Content-type: text/html Manpage of mfspin


Section: User Commands (1)
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mfspin - Compute spectral index from a MFCLEAN model.  






MFSPIN is a MIRIAD task which computes spectral index and possibly rotation measure images, given models produced by MFCLEAN. It does this by convolving both the flux and "flux time spectral index" planes of the models by a Gaussian, and then performing a division.

It has two modes of operation. One is to give a single input model (Stokes I or V even) which consists of two planes. MFSPIN will then compute the spectral index image from that. The second mode requires both Stokes Q and U models. MFSPIN will then compute a linearly polarized intensity spectral index and optionally a rotation measure image.  


The model produced by MFCLEAN. No default. Normally this will be a single image such as a model for Stokes I or V. However, you can also give it two models, one for Stokes Q and one for Stokes U (see the discussion above).
The input dirty beam. This is only required to determine the beam size. If the fwhm parameter is given, the beam will not be used.
The division clip level. One or two numbers can be given. If two values are given, then flux pixel values in this range are flagged as bad before the division (but after the convolution!). If a single value is given, then for Stokes I images (or images for which the Stokes parameter is unknown), all pixel values less than the specified clip are flagged. If one value is given and the image is of Stokes Q,U or V, then pixels are flagged when their absolute value is less than the clip level. The default is 0.
The size, in arcsec, of the gaussian beam to convolve with. This will normally be two numbers, giving the full-width at half-maximum of the major and minor axes of the gaussian. If only one number is given, the gaussian will have equal major and minor axes. If no values are given, they are computed by fitting a gaussian to the given dirty beam. Note that the fitting routine will probably give different values to the AIPS MX and APCLN tasks. Generally the value computed by MFSPIN is to be preferred to the APCLN and MX values.
The position angle, in degrees, of the gaussian, measured east from north. The default is determined from the dirty beam fit (The value for PA is ignored, if no value is given for FWHM).
Extra processing options. Several can be given, separated by commas. Minimum match is used. Possible options are:
  pbcorr   Correct the spectral index for primary beam effects.
           By default, this is not performed.
The output image names. No default. Normally this will be a single output, being the spectral index. If the input consists of a Q and a U model, the output can be two names. The first is the linearly polarized intensity spectral index image, and the second will receive an estimate of the rotation measure (units of rad/m**2).




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Time: 18:35:38 GMT, July 05, 2011