MOPEX User's Guide - IRSA

MOPEX User’s Guide
In order to fit the data, a modified Simplex algorithm is employed. The Simplex algorithm
does not use derivatives of the functions involved in minimization. This is a desirable feature
since the transformation from local coordinates to global coordinates can be a very
complicated function of its arguments.
In some cases, the PRF of a point source is not constant across all parts of the detector array.
APEX allows users to use a variable PRF by creating and specifying a PRF map. The PRF
map is a file that splits the array up into areas of constant PRF, so that a single PRF image
can be used for sources that are detected within each area. A PRF map therefore identifies
areas of constant PRF, and matches each area to an individual PRF file that should be used
for point sources detected within that area.
The product of the Point Source Estimation stage is an extraction table that has over 20
columns, including point source positions in the sky and mosaic coordinates, fluxes,
positional and flux uncertainties, SNR, etc.
Aperture Photometry
For each extracted point source, aperture photometry can be calculated. The user can specify
an arbitrary number of aperture values. The results are appended to the output of the point
source estimation. The aperture photometry is calculated using an exact algorithm to compute
a fractional aperture-pixel overlap.
Figure 6.1 gives an overview of the APEX processing stages.
Point Source Extraction (APEX) 102
APEX Processing Stages