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Reading/Writing IUE FITS Data in IRAF/STSDAS
The original IUESIPS-generated data were archived in the Guest Observer ("GO") format, based on an obsolete version of the VICAR format. This format is not compatible with file readers supported by IRAF and STSDAS, which means that IUE data generated by IUESIPS cannot be read by them unless they are first rewritten to FITS (or ASCII) by an external package. NEWSIPS-generated files were stored as FITS binary files and can be accessed by a variety of FITS readers. However, NEWSIPS-generated files were stored in two different FITS structures, summarized as follows:
II. Additional Documentation
The reader may wish to consult documentation contained in the following sources:
III. The iuetools Package
In order to read MXLO/MXHI files, the user must have iuetools installed on his/her computer. This first requires IRAF version 2.11, STSDAS (version 2.0), and STSDAS/TABLES.
The iuetools package contains two tasks:
mxexpand: computes wavelength array from FITS header keywords and writes output file in form suitable for STSDAS and TABLES tasks.
mxtomultispec: extracts spectra in FITS binary tables created by mxexpand and outputs file in "multispec" (two-dimensional) format. This file can then be used in the onedspec package of IRAF/NOAO, such as splot.
1. Wavelength arrays: wavelengths in the MXLO (MXHI) order(s) are contained implicitly as header keywords, and can be expanded (calculated) into arrays via a linear dispersion relation. This calculation is the primary function of "mxexpand" task. Note that all wavelengths in NEWSIPS- generated data are monotonic as they refer to vacuum wavelengths.
2. Concatenating spectral orders: IRAF/STSDAS does not support scripts to splice MXHI orders. (To do this requires wavelength arrays and a designation of splice points. There are, however, IUEDAC routines which perform this function.) We recommend caution in writing software to merge spectral orders with a constant wavelength spacing since this requires a resampling of fluxes to a new wavelength grid.
3. Alternative to iuetools: If the user does not have iuetools installed, it is possible to read NEWSIPS MXLO files in IRAF. In that case one would have to first run another program to convert the MXLO table array to a primary array. For example, if IDL is available, one may use the IUEDAC task mxcon for this FITS-to-FITS file conversion (see http://archive.stsci.edu/iue/iuedacfits.html).
IV. Examples of Use of iuetools Package for MXHI Files
1. Reconnoitering your MXHI file, e.g. swp56875.mxhi:
Evaluate the structure of the MXHI/MXLO file (after loading STSDAS & TABLES):
ta> catfits swp58675.mxhi
EXT# FITSNAME FILENAME EXTVE DIMEN BITPI OBJECT 0 swp56875.mxhi 8 1 BINTABLE MEHI 17Fx60R
Note that swp56875.mxhi is a 3-dimensional binary table with 60 rows and 17 fields. Each of these fields may be a scalar or a vector of a fixed length (from IUE image to image) and is described in the NEWSIPS NEWSIPS Image Processing Manual, Chapter 12.9 (or Chapter12.8 for the 9 fields of MXLO files). The length of the wavelength or (various) flux fields is 768. This can be verified by executing 'catfits' with the "long" keyword set to "yes" for the extension file:
ta> catfits swp58675.mxhi long=yes
An extensive dump of the fits header is printed out. Keywords of the form TFORMxx, where xx denotes the number for the wavelength or flux fields gives the dimensionality, 768.
2. Using mxexpand for later work with STSDAS tasks:
3. Use of the mxtomultispec task:
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