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Basic Information on mfspin
Task: mfspin
Purpose: Compute spectral index from a MFCLEAN model.
Categories: deconvolution
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.
Key: model
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).
Key: beam
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.
Key: clip
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.
Key: fwhm
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.
Key: pa
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).
Key: options
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.
Key: out
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).