Basic Information on uvfit

Task: uvfit
Purpose: Fit point sources to a given vis file.
Categories: uv analysis

        UVFIT is a Miriad task which fits model components to a visibility
        dataset. Optionally the model or residual visibilities can
        be written out.

Key: vis
        Name of the input visibility file. No default.

Key: stokes
        Normal Stokes/polarisation parameter (e.g. i,q,u,v,ii etc).
        Only a single polarisation can be requested. The default is
        `ii' (i.e. Stokes-I for an unpolarised source).

Key: line
        Normal line-type processing with normal defaults.

Key: select
        Normal data selection. Default is all cross-correlation data.

Key: object
        This gives the object type that uvfit fits for. Several objects
        can be given (the objects can be of the same type, or different),
        and minimum match is supported. Possible objects are
          point       A point source
          disk        An elliptical or circular disk.
          gaussian    An elliptical or circular gaussian.
          shell       The 2D projection of a thin, spherical shell.
          ring        A face-on, thin, elliptical or circular ring
        For example, to fit for a point source and gaussian, use:
        `object=point,gaussian'.

Key: spar
        This gives initial estimates of source parameters.  For
        each object given by the `object' keyword, either 3 (for
        point sources) or 6 (for disks and gaussians) values should be
        given. The values are as follows:
          Object Type             SPAR values
          -----------             -----------
           point                   flux,x,y
           gaussian                flux,x,y,bmaj,bmin,pa
           disk                    flux,x,y,bmaj,bmin,pa
           shell                   flux,x,y,bmaj
           ring                    flux,x,y,bmaj,bmin,pa
 
        Here "flux" is the total flux density of the component,
        "x" and "y" are the offset positions (in arcsec) of the object
        relative to the observing center, "bmaj" and "bmin" are the major
        and minor axes FWHM (in arcsec), and "pa" is the position angle
        of an elliptical component (in degrees). The position angle is
        measured from north through east.
        You must give initial estimates for all parameters for each object
        (this includes parameters that are redundant or meaningless,
        such as "bmin" and "pa" for components that are constrained to be
        circular).
 
        The more complex the set of objects being fitted for, the more
        important it is to give a good estimate of the source parameters.
        Generally the estimates of the source position should be accurate
        to the fundamental resolution (for point sources) or the size of
        the component (for extended sources).

Key: bin
        Specify frequency and time binning of the data.
        The first value specifies the size of the frequency bins in GHz
        to divide the data into.
        The second value specifies the size of the time bins in hours.
        An initial fit with all the data will be done to improve the
        starting values of the fit.
        The output will contain the interpolated model (or residuals).
        A spectral index estimate will be given for frequency binning.
        Defaults to 0,0 (no binning).

Key: fix
        This gives a set a flag parameters, one parameter per source.
        Each parameter consists of a set of letters, which indicate
        which source parameters of a component are to be held fixed.
        These source parameters are fixed by the initial estimates
        given by the `spar' parameter.
        The letters corresponding to each source parameter are:
          f   The flux is fixed.
          x   The offset in RA is fixed.
          y   The offset in DEC is fixed.
          a   The major axis parameter is fixed.
          b   The minor axis parameter is fixed.
          p   The position angle parameter is fixed.
          c   The gaussian, disk or ring is circular (not elliptical).
        For a source where all source parameters vary, a dash (-)
        can be used for this parameter.
 
        For example "fix=fx,fc" indicates that the flux and RA offset
        is to be fixed for the first source, whereas the second source,
        (which is presumably a gaussian, disk or ring) has a fixed flux, and
        is circular

Key: fix2
        Like fix, but applied after the initial fit using all data.
        Use this with the bin parameter to fix e.g., position while
        fitting for flux variation with time or frequency.
        Defaults to the value of fix.

Key: out
        Optionally, you can specify one or more output files for model
        or residual visibilities. If you specify one output file, all data
        will be written to that file. If you specify more than one output
        file, the number of output files should equal the number of input
        visibility files.

Key: options
        Extra processing options. Several can be given, separated by commas.
        Minimum match is used. Possible values are:
          residual The output data-set is the residual visibilities.
                   If an output is being created, the default is to make
                   this the fitted model.
 
 
Revision: 1.10, 2013/08/30 01:49:21 UTC