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As part of the effort to produce a uniformly processed and calibrated final archive of IUE data, all aspects of the photometric correction, image resampling, spectral extraction, wavelength calibration, and absolute flux calibration have been revised. These new derivations have significantly reduced the errors in absolutely calibrated spectral data compared to the originally processed data.
To ensure an accurate detector photometric correction for all images in the archive, full 2-D calibrations of the detectors were re-acquired in 1992 for both prime cameras. These new photometric calibrations combined with an improved raw image registration technique (which correlates the photometric calibration with the science image) represent a dramatic improvement over the previous calibrations.
Several new image resampling techniques have been created which also represent an improvement over the original processing. These include corrections for the spatial deviations (cross-dispersion ``wiggles''), and the change of scale needed to linearize the dispersion.
The absolute flux scale for Final Archive data is set from previous UV experiment data of standard stars in the 2100--2300\AA\ region. However, a notable departure from the previous flux calibration of IUE data is the use of models of white dwarf atmospheres to determine the relative flux scale for the entire IUE spectral region. In addition, flux corrections which compensate for both time and temperature dependent sensitivity degradations of the IUE detectors (a step not employed in the original processing) are included in the final calibration.
This work has been supported under NASA contract NAS5-31230 to Computer Sciences Corporation.
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