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6.1.1 Intensity Distributions

Several intensity distribution models are available (well, two). The parameters for these are usually passed as a Lua table in the optargs optional arguments parameter.

The intensity distribution may be specified independently in the X and Y directions, or may be specified as a common distribution. If no distribution is specified it will be uniform. Common parameters are provided via the the dist table, while parameters specific to an axis are provided via the x and y tables. This code

    disk( "disk", '40 arcminutes',
          {
            dist = { 
                     type = 'gaussian', 
                     sigma = '3 arcsec' 
                   },
            x = { center = '1 arcsec' },
            y = { center = '1 arcsec' }
          }  )

sets up a disk source with a radially symmetric Gaussian offset from the source center. Note that the center parameter is only valid in the axis specific tables. To specify independent distributions, don’t use the dist parameter:

    disk( "disk", '40 arcminutes',
          {
            x = { 
                     type = 'gaussian',
                     center = '1 arcsec',
                     sigma = '3 arcsec' 
                },
            y = { 
                     type = uniform'
                },
          }  )

The following distributions are available. The type of distribution is specified by the type parameter, as shown in the above examples.

uniform

This provides a constant intensity across the source. It has no parameters.

gaussian

This is a Gaussian distribution. The center is nominally at the center of the source, but may be changed. The width of the Gaussian is specified by one of the following two parameters:

fwhm

The Full Width Half Maximum of the Gaussian.

stddev

The standard deviation of the Gaussian.

The center of the Gaussian is specified via the center parameter, which must be specified independently for each axis.


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