Improved continuum definition in high-background IUE images

摘要

A technique is described for automatically filtering low-dispersion IUE images of untrailed point sources during extraction from the guest observer tape, for the purpose of reducing the effects of radiation events and bright pixels and obtaining improved definition of the continuum in long duration or high-background exposures. The method is based upon fitting a gaussian point-spread-function (PSF) to crosscuts of the sample orders in ESSR or LBLS files, which can be processed on a relatively small computer. Several adjacent crosscuts are binned during the fit to permit discriminating against errant samples lying directly along the dispersion line (and narrow spectral lines). The procedure results in a significant reduction of discrepancies in the fitted power-law indices for repeated exposures of faint BL Lac objects, compared with the results of previously attempted automatic filtering techniques.