Supported Software: APEX
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Purpose and Description
The software in this package performs "multiframe" and "single frame" point source extraction. For multiframe point source extraction, the individual images from an input list are interpolated and coadded. Point source detection is performed on the coadded images. The main components of point source detection are linear matched filtering and image segmentation. It produces a detection list with the potential point sources' position estimates. Point source estimation is performed by Point-Response Function (PRF) fitting of the potential point sources from the detection list. The fitting is performed simultaneously in all the input images.
For single-frame point source extraction, the detection and extraction are performed on a single input image. Perl script apex.pl runs all the modules involved in multiframe point source extraction which includes image interpolation and coaddition. Perl script apex_1frame.pl runs the modules involved in single frame point source extraction. The input images have to be in FITS format.
There are no limitations on the pixel size of the mosaic. It can be made as small as desirable. The only limitation on the size of the mosaic is the requirement that the final mosaic cannot span more then a hemisphere, since the only two projections implemented so far are TAN and SIN. If interest exists, other projections can be implemented as well.
The following keywords are required in the headers of the input file for the software to work: BITPIX, NAXIS, NAXIS1, NAXIS2, CRVAL1, CRVAL2, CRPIX1, CRPIX2, CTYPE1, CTYPE2, and the CD matrix keywords CD1_1, CD1_2, CD2_1, and CD2_2.
The software will also work with the scale and rotation keywords CDELT1, CDELT2, and CROTA2 in place of the CD matrix keywords.
Downloading and Installing the Software
APEX is distributed as part of MOPEX.
Running APEX
A brief introduction on how to run APEX. Namelists for use with apex.pl and apex_1frame.pl can be found on the main MOPEX page.One script that users may find extremely useful is apex_qa.pl. This creates a residual mosaic after PRF-fitting of point sources. An example namelist can be found here.
Estimating the PRF
For APEX we use the the language common in the optics field, that the PSF is the point-spread function before sampling by the detector array, and the PRF is the point-response function that lists relative pixel values coming out of the array. These are explained in detail in PRF vs. PSF (pdf file). The following guide will help you create a PRF from a PSF.
An example of how to run PRF estimate, APEX, and obtain a residual image. Warning - do not use the MOPEX script prf_estimate.pl with IRAC data or any other data that are undersampled or display intra-pixel variability.
Description of Modules
| APEX Modules | Single Frame APEX Modules |
Documentation
Supporting Documentation
- How do you make the PRF from the PSF?
- PRF vs. PSF
- Note that the Data Handbooks (IRAC and MIPS) have sample namelists corresponding to specific examples discussed there.
- Also see the Main Documentation Page for additional documents.
