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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 23Immediately 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.
| 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 |
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.
| 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.
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.
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