IV. 2MASS Data Processing

5. Extended Source Identification and Photometry

a. Algorithms, Analysis and Results

ii. 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 affected by this modification, since they are allowed to shrink to radii near the PSF.

An example of a dynamically adjusted axis ratio is shown in Figure 1. The nominal axis ratio is 0.4, and the position angle is -45°. Note the increasingly circular aperture, as the radius approaches the size of the PSF.

Figure 1

[Last Updated: 2002 Jul 15; by T. Jarrett]

Return to Section IV.5a.