The MAST Spectral Data Coplot utility is designed to allow users
to coplot multiple spectra from the various spectral
missions/instruments supported by MAST. For HST instruments,
the plotted data is obtained from the preview files
produced by CADC. For the other MAST missions, the data
is extracted from the ASCII preview files. In both cases,
differences may exist between this data and that found in the
distributed FITS files.
The current list of spectral data sets to choose from includes:
STIS, IUE, EUVE, HUT, BEFS, TUES, FOS, GHRS, and WUPPE.
For Kepler, plots can be produced from the FITS
light curve files so the displayed data would be identical
to the distributed data.
Other mission data sets will be ignored.
A capabililty has been added to compute the mean of "like"
spectra and display the result. See the explanation for this at
the bottom of this page.
Enter the name(s) of the data set to be plotted,
star5ting with the first "data set name" input box.
The name must be specified in the format in which
the data has been archived within MAST.
Example data set names include:
EUVE: 3c273_178d_sum, au_mic__9207141227N
TUES: tues4201_7_1, tues2285_1
WUPPE: sk69-239_451611_2, psi-per_220510_2
Case should not matter, although
entering names in a different format (e.g., leaving a space
between swp and 16877), will prevent the
program from reading the files. Enter up to 15
data set names in the provided boxes.
The spectra or times series data you selected will be automatically scaled to
the full range of values along the X-axis. Spectral fluxes will scale
from 0 (or .25 * the minimum flux
for spectra with negative fluxes) to the 10th highest flux).
Light curve fluxes simply scale from the minimum to the maximum value.
Each plot is
automatically assigned a color, up to a maximum of 15, and
labelled by their dataset names followed by a ":" and
the applied scale factor. A summary of the
datasets is given below the plot. After inspecting the plot,
you may wish to change the selection of datasets which are displayed.
Use your browser "Back" button to do this.
Adjust the minimum and maximum X-axis and/or flux values
in the displayed units to select
the spectral region of interest and to exclude noisy data.
Adjust the X size and Y size in
pixels to create the size of plot desired. The maximum dimensions
are 850 by 640 pixels.
Each spectrum can be individually scaled by entering
a scale factor in the box next to the appropriate data set name,
and then redrawing the plot. The new scale factor should be seen
both in the scale factor input box, and following the data set
name in the upper right corner of the displayed plot.
Use this button to replot the spectra when you
have changed any of the plot parameters.
Two buttons have been added to plot just the average of like
spectra or to coplot this average along with the constituent spectra.
In both cases the mean spectrum is labeled "Average spectrum" and
plotted in black.
The averaging option works only for "like" spectra
The averaging option keys on the total number of points represented in the
first (primary) spectrum (irrespective of the wavelength limits entered).
The averaging option of the Coplotter is a "dumb" feature, meaning that
it can be used only to compute averages from spectral files having the same
number of total points, i.e. spectra observed in a common instrumental
configuration. For example, an LWP or LWR IUE
spectrum cannot be coaveraged with an IUE SWP spectrum (or a HST/GHRS
spectrum with another GHRS spectrum observed with a different grating).
If a secondary spectrum is added which fails this equality-of-points test,
the secondary will be overplotted but not coaveraged. Garbage in, garbage out!
The averaged spectrum is a straight mean of the input flux vectors. One
exception is that for IUE data pixels with flags less than -512 are
assigned zero weights; those data are not averaged in the plot (even
if corresponding pixels from other spectra in the coaddition have good