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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
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.