iraf.net

NUMBER:	131
MODULE:	artdata.mkobjects
SYSTEM:	V2.9
DATE:	Mon Jul 23 10:53:43 MST 1990
FROM:	valdes

BUG:	The moffat function size scaling (as set by the radius parameter)
	is incorrect.

STATUS: The shape of the function is based on the correct beta but the size
	is scaled for a function with beta of:
	
		beta1 = 2 * beta - 2

	Another way to look at it is that the flux level corresonding to
	the specified radius is different than the half intensity.  The
	actual flux level is:

		F(radius) = 0.5 ** (beta / beta1)

	Finally, the radius which must be specified, rfudge, to get a
	desired radius at half intensity, rhalf, is:

		rfudge = rhalf * sqrt ((2**(1/beta1)-1) / (2**(1/beta)-1))

	Note that there is no error for beta=2, the size is too large
	for beta>2, and the size is too small for beta<2.

	The workaround is to adjust the specified radius for a desired
	radius at half intensity using the above formula.