Improved Cosmic Ray Rejection for Slitless Spectroscopic Data
Data from space based instruments such as the Advanced Camera for Survey (ACS) and the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) suffer from a high rate of cosmic ray hits, and elaborate techniques have been developed to identify these in the data reduction. In WFC3 IR data, cosmic ray hits are detected and rejected during the "up-the-ramp" fitting of the individual detector reads. For direct imaging, the MultiDrizzle software can detect deviant pixel values such as from cosmics when combining dithered data. We have implemented a similar technique in the aXe software package to be able to detect and flag deviant pixels in slitless spectroscopy data. In this contribution we introduce the method and demonstrate its application to WFC3/IR and ACS/WFC slitless data. We provide details on the number of previously unnoticed cosmics and give examples of improved extracted spectra. The limitations of the new method are also discussed.
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