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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