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The phot guide




To do windowed photometry it is necessary to know the precise positions of the target stars on the CCD detector. This is accomplished by first obtaining an image of the whole field (with tcpcom in normal full frame imaging mode), and making sure that the target and reference stars are present in the field. Starting phot will display this image (using the image display program saoimage and allow the user to mark the relevant targets and sky fields. When this is done the information about these windows are stored to two data files, and the program can be terminated.

Starting phot

  • Get a new xterm window from the left mouse button menu.
  • Change directory to the one where tcpcom stored the last data file. (The "Data directory" field in tcpcom page 0).
  • Start the phot script, i.e:

    > phot kd010001.fits

    Where "kd010001.fits" should be substituted with the filename of the last made image, that shows a full frame of the field that the telescope is currently pointing to.

  • There are no command line options to phot.
  • You should get a saoimage window that (after a while) will show the image of your field, scaled close to the background value to reveal all details.
  • If saoimage does not come up this is usually due to other applications reserving too many colors, leaving saoimage without enough color table entries, which it cannot handle. Press Ctrl-C to quit phot, and quit some non-terminal applications that are running on the display (particularly netscape!), then try again.
  • For on-line help, use the `?'-key.

Output files

The phot program produces two output files.
  • "photwins.dat", contains the coordinates and dimensions of the fields in the order selected by the user, assuming that the primary target is the first (channel #1), followed by one or more reference stars, and one or more sky fields at the end. This file is used to reconstruct the correct sequence during processing with rtp.
  • "photwccd.dat", contains the images sorted in the CCD readout direction, and with a bias level field added at the end. It is this second file that contains the information that tcpcom reads and transmits to the camera to initialise windowed readout.

Keystroke commands

The basic keystroke commands in phot are applied in the saoimage window, and are as follows:
  • The `s'-key places a square box around the image pointer.
  • The `d'-key attempts to delete any box around the pointer.
  • The `D'-key deletes all markers on the display.
  • The `R'-key redraws the image.
  • The `W'-key calculates the CCD window list and writes the output files.
  • The `q'-key quits phot.
  • The `?'-key prints a help page.
Additionally the `:'-key makes it provides a command line for changing the current settings. Hitting this key in saoimage moves the control to the terminal window where phot was invoked, and allows the typing of commands. The return key gets you back into saoimage. The only really useful command here is the "size" command. This allows you to change the size of the square box from 64 by 64 to any size.

Back to top Last modified: April 19 2023