Sextractor Cookbook

 "SExtractor" is a program that detects point sources in array images and catalogues their positions and fluxes together with other items of interest.

SExtractor uses several supporting files to parametrize its running conditions. It can run with or without the aid of a comparison file - a file which contains approximate positions of stars to select for centroiding. Two template versions of the configuration file are provided here in order to facilitate both kinds of operation.

1. Tune the configuration file for SExtractor Two versions of the file are available. Machine.config looks into a comparison file to determine where to look for point sources. Machine2.config searches over the whole image and can be used to generate an initial comparison file for further searches. Template copies of these are here:

It may be useful to rename ename these files something unique, or versions of SExtractor run simultaneously by multiple users will be confused! Example parameters that must be tuned: 2. Specify the output with the default.param file. Various categories of output from SExtractor are specified in the default.param file. Two template versions are given here: The difference between the two files centers on whether or not the results are with (default.param) or without (default2.param) the comparison file]

3. Use a batch file to run SExtractor on a series of files in a sub-directory.

"Runsex(2)" will iteratively run SExtractor in your subdirectory to create *.dat files of centroids for each image. These results can be used to create a "subdirectory.list" comparison file if needed.

Make sure that you are in one directory above the image file directory to run runsex, and that your versions of machine2.config, default2.param, sort, and runsex are in that directory.

4. Select a permanent set of reference stars. SExtractor output for each image will be written to *.dat files in the subdirectory. If you use the template default.param files, fluxes (in counts), X & Y of centroid, PSF rotation, elongation, ellipticity, and FWHM, and X & Y uncertainties will be written to the *.dat files. Use visual inspection of the image to interpret the results. Make sure that you have only high snr reference stars. When these are selected, incorporate them into a comparison file (starname.list) to be put into the working directory. Use this for all future centroiding for this target star.