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Z. A. Frank (LMSAL), A. C. Lin (Palo Alto High School), R. W. Nightingale, T. D. Tarbell (LMSAL)
A study of the diffraction patterns seen in TRACE images of bright flares was undertaken to better understand the properties of the telescope. The pattern caused by light from a bright solar flare passing through the wire mesh in front of the telescope has been examined, and a method has been developed to use this pattern to determine the zeroth order intensity of bright flares. This intensity cannot usually be measured directly due to saturation of the Analog to Digital Converter (ADC) electronics in the CCD camera package. The validity of this method has been tested on dimmer flares, whose intensity do not saturate the ADC. The diffraction pattern allows us to measure intensities far brighter than the camera package permits. For the bright flare on May 16, 1999 at 13:49:21 UT the range has been effectively increased by at least 41 times. The light defracted away from any point was observed to be 18%, a significant amount which affects the contrast of TRACE images. An accurate determination of the ratio of the square slit size to slit spacing of the wire mesh has been obtained. This is an important parameter for a deconvolution routine that can remove the diffraction patterns from the image (see adjacent SPD poster paper by Tarbell et al.). Wavelength dispersion, the phenomenon that as the higher order diffracted peaks lie further from the center they spread out until double peaks are observed, has also been examined as part of this study. This effect is observable because there are two principal wavelengths, Fe IX at 171.06 Å and Fe X at 174.52 Å in the TRACE 171 Å passband used in present analysis. This study is a part of the TRACE Team educational outreach program and is supported by contract NAS5-38099 at LMSAL.