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Session 2 - Everything Else.
Display session, Friday, June 27
Ballroom C, Chair: Richard Canfield
Trying to determine solar vector magnetic fields from Zeeman-effect observations is a process made difficult by the realities of observational science at every step. The source of the largest errors in ground-based imaging spectropolarimetry is that the measurements span four dimensions, only two of which can be observed simultaneously. In the Imaging Vector Magnetograph at Haleakala, Hawaii, the polarization and spectral dimensions are obtained from a temporal sequence of images. Frame-to-frame distortion by atmospheric seeing causes spurious polarization and spectral signatures. We describe here a method of compensating, frame by frame, for not only rigid image translation but also differential image motion and blur in small areas of the image. The method relies on a second camera which records a broad-band image simultaneously with the main camera. The auxiliary "geometry" image is used to obtain a parametric model of the instantaneous seeing, which can then be used to correct the main image. The technique results in a factor of at least ten reduction in spurious polarization signal at spot boundaries, as well as an overall improvement in image fidelity.
Program listing for Friday