Information on the IUE Gzipped ASCII files


The MXLO gzip file

The gzipped ASCII files of low dispersion spectra are available for downloading from the IUE preview page. If your browser automatically ungzips the file and displays it, you can still download the file by clicking on the "gzipped ASCII file" link using the right mouse button. The files consist of an abbreviated header followed by the original, unsmoothed spectral data. Note that although the long wavelength spectral plots were truncated at 3200 Å, the ASCII files contain data out to ~3350 Å.

The contents of the header include: 

 Index Content                         Example
 ^^^^^^^^^^^^^                         ^^^^^^^
   1   Disclaimer                      NOT ORIGINAL PROJECT DATA PRODUCT
   2   EID + dispersion + aperture     SWP1707LOWLARGE
   3   Object ID                       NGC 7009
   4   RA  (1950)                      21:01:30
   5   DEC (1950)                      -11:34:00
   6   IUE Object Class                70
   7   Trailed flag                    NO-TRAIL
   8   Segmented exposure flag         NO
   9   Exposure time (seconds)         119.473
  10   Observation date dd/mm/yy       03/06/78
  11   Observation time (UT)           17:47:00
  12   Observation day of year         154
  13   THDA at start of exposure       9.50
  14   Processing date dd/mm/yy        12/10/95
  15   Processing station              GSFC
  16   JD of observation               2443663.24097
  17   Estimated max continuum in DN   79
  18   Mean background in DN           23

Immediately following the header are 6 columns of numbers. There are 495 rows of data for the SWP files and 563 rows for the LWP/LWR files. The format of each row is f7.2, 2e10.2, 3i6, e.g., 

1150.58  4.75e-12  1.26e-12   272    85     0
1152.26  2.02e-12  1.09e-12   271    38     0
1153.93  2.57e-12  1.04e-12   270    51     0

These columns represent (in order): 

     Quantity                    Units
     ^^^^^^^^                    ^^^^^
     Wavelength                  Å
     Flux                        erg cm-2 sec-1 Å-1
     Standard deviation          erg cm-2 sec-1 Å-1
     Background level            IUE Flux Numbers (FN)
     Net spectrum                IUE Flux Numbers (FN)
     IUE data quality (nu) flag  numbered code


The MXHI gzip file

The files available for downloading from the browser page are gzipped ASCII files which consist of an abbreviated header, a combined order spectrum resampled onto a uniform grid with a spacing of either 0.05 or 0.10 Å (for short or long wavelength spectra), and its accompanying noise and background vectors (all in ergs/cm^2/s/Ang)). The flux and error vectors are the weighted mean of the original points which fell in the 0.05 (0.10) Å bin and the weighted error in the mean. An entry of -1 in the flux vector implies that all the nu flags for the data in that bin were < -512 (see above). The corresponding noise vector then has an entry of +1. Otherwise, the flags were ignored in the rebinning procedure.

The contents of the header are: 

 Index Content                         Example
 ^^^^^^^^^^^^^                         ^^^^^^^
   1   Disclaimer                      NOT ORIGINAL IUE PROJECT DATA PRODUCT
   2   EID + dispersion + aperture     SWP46933HIGHLARGE
   3   Object ID                       HD  55857
   4   RA  (1950)                      07:11:35
   5   DEC (1950)                      -27:16:09
   6   IUE Object Class                20
   7   Trailed flag                    NO-TRAIL
   8   Segmented exposure flag         NO
   9   Exposure time (seconds)         149.784
  10   Observation date dd/mm/yy       13/02/93
  11   Observation time (UT)           20:03:49
  12   Observation day of year         44
  13   THDA at start of exposure       9.51
  14   Processing date dd/mm/yy        26/10/96
  15   Processing station              GSFC
  16   JD of observation               2449032.33598
  17   Estimated max continuum in DN   177
  18   Mean background in DN           35
  19   Formula for wavelength scale    w(k) = 0.05*k +1150, k = 0, 16499 (SWP) or 
                                       w(k) = 0.10*k +1900, k = 0, 12249 (LWP and LWR)

These are followed immediately by 3 columns of numbers. There are 16500 or 12250 (for short or long wavelength spectra) rows for the SWP files. The format of each row is 3e10.2, e.g., 

  1.55e-09  6.89e-10 -6.68e-10
  1.23e-09  4.57e-10 -6.69e-10
  9.77e-10  6.16e-10 -6.70e-10
  1.07e-09  4.44e-10 -6.72e-10
  4.87e-10  4.30e-10 -6.72e-10
  1.45e-09  6.40e-10 -6.74e-10

These columns are: 

     Quantity                    Units
     ^^^^^^^^                    ^^^^^
     flux*                       erg cm-2 sec-1 Å-1
     estimated noise             erg cm-2 sec-1 Å-1
     background level            erg cm-2 sec-1 Å-1
*An entry of -1 implies that all the data quality (i.e., nu) flags for the data used to produce the point were < -512.

[ADF] The IUE browse files were conceived and originally implemented by Dr. Derck Massa, Dr. Nancy Oliversen, and Ms. Patricia Lawton, then members of the GSFC Astrophyics Data Facility (ADF) staff under direction of Dr. Michael Van Steenberg. Some modifications have been made as part of the transition to MAST maintenance.