A Recalibration of IUE NEWSIPS Low‐Dispersion Data

While the low dispersion IUE NEWSIPS data products represent a significantimprovement over original IUE SIPS data, they still contain serious systematiceffects which compromise their utility for certain applications. We show thatNEWSIPS low resolution data are internally consistent to only 10-15% at best,with the majority of the problem due to time dependent systematic effects. Inaddition, the NEWSIPS flux calibration is shown to be inconsistent by nearly10%. We examine the origin of these problems and proceed to formulate and applyalgorithms to correct them to ~ 3% level -- a factor of 5 improvement inaccuracy. Because of the temporal systematics, transforming the corrected datato the IUE flux calibration becomes ambiguous. Therefore, we elect to transformthe corrected data onto the HST FOS system. This system is far moreself-consistent, and transforming the IUE data to it places data from bothtelescopes on a single system. Finally, we argue that much of the remaining 3% systematic effects in thecorrected data is traceable to problems with the NEWSIPS intensitytransformation function (ITF). The accuracy could probably be doubled byrederiving the ITF.Comment: Submitted to ApJ Supplement, 35 pages, 13 figures, LaTeX - AASTEX aas2pp4.st