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polplot stsdas.hst_calib.fos.spec_polar



polplot -- Plot FOS polarimetry spectra as a stacked plot.


polplot image


This routine reads spectra from an FOS polarimetry (c3h) image and produces a stacked plot containing Stokes I (total flux) and either Stokes QUV or linear, circular, and position angle polarization spectra. Any one of the four sets of spectra contained within the c3h file may be plotted, where the first set corresponds to pass direction 1, the second to pass direction 2, the third to the combined data from both pass directions, and the fourth to the combined and instrumentally-corrected data.

The Stokes I (flux) spectrum is always plotted as a continuous line, while the user has the option of plotting the remaining Stokes or polarization spectra in one of three modes (set by the parameter ptype): individual points, continuous line, or histogram. Error bars for the Stokes QUV or polarization spectra may also be overplotted. Individual data points with error values equal to zero will not be plotted when using either the point or continuous line plotting modes (i.e. the "continuous" line mode will not be truely continuous, but will have gaps at the locations of bad points).

The user chooses whether to plot Stokes QUV or polarization spectra by setting the parameter spectra. If spectra = stokes, the Stokes QUV spectra will be plotted along with Stokes I; if spectra = polar, linear (PL) and circular (PC) polarization and polarization position angle (THETA) spectra will be plotted with Stokes I. Linear and circular polarization spectra are plotted in units of percent polarization and polarization position angle is plotted in units of degrees. The user also has control over whether or not to include Stokes V or circular polarization in the plot by setting the parameter circpol to "yes" or "no".

The x-axis of the plot may be displayed in units of either increasing wavelength (Angstroms) or decreasing inverse wavelength (10**4/Angstroms). A null value for the wavelength image name will cause the routine to search for a wavelength image with the same root name as the spectral data image, but with an image name extension of c0h. The spectral and wavelength images must have the same number of pixels per spectrum. The wavelength vector contained in data group 1 will be used for plotting spectral sets 1, 3, and 4, while wavelength image group 2 will be used when plotting spectral set number 2.


image [file name]
Polarization (c3h) image name. The image must be in FOS c3h file format. If no image name extension is given, an extension of c3h is assumed.
(set = 4) [integer, min=1, max=4]
Index of the spectral data set to plot:
1 = Pass direction 1                           (c3h groups  1-14)
2 = Pass direction 2                           (c3h groups 15-28)
3 = Pass directions 1+2 combined               (c3h groups 29-42)
4 = Pass directions 1+2 combined and corrected (c3h groups 43-56)
(spectra = "polar") [string, allowed values: polar | stokes]
Plot polarimetry spectra (linear, circular, and position angle) or Stokes QUV parameter spectra?
(wave = "") [file name]
Wavelength image name. If null, the task will search for an image with the same root file name as the polarization (c3h) image, but with an extension of c0h. If the image name extension is not given, an extension of c0h is assumed.
(invlam = no) [boolean]
X-axis plotting units. If "no", then plot increasing wavelength; if "yes", plot decreasing 1/wavelength.
(errors = yes) [boolean]
Overplot error bars on Stokes QUV or polarization spectra?
(ptype = "c") [string, allowed values: c | h | p]
Type of plotting mode to use when plotting Stokes QUV or polarization spectra: c[ontinuous] line mode, h[istogram] mode, or p[oint] mode.
(circpol = no) [boolean]
Include Stokes V (if spectra = stokes) or circular polarization (if spectra = polar) in plot?
(wmin = 0) [real]
Left limit for plot x-axis (wavelength or 1/wavelength). If wmin = 0, start at first pixel.
(wmax = 0) [real]
Right limit for plot x-axis (wavelength or 1/wavelength). If wmin = wmax, the entire wavelength range of the data will be plotted.
(imin = 0) [real]
Lower limit for Stokes I (total flux) plot.
(imax = 0) [real]
Upper limit for Stokes I (total flux) plot. Autoscale if imin = imax.
(cmin = 0) [real]
Lower limit for circular polarization plot (in percent). If plotting Stokes spectra this corresponds to the Stokes V parameter plot.
(cmax = 0) [real]
Upper limit for circular polarization (or Stokes V) plot (in percent). Autoscale if cmin = cmax.
(lmin = 0) [real]
Lower limit for linear polarization plot (in percent). If plotting Stokes spectra this corresponds to the Stokes Q parameter plot.
(lmax = 0) [real]
Upper limit for linear polarization (or Stokes Q) plot (in percent). Autoscale if lmin = lmax.
(pamin = 0) [real]
Lower limit for polarization position angle plot (in degrees). If plotting Stokes spectra this corresponds to the Stokes U parameter plot.
(pamax = 0) [real]
Upper limit for polarization position angle (or Stokes U) plot (in degrees). Autoscale if pamin = pamax.
(title = "imtitle") [string]
Title to be centered above the plot. The user can specify a title string; the default string is the image name and title.
(device = "stdgraph") [string]
Plot device.


1. Plot the total flux (Stokes I), the linear polarization, and the polarization position angle spectra, along with their errors, from the 4th set of spectra in file y15v0403t.c3h, with wavelengths from file y15v0403t.c0h. Only plot points between 2600 and 3000 Angstroms and allow autoscaling of all spectra.

   sp> polplot y15v0403t.c3h 4 wmin=2600 wmax=3000

2. Plot the same data as above, but limit the x-axis of the plot to inverse wavelengths between 4.0 and 3.5 inverse microns. Set the scaling for the flux plot from 3.e-14 to 5.e-14 (ergs/sec/cm**2/A), the linear polarization plot from -0.1 to 2.3 percent, and the polarization position angle plot from -45 to +75 degrees. Include a title and send to a hardcopy device.

   sp> polplot y15v0403t.c3h 4 invlam+ wmin=4.0 wmax=3.5 \
       >>> imin=3.e-14 imax=5.e-14 lmin=-0.1 lmax=2.3 pamin=-45 \
       >>> pamax=75 title="Mrk 421" device=stdplot

3. Plot rebinned Stokes IQUV spectra from image mrk421_rebin.c3h, taking the wavelength array from mrk421_rebin.c0h. Plot the data from set number 2 (corresponding to pass direction 2) of the c3h image, with the QUV spectra plotted in histogram mode with no error bars.

   sp> polplot mrk421_rebin.c3h 2 spectra=stokes err- ptype=h circ+



Author: Howard Bushouse, STSDAS


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


polbin, grspec

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.

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