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Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
R. Albrecht, R. N. Hook and H. A. Bushouse, e
Ö Copyright 1998 Astronomical Society of the Pacific. All rights reserved.
ds.
An IRAF Port of the New IUE Calibration Pipeline
Richard A. Shaw and Howard A. Bushouse
Space Telescope Science Institute, Baltimore, MD 21218, Email:
shaw@stsci.edu
Abstract. The calibration pipeline that was used for the IUE fi­
nal archive, NEWSIPS, is being ported to IRAF. This port will enable
archival researchers to optimize the spectral processing for their scientific
needs.
1. Introduction
A new spectral image processing system (NEWSIPS) was constructed for a final,
archival reprocessing of the IUE data archive. NEWSIPS incorporates many im­
proved processing algorithms and calibrations which greatly enhance the quality,
and hence the scientific utility, of IUE data for archival research. However, the
perceived need to produce a homogeneous archive precluded custom processing
options and special calibrations that are essential for many science programs. In
addition, limited resources prevented the completion of certain useful calibra­
tions, and limited the scope of e#orts to characterize the complex echelle back­
ground and ripple correction. Unfortunately, it is not practical for researchers
to make use of the production NEWSIPS system, mostly because it depends on
vendor­specific software and hardware, and it would have been impossible for
users to maintain or enhance the pipeline over the long term.
We are porting the NEWSIPS software to the IRAF environment. The
ported pipeline will enable recalibration from the raw data or from certain in­
termediate stages, will allow for di#erent choices of reference files, and will ac­
commodate the use of more appropriate processing techniques at intermediate
stages. We are removing the dependencies of NEWSIPS on licensed vendor soft­
ware, and replacing them where necessary with existing or new IRAF libraries.
Our goal is to retain a high degree of compatibility with the archival NEWSIPS
pipeline, given the same input parameters. Placing the NEWSIPS software in
the public domain will allow IUE archival researchers much greater flexibility
for meeting their particular scientific needs, while also promoting greater under­
standing of the NEWSIPS system by current and future users of IUE data. The
IRAF system is a good choice for ensuring the longevity, portability, and wide
accessibility to the user community of the software, while also providing a very
rich environment for analysis of IUE data by future archival researchers.
103

104 Shaw and Bushouse
2. Why Recalibrate?
There are many reasons for re­running all or part of the NEWSIPS calibration
pipeline, even after all the improvements that have been realized by the original
NEWSIPS processing. For example, the spectral extraction processing for low
dispersion uses an ``optimal'' or signal­weighted extraction technique (SWET) to
optimize the S/N ratio and exclude outliers. However, this technique is inappro­
priate if the ionization structure is spatially resolved---e.g., for many planetary
nebulae or H ii regions. Figure 1 shows how outlier rejection in SWET can cause
unexpected results; the solution is to re­extract using a di#erent method.
Figure 1. Low dispersion spectrum from LWP 17531 of # Her show­
ing the SWET extraction (upper ), which excludes a spatially resolved
emission feature that can be recovered with a boxcar extraction (lower ).
The high­dispersion extraction uses a simple boxcar weighting, and as such
does not exclude outliers. Figure 2 illustrates the e#ect of a prominent, grazing
cosmic ray that a#ected several adjacent orders in the SWP high­dispersion
spectrum of BD+75 # 325. Cosmic rays like this could easily be excluded using
either a more sophisticated extraction or, when two or more images are available
in the archive, by rejecting cosmic rays from the LI image during calibration.
For images obtained in high­dispersion, an imperfect model of the back­
ground determination can under some circumstances result in an under­ or
over­correction. These problems are illustrated in Figure 3, where the SWP
spectrum of HD 149438 shows what should be a saturated absorption feature at
Ly #. An under­correction of the inter­order background causes this absorption
feature not to fall to zero flux in the line core. The opposite problem occurs for
HD 163181, where an over­correction for the inter­order background shortward
of 1250 š A results in negative fluxes. Improvements in the background estimation
will require either a more sophisticated model or a semi­empirical approach.
More ambitious users may need to improve upon the calibration reference
files to extract the best science from their data. For example, the most appro­
priate flat­field data for late­epoch SWP images may be that obtained during
the 1992 ITF campaign. But a lack of resources precluded the construction,

An IRAF Port of the New IUE Calibration Pipeline 105
testing, and implementation for final archive processing. For cases like this, the
only option is for users to reprocess their images with improved calibrations.
3. Software Details
The NEWSIPS pipeline, various ancillary utilities, and the calibration reference
files will be distributed as an IRAF layered package called iue. The complete
calibration pipeline, caliue, will be a high­level script that executes several tasks
that comprise major modules of the pipeline. These tasks, listed in Table 1,
can also be run independently. The choice of what calibration steps will be
performed, and of which calibration reference files will be used, will be managed
through a set of keywords stored in the image header, or alternatively through
parameters of the constituent tasks. A feature of this approach is that the ported
pipeline will be re­entrant---i.e., it will be possible to use di#erent (perhaps user­
written) software to perform one or more of the calibration steps, then run the
remainder of the standard pipeline tasks.
Table 1. Major Tasks in the newsips Pipeline.
Task Description
ns init Populates the raw image header with control keywords
rawscreen Flags missing data and cosmic rays
ttdc Computes time­ and temperature­dependent dispersion corrections
xcorr Registers the science image with the ITF
photom Applies the photometric correction
iuegeom Rectifies the 2­D spectra and linearizes the dispersion
nsextract Extracts the 1­D spectrum from the image
One of the goals of this project is to reorganize and better document the
calibration reference files used in NEWSIPS, and to provide them to the com­
munity in FITS format. The iue package will also include tools for constructing
the calibration reference files, which will enable archival users to improve upon
or extend the calibrations derived for the final archive. The ported pipeline
will support FITS format for all input and output files natively, eliminating
the dependency on MIDAS­format files. Other enhancements include improved
memory management by a factor of #10 3 or more, which will enable reprocessing
multiple images at once for large archival projects. Finally, an essential element
in this port is to eliminate the dependency of NEWSIPS on vendor­proprietary
software so that it may be distributed freely to the community.
4. Availability
The first release of the iue layered package is planned for early 1998. This re­
lease will contain the low­dispersion portion of NEWSIPS pipeline, including
some custom processing options. It will also include utilities for creating vari­
ous calibration reference files. Subsequent releases during 1998 will include the

106 Shaw and Bushouse
high­dispersion portion of the processing pipeline, additional custom processing
options, and new utilities. The iue package, including the software, documen­
tation, calibration reference files, and all updates, will be available from the
NEWSIPS home page 1 . Note that the iue package will require that IRAF V2.11
and TABLES V2.0 (or later) be installed. The IUE archive is being re­hosted
to the Space Telescope Science Institute, where support for IUE archival data
and this NEWSIPS port will continue for the foreseeable future.
Acknowledgments. This software project is funded by the NASA Astro­
physics Data Program through grant NAS5--32697 to ST ScI.
1 http://ra.stsci.edu/newsips/

An IRAF Port of the New IUE Calibration Pipeline 107
Figure 2. Several adjacent spectral orders are a#ected by a grazing
cosmic ray hit (marked with arrows) on the high dispersion image SWP
35674 of BD+75 # 325.
Figure 3. High dispersion SWP spectra of two stars, illustrating the
consequences of an imperfect background model in NEWSIPS.