AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 93. Quiet Photosphere, Chromosphere and Transition Region
Display, Thursday, June 3, 1999, 9:20am-4:00pm, Southeast Exhibit Hall

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[93.04] Comparisons of Sunspot Contrasts and Deficits on SOHO and San Fernando Observatory Continuum Images

S.R. Walton, D.G. Preminger, M. Mohageg (San Fernando Observatory, Cal State Northridge)

The San Fernando Observatory (SFO) Cartesian Full Disk Telescope (CFDT) instruments have produced a continuous series of thousands of daily full disk photometric solar images extending (in the case of CFDT1) to 1986. We have begun a project to compare sunspot properties measured on CFDT images to those measured by the continuum images produced by the Michaelson Doppler Interferometer (MDI) instrument on the SOHO spacecraft. Such a comparison requires an extended time period during which both CFDT and MDI took good data and during which there was extensive activity. We have chosen September 1997 as the first period for this comparison.

The SFO CFDT images were processed and restored according to the procedures described in Walton et al. (1996, Solar Phys. 179, 31) and Walton and Preminger (1999, Ap.J. 514, in press). As of this writing, preliminary comparisons have been made between SFO CFDT1 images (512 square, 5 arc second pixels) and MDI full disk continuum images (1024 square, 2.4 arc second pixels). Maximum (single pixel) and integrated sunspot contrast were compared for the largest sunspot in both images. In all cases, restoration of the CFDT images brings the two data sets into closer agreement, though differences remain.

We also compared the total photometric sunspot deficit integrated over all sunspot pixels. The agreement between the restored images and the SOI images is excellent. Further comparisons are required, but we tentatively conclude that restored SFO CFDT images can be reliably used to measure the total photometric sunspot deficit. This research was partially supported by NASA grants NAGW-3017 and NAGS-4973, and NSF grant ATM-9504374.

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