Axis Ratio and Small Radii

For small radii, we adjust the axis ratio such that the minimum semi-minor axis is 3 arcsec. This modification is needed to counteract the circularizing effects of the PSF. The half-light "effective" aperture and Kron aperture are particularly effected by this modification since they are allowed to shrink to radii near the PSF.

An example of a dynamically adjusted axis ratio is given below. The nominal axis ratio is 0.4 and the position angle is -45 degrees. Note the increasing circular aperture as the radius approaches the size of the PSF.

[Last Updated: 2002 Jul 15; by Tom Jarrett]