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polcalc stsdas.hst_calib.fos.spec_polar



polcalc -- Calculate polarization from Stokes IQUV spectra.


polcalc input output


The polcalc task recomputes polarization spectra (linear, circular, and position angle) from the Stokes IQUV parameter spectra in an FOS polarimetry (c3h) file. This allows a user to manipulate or modify the Stokes parameter spectra in a c3h file in any desired way and then recompute the polarization spectra from the modified Stokes spectra.

All four sets of Stokes and polarimetry spectra within the input c3h file (corresponding to instrument pass direction 1, pass direction 2, 1+2 combined, and 1+2 combined and corrected) are operated on by this task. The output file (in standard c3h format) is a copy of the input file with the data groups corresponding to the polarization spectra (9-14, 23-28, 37-42, and 51-56) replaced by their new values.

The formulae used to compute linear (PL) and circular (PC) polarization, polarization position angle (THETA), and their errors from the Stokes IQUV spectra are identical to those used in the calfos, calpolar, polave, and polbin tasks. Note that these algorithms assume that the Stokes QUV spectra in the input c3h file have NOT previously been normalized by Stokes I. See the help page for the polbin task for a listing of these formulae.


input [file name]
Input polarization (c3h) file name. If the input file name extension is not given explicity, an extension of c3h is assumed.
output [file name]
Output file name. If the output file name extension is not given, an extension of c3h is used.
(verbose = yes) [boolean]
Print operations as they are performed?


1. Recompute the polarization spectra from the Stokes parameters in the file y0xr0305t.c3h, storing the output in y0xr0305_new.c3h.

   sp> polcalc y0xr0305t.c3h y0xr0305_new.c3h


At this time this task does NOT incorporate the appropriate corrections for post-COSTAR FOS spectropolarimetry data.


Author: Howard Bushouse, STSDAS


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


plbias, polave, polbin, polnorm

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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