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MX Browse Files

Welcome to the Multimission Archive at Space Telescope Science Institute (MAST). This page provides information on the IUE browse files; a collection of web pages accessible from both the IUE search page and as data links from the ADS. A separate MX (and SI) browse file is available for every IUE observation.

The main purpose of the MX browse files is to allow users to preview the IUE calibrated spectra. The spectra are displayed as plots of flux in ergs/cm2/sec/A versus wavelength in Angstroms, and are also available as downloadable ASCII table files. Differences between the low and high dispersion preview spectra are described below.

In addition to the plots and ASCII files, the browse files now include several additional items:

  • a list of useful information including the program ID principal investigator, proposal title, and selected FITS keywords describing the target and observation, (Note for most GSFC images, the program ID is linked to the observing proposal abstract in pdf format.)
  • a link to this help file,
  • a link to a page that allows users to customize the plot range and dimensions of data extracted from the ASCII table file,
  • a link to the corresponding spatially-resolved image (SI) browse file, (note: this is the file from which the fluxes were originally extracted and is particularly useful for detecting spurious features),
  • a link to download the NEWSIPS MX FITS file in tar format,
  • a link to download any of the NEWSIPS (or IUESIPS) data sets in a choice of tar, gzipped tar, or zip format,
  • a link to view the original hand-written IUE observing script (Goddard images only),
  • and a list of published papers referencing the particular IUE observation with links to the paper(s) available from the ADS (note however that not all papers are yet included in our database).

Details on Low Dispersion Spectra

If exposures were taken in both the large and small apertures, the low dispersion MX browse files will contain two sets of plots and ASCII files (note: small aperture data are not photometrically accurate although wavelength assignments may be more accurate). The plots display the original, unsmoothed fluxes > 0 although data points with Quality flags < -512 are not plotted. The table below shows the plotted wavelength coverage.

The gzipped ASCII files consist of an abbreviated header followed by the original, unsmoothed spectral data. (This includes negative fluxes and points with nu flags < -512 that were not included in the plot.) 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   Data ID + 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
Note if your browser automatically ungzips the file and displays it, you can still download the file by clicking on the "ASCII table" link using the right mouse button.

The wavelength coverage available, displayed on the plots and included in the gzipped ASCII files are listed in the table below.

Table 1: Low dispersion wavelength coverage
SWP LWP* LWR*
Wavelength coverage 1150-1978 Å 1851-3347 Å 1851-3348 Å
Wavelengths plotted 1150-1978 Å 1851-3200 Å 1851-3200 Å
Wavelengths in ASCII files 1150-1978 Å 1851-3347 Å 1851-3348 Å
*For the long wavelength cameras, data between 3200 and 3350 Å are not shown since the instrumental response and calibrations are not very good in this region.

Details on High Dispersion Spectra

The high dispersion plots show a 4-point binned version of a combined order spectrum which has been placed on a uniformly spaced wavelength grid with 0.05 Å spacing for the SWP spectra and 0.1 Å for the LWP and LWR spectra. Thus, the resolution of the plotted data (and the ASCII files) is either 0.2 or 0.4 Å. Points with quality flags < -512 are not plotted. Both the plots and the gzipped ASCII files are combined order echelle data. The spectra were created using IUEDAC software to combine most of the orders available in the MXHI files to form a single, continuous spectrum. Additional long wavelength coverage is available in the full MXHI FITS files but, because the echellograms were not centered on the IUE detector, there are large gaps in the coverage at these wavelengths and they are not included in either the preview plot or the gzipped ASCII files (see table below).

The gzipped ASCII files 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 has an entry of +1. Otherwise, the flags were ignored in the rebinning procedure. (Note: as in low dispersion, if your browser automatically ungzips the ASCII file and displays it, you can still download the file by clicking on the "ASCII table" link using the right mouse button.)

The contents of the ASCII file header are:

 Index Content                         Example
 ^^^^^^^^^^^^^                         ^^^^^^ 

   1   Disclaimer                      NOT ORIGINAL IUE PROJECT DATA PRODUCT
   2   Data ID + 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 in each file. 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.
**An entry of 1 implies all data quality flags were < -512 (same as flux=-1).

The complete and partial wavelength coverage available from the MXHI FITS files, and the wavelengths and orders displayed on the plots and included in the gzipped ASCII files, are listed in the table below.

Table 2: High dispersion wavelength coverage
SWP LWP LWR
Complete wavelength coverage 1150-1930 Å 1845-3105 Å 1845-3105 Å
Partial wavelength coverage 1930-2198 Å 3105-3230 Å 3105-3230 Å
Wavelength coverage shown 1150-1975 Å 1900-3125 Å 1900-3125 Å
Orders shown 70-120 74-121 74-121



Customize Plot Option

Both the low and high dispersion preview pages offer an option to customize and view a plot of flux vs wavelength, using data extracted from the ADF-produced ASCII table files. Unlike the preview image, "Bad" points, which were removed in the previews, are displayed here with values of 0.0. High dispersion data is displayed as a single plot. Besides displaying the mission name, target, aperture, dispersion, number of plotted points, and number of "bad" points (if any), the output page also displays the min and max wavelength and flux values of the extracted data.

The user can "customize" the plot parameters listed below. Note the process can be repeated multiple times until the right dimensions are determined.

  • Wavelength Limits - The minimum and maximum displayed wavelength can be specified by the user. Setting both values to 0.0 will allow the program to pick the best plot limits however, leaving one value as 0.0 will result in 0.0 being used as a plot limit.
  • Flux Limits - As with the wavelengths, the minimum and maximum displayed flux values can be specified by the user. This option is particularly useful for viewing continuum levels in spectra dominated by strong spectral features or camera artifacts.
  • Plot Dimensions - The user may adjust the X and Y dimensions of the displayed plot (in pixels) up to a maximum of 850 by 640 pixels.


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.