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 ringFor example, to fit for a point source and gaussian, use: `object=point,gaussian'.
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).
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.
residual The output data-set is the residual visibilities. If an output is being created, the default is to make this the fitted model.