The package has a number of programs that can be
used to make the photometry of a list of objects. Basically the photometry
is done by fittng a PSF model to a fixed position in the subtracted image.
This PSF model is generated by convolving with the kernel solution a model
of the PSF in the reference image. The reference image can be divided in
a number of areas (as for subtraction), and within each of these area a
PSF model is constructed by median stacking of bright stars. The program
which build this PSF map for the reference is called Bphot.
The program which uses this PSF map and convolves it with the local kernel
is called Cphot.
This program calculates also the magnitude by fitting the profile, and
write the data to the light curve. All these programs, as well as
the image subtraction itself are managed by the shell script phot.csh.
This script is in the sub-directory register of the distribution. Before
you can run this script, you need to edit the configuration file of the
photometric programs, which name is phot_config.
The most important parameter in phot_config the photometric
radius, radphot. All the pixels within a distance
radphot of the center of the object will be used to estimate the flux of
the object by fitting the model of PSF. The other parameters do not need
to be changed most of the time, or only changed slightly. Anyway be careful
to setup the saturation parameter properly.
Before you run phot.csh, you must get accurate coordinates for the objects you want to make photometry. The program "stack" you already used to build the reference frame can do that for you. Just provide the program with a crude estimate of the coordinate in phot.data, and the program will return accurate coordinates. First you need to create a "temp.data" file which will contain the coordinates of the objects for which you want to have photometry.An example of such file format is:
Xi and Yi are the coordinates of the maximum pixel
of the object (integer coordinates). If you
don't kow exactly what the coordinates of the maximum are, you can give
approximate coordinates, and the program will find the nearest local maximum.
You should then generate a few subtracted image in which your object has
large flux variations from the reference, stack these images and get the
position of your object. Note that
../bin/stack <image list> -o <ref name> -i temp.data
The default output file is "phot.data", you need this file to do the photometry. Check phot.data, it should look like that:
150.134 150.245 150 150 lc0.data
X and Y are the accurate coordinates of the object and Xi and Yi are the coordinates of its maximum. File will be the name of the file containing the light curve of this object.
Do not forget to indicate the name of the reference file
you want to use in the process_config file.
Once you are done, you can run the photometry package, just type:
If it does not work, or does not do what you expect,
first check that your file "process_config" is correct, and does contains
the name of all the necessary files.