A Brief Description of IUESIPS

The purpose of the IUESIPS system was to provide standard processed data and output products for IUE Guest Observers and archival users. The standardized extraction techniques generally worked best on well-exposed, point-source, continuum spectra (similar to the calibration stars). For many types of spectra, such as extended sources and weak spectra, customized extraction techniques may provide better quality data. To assist IUE data users in this, the archived IUE data files include all the major steps in the processing. Users may therefore employ customized techniques or algorithms at any point in the processing.

Because the IUESIPS system was in use for over 18 years, it went through a number of changes. However the basic processing steps and output files remained essentially the same.

• Raw image. The raw image data were retained intact and archived. The format is an image of 768 by 768 pixels in byte format (Data Numbers from 0 to 255).

• Photometrically corrected image. Each pixel was corrected to a linear scale of Flux Numbers (FNs) and an overall flat-field correction is applied.

• Geometrically corrected image. The image was corrected for camera-induced distortions. This file was explicitly produced only in IUESIPS Versions 1.0 and 1.1; the correction was implicitly handled in Version 2.0 (see the Summary of IUESIPS Changes and the IUESIPS Manual).

• Line-by-line file. This pseudo-image file was produced only for low-dispersion images, using the photometrically and geometrically corrected data. It consists of a swath around the spectrum or spectra which has been resampled so that the "lines" are aligned along the dispersion direction. The number of lines (perpendicular to the dispersion) and samples (along dispersion) changed twice in the software.

• Extracted file. The fully calibrated and extracted data were stored in this file. For low-dispersion data, arrays of the background, gross, and net flux (in FNs), the absoluted calibrated flux, wavelength, and epsilons (quality flags) are given. For high-dispersion data, the arrays are background, gross, net, and ripple-corrected fluxes (FNs), wavelength, and epsilons are given for each order. The absolutely calibrated flux arrays were added to the processing in 1990.

During the observations, an image header was generated documenting the details of the acquisition and the status of the instrument. Added to this header was a record of the image processing steps applied. The image header was appended to the output data files.

The output data files are stored in IUEGO format, an IUE-specific format that predates the common usage of FITS.

A complete description of the IUESIPS processing system is given in the IUESIPS Image Processing Information Manual. In addition, several published papers and IUE Newsletter articles describe various aspects of the processing and calibrations.

A list of the major changes in the processing system, as well as the complete IUESIPS Software Chronology, are also available.