Setting the calibration source model

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Setting the calibration source model

When solving for a visibility-plane calibration component, the Calibrater tool requires that the calibrator model be set first. This is stored in the MODEL_DATA column, and used by the Calibrater tool to form $\chi^{2}_{}$ when solving for calibration components. In general, this process requires transforming a source model from the image-plane to the visibility-plane, including any image-plane calibration effects. For this reason, the AIPS++ functions for converting source models to the visibility plane are attached to the Imager tool.

For the ATCA, the default source model is usually either 1934638 or point sources of unit flux density. If you have used 0823500 as your primary calibrator, or given 1934638 another name, you'll need to set the flux density for it by hand (see below).

To compute source models of this type:

imagr:= imager('atca.ms');         # Create an imager tool
imagr.setjy(fieldid=1);            # Compute source model for primary calibrator OR
imagr.setjy(fieldid=1,spwid=1,fluxdensity=5.6);    # Set flux density explicitly for source
imagr.setjy(fieldid=1,spwid=2,fluxdensity=5.8); 
imagr.done()

In these examples, the source is specified through its fieldid argument. Running the Imager.setjy function without arguments will compute the default point source flux density for all recognized standard sources for all spectral windows in the data. The Imager.setjy function also allows selection by field id. and spectral window id. as required, as well as the specification of an arbitrary Stokes (I, Q, U, V) for individual sources where necessary. The standard sources recognized are [(3C286, 1328+307, 1331+305), (3C48, 0134+329, 0137+331), (3C147, 0538+498, 0542+498), (3C138, 0518+165, 0521+166), (1934-638), and (3C295, 1409+524, 1411+522)]. At the present time, the flux density is computed for the frequency mid-point of each spectral window using the Perley-Taylor (1995) spectral index coefficients by default. All unrecognized sources, will be set to unit Stokes I flux density. (Note that the MODEL_DATA for all sources is already set to unity when this column if first created, so you don't normally need to do this again here.)

Arbitrary source models can be set using the Imager.ft method, which will transform images and source model components, as required.

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