5.2 Input parameters

Where to start ?

The script for automatic photometry is contained in the file “05_photometry\photosearch_run.py”. To execute the script, just edit the file, modify the input parameters, save the updated file and execute the script by double-click on the file icon in Windows.

The following 5 input parameters must be provided:

  • the names of the input images
  • the number of stars to be detected and measured
  • the number of reference stars
  • the sizes of the disks for photometry
  • a generic name to be used to create the output files

Names of the input images

The input images must be provided in a list, exactly as for the script for accurate photometry:

Imagelist = ['C:\\image1.fit', 'C:\\image2.fit', 'C:\\image3.fit']

For more details, you can have a look here.

Number of stars

The user specifies how many stars he would like to measure (say N). The script will detect automatically the N brightest stars in the image. Of course is N is larger than the actual number of stars, the script will detect noise fluctuations instead of stars. At the beginning of the script execution, the user has the possibility to visualise the detected stars, and to make sure that an appropriate number was specified:

nbtarget = 2000

The user also needs to specify the number of reference stars he would like to use, to calculate differential magnitudes:

nbref = 20

Disk sizes for photometry

To do aperture photometry we need to specify 3 different disk sizes:

  • the first size is the radius (in pixels) of the internal disk : all the pixel inside this disk are summed to get the star signal
  • the second and third size correspond to the internal and external radii (in pixels) of a ring. The median value of all pixels inside this ring corresponds to the sky background

At the moment one single set of such photometry disks must be specified:

sizes = [[3,8,40]]

If several set of disk sizes are specified then only the first one is used, so that:

sizes = [[2,8,40],[2.5,8,40],[3,8,40],[3.5,8,40],[4,8,40],[4.5,8,40],[5,8,40]]


sizes = [[2,8,40]]

are equivalent. A future version of the script may use several sets of disk sizes to identify the false star detections.

Generic name for output files

Finally, the user must provide a generic name that will be used to create the names of the output files. For instance, if the user provides:

generic_name = 'C:\\Desktop\\24Jan2010\\ProcessedImages\\Target-'

Then the output files will have the following names:

  • C:\Desktop\24Jan2010\ProcessedImages\Target-01_check_images.txt
  • C:\Desktop\24Jan2010\ProcessedImages\Target-02_image_shifts.txt
  • C:\Desktop\24Jan2010\ProcessedImages\Target-03_magnitudes.txt