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IUE Data Products

The MAST IUE archive contains files processed with two different image processing systems: NEWSIPS and IUESIPS. The official IUE final archive was created using NEWSIPS, and all NEWSIPS files are archived using FITS format. These are the recommended files for MAST users. The original IUE image processing system was known as IUESIPS. IUESIPS files are available in either the project-defined GO format, or the IUE Data Analysis Center derived RDAF format. (RDAF and GO format files can be easily converted to one another using available IUEDAC IDL routines.)

In order to reduce file transfer times, files requested via the web are downloaded using one of three compression options:

  • .tar - uncompressed files bundled in a tar file. (Note, prior to 10/21/99, the individual files were also gzipped by default.)
  • .tar.gz - files are bundled into a tar file which is then compressed using gzip.
  • .zip - files are bundled (and compressed) into a zip file,

File requested via FTP are downloaded as individual gzipped files. For more information on downloading and reading IUE files on different platforms see the data retrieval help page. More information on the individual IUESIPS and NEWSIPS files is given below. Clicking on the data type names listed below will display the detailed file descriptions as described in the IUE image processing information manuals.


  • MXLO, MXHI - The merged extracted spectral files contain the absolutely-calibrated fluxes, wavelengths, data quality flags, and sigmas (or noise estimate for MXHI files) in a FITS binary table extension. The high dispersion files are named MXHI and the low dispersion files are MXLO. Note that although low dispersion double aperture exposures are listed as two separate entries on the search results page, both spectra are contained in one MXLO file.
  • SILO SIHI - The resampled image files (SILO & SIHI) are the files from which the fluxes were extracted. The SI files contain the photometrically-corrected and rotated image as a primary array, wavelength information in a binary table extension, and an image extension containing an array of data qualiy flags. These files are useful for identifying camera artifacts such as cosmic ray hits, etc.
  • RILO,RIHI, LILO,LIHI - The RILO, RIHI raw image files (a 768x768 byte primary array image) and the LILO, LIHI linearized image files (a 768x768 integer primary array file with associated data quality flags as a 768x768 integer array image extension) are also available.

IUESIPS GO-Format Files

  • MELO,MEHI - The merged extracted spectral files containing scaled vectors of wavelengths, and gross, background, net and absolutely-calibrated net fluxes for each extracted spectral order.
  • ELBL - Available for low dispersion images only, these are the extended line-by-line (spatially-resolved) files from which the extracted fluxes are obtained. Useful for identifying reseaux and camera artifacts. Pixel values are stored in IUE FN units.
  • RI - The 768x768 raw image files containing a VICAR label (as do all IUESIPS files), and 768 records of 768 bytes each.