REFERENCES · HELP · SEE_ALSO

## NAME

comparesets -- Compare flux spectra at different waveplate positions.

## USAGE

`comparesets image pass_dir`

## DESCRIPTION

The `comparesets` task produces a stacked plot of the flux spectra at all
waveplate positions for an FOS polarimetry flux calibrated (`c1h`) data file
and also computes statistics for each of the individual spectra. This allows
for the identification of spectra at individual waveplate positions that may be
corrupted or of lower quality than other spectra. The dataset
can then be reprocessed using the `calpolar` task, excluding any bad waveplate
positions from the computations.

Only one of the two sets of spectra from the two orthogonal instrument pass
directions may be plotted at a time; the choice of which pass direction to
plot is set via the `pass_dir` parameter. The spectra may be plotted as is,
or the user can choose to ratio each spectrum against the spectrum
from a chosen reference waveplate position.

Statistics computed for the spectra at each waveplate position include the mean and standard deviation as measured over a chosen sample range. The statistics are written to the terminal screen in the following format:

# POS GROUP SAMPLE MEAN STDDEV 1 1 [start:end] x.xxxxxxx x.xxxxxxx 2 3 [start:end] x.xxxxxxx x.xxxxxxx 3 5 [start:end] x.xxxxxxx x.xxxxxxx 4 7 [start:end] x.xxxxxxx x.xxxxxxx

where "POS" gives the waveplate position number, "GROUP" is the data file group number of the spectrum, and "SAMPLE" gives the pixel range used to compute the mean and standard deviation.

## PARAMETERS

- image [file name]
- Input flux image name. If the input image name extension is not
given, an extension of
`c1h`is assumed.

- pass_dir [integer; min=1, max=2]
- The pass direction of the set of spectra to plot. The only allowed values are 1 or 2.

- (normalize = yes) [boolean]
- The normalize switch controls whether or not to normalize the spectra by
the spectrum at a chosen reference waveplate position (see
`refpos`). If set to "yes", all spectra will be divided by the spectrum at the reference position before plotting and calculating statistics. The reference spectrum itself is not included in the plot. If set to "no", all spectra are plotted in their natural form.

- (refpos = 1) [integer; min=1, max=16]
- The waveplate position of the spectrum to be used as a reference when
normalizing. If
`normalize = no`, this parameter is ignored.

- (wave = "") [file name]
- The wavelength image name. This file is used to provide a wavelength
scale for plotting the flux spectra. If the
`wave`parameter is left blank (the default), a wavelength file having the same root name as the input flux image and an extension of`c0h`is used. If a wavelength image name is given without an extension, an extension of`c0h`is assumed.If no wavelength image is found, the plot will be produced in pixel space. In this case, the statistics sample range (if one is given) must also be expressed in pixel space.

- (stats = yes) [boolean]
- Compute statistics for the spectra? If set to "yes", the mean and standard
deviation of each spectrum will be calculated over the sample range
specified by the
`sample`parameter (see below). The statistics are printed to the terminal screen.

- (sample = "*") [string]
- The sample range to use when computing statistics. If
`stats = no`, this parameter is ignored. The sample range is expressed as "start:end". If a wavelength image is used to provide a wavelength scale for the spectra, then the sample range must be given in terms of starting and ending wavelengths. If no wavelength scale is available, the sample range is given in pixels. The default value of "*" will use the entire range of the spectra.

- (wx= 0.) [real]
- Starting x-coord for plot. If a wavelength scale is provided, this value must be given in terms of wavelength, otherwise pixel space is used.

- (wx= 0.) [real]
- Ending x-coord for plot. If wx1 = wx2, the plot will be autoscaled in the x-axis to include the full x-range of the spectra.

- (wy= 0.) [real]
- Lower y-coord limit for plot.

- (wy= 0.) [real]
- Upper y-coord limit for plot. If wy1 = wy2, the plot will be autoscaled in the y-axis to include the full y-range of all spectra.

- (device = "stdgraph") [string]
- Output graphics device name.

## EXAMPLES

1. Plot the spectra for pass direction 1 in the image `y0nb0203t.c1h`. The
spectra at waveplate positions 2-8 will be ratioed against position 1 and
statistics will be computed over the full range of each spectrum. Wavelengths
are read from the file `y0nb0203t.c0h`. Both the x- and y-axes of the plot
will be autoscaled.

sp> comparesets y0nb0203t 1 # POS GROUP SAMPLE MEAN STDDEV 2 3 [ 1:2064] 1.052 1.022 3 5 [ 1:2064] 1.095 1.467 4 7 [ 1:2064] 1.129 1.038 5 9 [ 1:2064] 1.097 1.637 6 11 [ 1:2064] 1.047 1.472 7 13 [ 1:2064] 1.082 1.164 8 15 [ 1:2064] 1.123 1.026

2. Plot the spectra for pass direction 2 in the image `y0nb0203t.c1h` but
don't normalize them. Compute statistics over the wavelength range 1800
to 2000 Angstroms.

sp> comparesets y0nb0203t 2 norm- sample="1800:2000" # POS GROUP SAMPLE MEAN STDDEV 1 2 [ 631:1172] 2.098E-14 6.078E-15 2 4 [ 631:1172] 2.181E-14 6.093E-15 3 6 [ 631:1172] 2.098E-14 5.905E-15 4 8 [ 631:1172] 1.984E-14 5.611E-15 5 10 [ 631:1172] 2.118E-14 6.180E-15 6 12 [ 631:1172] 2.147E-14 5.974E-15 7 14 [ 631:1172] 2.103E-14 5.830E-15 8 16 [ 631:1172] 2.001E-14 6.138E-15

## BUGS

## REFERENCES

Author: Howard Bushouse, STSDAS

## HELP

For assistance using this or any other tasks, please contact help@stsci.edu or call the help desk at 410-338-1082.

## SEE ALSO

Type "help spec_polar opt=sys" for a tutorial on FOS polarimetry datasets and the use of the spec_polar tasks in a coordinated fashion.