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Paper: The IUE Final Archive -- Scientific Evaluation and Results with NEWSIPS Data
Volume: 61, Astronomical Data Analysis Software and Systems III
Page: 127
Authors: de La Pena, M. D.; Nichols-Bohlin, J.; Levay, K. L.; Michalitsianos, A.
Abstract: The culmination of the IUE Project will be the creation of a Final Archive which will contain all scientific and calibration data acquired during the mission, processed in a consistent and homogenous fashion, using an enhanced image processing system designed specifically for this purpose. Fundamental observational and image processing parameters will be incorporated into the headers of the image data files, and compiled into an IUE Project Database, further enhancing the utility of the archival information. Data processed for the Final Archive will begin to be available during 1993. The Final Archive data reduction system, NEW Spectral Image Processing System (NEWSIPS), utilizes innovative image processing techniques in order to achieve an improved signal-to-noise ratio (S/N) in the extracted spectrum. Specifically, NEWSIPS employs: an image registration algorithm and a ``raw space'' Intensity Transfer Function (ITF) which yield a more accurate photometric correction; a flux conserving resampling which maps the data to a geometric space where the echelle orders are parallel to an image axis and the wavelength dispersion is linear within each order; and a signal-weighted extraction method. NEWSIPS achieves a significant increase in the S/N in the two-dimensional images, and ultimately, in the extracted spectra. The increase in the S/N for low-dispersion data ranges from 10 -- 50 percent, with factors of 2 -- 4 improvement in some cases. The greatest improvements have been seen in under-exposed, high radiation, and high sky background images. The S/N for NEWSIPS data is often better than that of the IUESIPS data for a single spectrum, and multiple NEWSIPS images can be co-added to attain further increases in the S/N. Preliminary results from the high-dispersion system suggest a comparable improvement in S/N to that obtained for low-dispersion. Examples of the improvements in the data are presented. The Goddard IUE Project Database will contain the basic observational parameters for each exposure ( i.e., accurate coordinates and exposure times, homogeneous names for objects) and the image processing parameters of NEWSIPS. The observational parameters for every exposure have been verified in a consistent way to ensure the accuracy and clarity of the information; the image processing parameters are statistical indicators of image quality. These database parameters are potent tools that will allow the archival researcher to determine in an efficient way the best data available to achieve specific scientific goals.
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