Diffraction Pattern Analysis of Bright TRACE Flares

A study of the diffraction patterns seen in TRACE images of bright flare kernels was undertaken to better understand the properties of the telescope. The diffraction pattern caused by light from a bright flare kernel passing through the mesh supporting the filters at the front of the TRACE telescope has been examined, and a method has been developed to use this pattern to determine the zeroth order intensity of flares that cannot be measured directly due to saturation of the Analog to Digital Converter (ADC) in the CCD detection package. The validity of this method is confirmed by testing it on a flare that does not saturate the ADC. The diffraction pattern allows us to measure intensities far brighter than the detection package allows; the range has been effectively increased by at least 41 times. The light scattered from any point was observed to be ≈20%, a significant amount which may be affecting the image quality of the telescope. An accurate determination of the ratio of the square slit size to slit spacing of the wire mesh was obtained. 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. This effect is caused by two principal wavelengths, Fe ix at 171.073 Å and Fe x at 174.507 Å in the TRACE 171 Å passband. This study is a part of the TRACE Team educational outreach program.