### 6 Automated photometry

PHOTOM provides two methods to perform the photometry of objects in a non-interactive fashion. There are typically two reasons why you would want to do this:

(1)
There are far too many objects on your images, so a statistical approach with some measurements in error is a necessity.
(2)
You just want to use PHOTOM as an engine for other interactive or script based tools.

The second case is covered by the program AUTOPHOTOM, which is used by the photometry mode in the GAIA (SUN/214) image display tool. The first case by the PHOTOM program in a special mode.

You can use PHOTOM in ‘batch’ mode either interactively or by controlling it from an ICL command procedure or from a C-shell script. If you use a script of some kind then you’ll also need another file that contains the commands you would have used interactively. It may be necessary to run the program by hand first to verify the order of the prompts. An example input file (photom.in say) could contain the following commands:

FRAME
N
5.0
0.0
0.0
F
POSITIONS.DAT
E

In this example the image data is assumed to be in a file FRAME in the default directory. The size and shape of the aperture is set using the non-interactive command, N and the command F instructs the program to take the initial positions from the file POSITIONS.DAT. The E command ends the program.

The program could then be run in the background with the command

% photom < photom.in > photom.out &

Using AUTOPHOTOM requires that a file with a specified format is created, the details of which are described in in appendix 0. Basically this describes each aperture and also allows information about the sky region associated with it to be given. The sky region can be defined in a single annulus (each aperture can have a different inner and outer scale) or can be defined as a series of other apertures. The easiest way to create such a description of the apertures on an image is to use the GAIA display tool. This description can then be run on other frames non-interactively (say for different colours, or repeat measurements).