridges as mode lifetimes get shorter and spatial leaks get closer in frequency at high degrees. To recover the actual underlying mode frequency from fitting the ridge, an accurate model of the amplitude of the peaks that contribute to the ridge power distribution is crucial. Such a model requires that the instrumental characteristics be very well understood and very precisely measured. We here present new results from our continuing effort to estimate unbiased high-degree mode frequencies using full-disk data from the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). The methodology is based on the extensive analysis presented in Korzennik et al (2004) - and will in turn be beneficial to MDI, GONG and eventually HMI. The key improvement on our previous work is the re-decomposition of the images onto spherical harmonic component. This new spatial decomposition incorporates specific MDI instrumental characteristics, like a more accurate plate scale, our best model of the image distortion, the image orientation, etc... These instrumental effects were introduced one at a time and their effect carefully compared to the predictions of our model. As expected, by including these corrections in the spatial decomposition, the residual corrections that must be applied to the ridge frequency are reduced, leading to a less biased frequency estimation.
DE: 7522 Helioseismology
SC: Solar Physics Division - AAS [SP]
MN: 2005 Joint Assembly