Removal of Cosmic-Ray Events in Spectroscopic CCD Data

Current methods of treating cosmic ray events in CCD data images often fail for a variety of reasons. Cleaning of cosmic ray events from multifibre spectroscpic data is particularly difficult due to the variation in fibre response between exposures. With the development of large fibre systems (such as the 2 degree field (2dF) project on the Anglo-Australian Telescope (Taylor and Gray 1990), interactive cleaning of data frames is becoming the most time consuming task in reducing data. The advantages and disadvantages of some of the current non-interactive techniques are discussed, with particular emphasis toward cleaning multifibre data. In order to improve the detection and removal of cosmic ray events, a scaling technique that provides a better match between repeated frames has been developed. This technique has been used to create a new cleaning program that has a number of improvements over currently available programs.