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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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