Basic Information on mfspin

Task: mfspin
Purpose: Compute spectral index from a MFCLEAN model.
Categories: deconvolution

        MFSPIN is a MIRIAD task that 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 can also handle 'pre-convolved' images with flux and flux
        times spectral index planes such as those produced by restor
        with options=mfs or linmos with options=alpha.
 
        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). If the input already has
        units of 'JY/BEAM' (e.g. output from restor with options=mfs)
        the convolution step is skipped.
 

Key: beam
        The input dirty beam.  This is only required to determine the
        beam size.  If the fwhm parameter is given, or the input is
        already convolved, 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.

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).
 
Revision: 1.12, 2021/06/02 04:45:09 UTC