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Photometry code

The algorithms are implemented in the module opt_extr.f90, for which you will also need Koji Mukai's implementation of the Marquardt algorithm, marq.f90. You may like to see how I've used opt_extr in my own program for time series work, called opphot.f90. Since opphot is an ARK program, you won't be able to link it unless you install all the stuff given below, but it is a good model for how the calls work. It refers to a Fortran 90 structure called a_star, which is described in define_star.f90 If you want to test your version of the code there is some sample data in FITS format called image1.fts and image2.fts You will also need the files psf.cat, stars.cat, and offsets.dat. If you use those names, you can then run opphot using the default answers to the prompts, except that you will need to type "end" to the requests for the file of frame times, type 5 for any search radius, and when you are asked which star to optimise for, give -1, which is the sky optimisation. This will then give you photometry in the files star01.opt, star02.opt and star03.opt, that you can compare with those provided here. For time series work this is not the final answer, of course, you must re-run the code with fixed positions for the stars. These are provided in stars.pos_new. You may also find the user documentation for opphot useful.

Opphot requires accurate offsets between each image in the time series, which can be obtained from a program originally written by Robin Corbet called mapccd.f90. For this program you'll also need blnclc.f90. Again you can test this using image1.fts and image2.fts, and giving the default values in answer to the prompts. This will create for you the same offsets.dat file which you used above for testing opphot. You may also find the user documentation for mapccd useful.

If you really want an off-the-shelf system for time series photometry, or want to play with the code, everything you need to compile it is here. Just unpack the tar ball and read the README file.

Finally, you can see Keele teach their undergraduates to use the code in ARK CookBook.

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