Events during an ICE CCD exposure

ICE (the IRAF Control Environment) is used at the telescopes on Kitt Peak (and elsewhere) to acquire CCD exposures.
The exact sequence of events during a CCD camera exposure is laid out below.

1. Prompt the observer for task parameters.

2. Update the filter and focus parameters to be passed to the (telescope) server.

3. Prompt the observer for the image title and retrieve hidden parameters.

4. Construct the name for the output image.
   • abort if it already exists
   • print a message otherwise

5. Open a connection to the detector server.
   • pass info back and forth to the controller,
   • retrieve the detcap information,
   • complain about the head ID if it does not match
   • check the error status

6. Update the scan table parameters to be passed to the instrument server (if appropriate).

7. Open a connection to the instrument server (usually "test").
   • pass info back and forth,
   • check the error status

8. Open a connection to the telescope server.
   • pass info back and forth (e.g. image header info),
   • check the error status, but ignore any error if this is not an object exposure

9. If no errors have been reported by the servers:
   • do whatever the instrument does before the exposure, e.g., position the scan table if appropriate
   • check the error status

10. If no errors have been reported by the servers (including the telescope):
    • do whatever the telescope does before the exposure, e.g., position the focus and filter if appropriate
    • check the error status

11. If no errors have been reported by the servers:
    • assign a unique RECID to the exposure
    • preallocate disk space if appropriate; the observe task aborts if the disk fills up
    • write out the exposure status line
    • prepare the chip
    • if no new detector error, start the exposure; the count down loop is entered if the exposure is longer than a few seconds
    • if exposure is not aborted, read out the chip:
      • open the output image (or reopen if preallocated)
      • write the header
        • most keywords were filled in previously
        • get a few (e.g., filter) from the servers now that were set after the bulk of the header info was retrieved
      • print "reading out..." message
      • initiate ccd data transfer
      • complain if there is a problem
      • close the output image
      • rename the hidden image if preallocated
      • complain if the disk would fill up

12. Close the detector, instrument and telescope servers.

13. Null out the motor control parameters for the filter, focus, and scan table.

14. If no errors were reported by the servers and the exposure was not aborted, execute the postprocessing command.
    • beep the terminal
    • display the image
    • if not a test image:
      • retrieve the RECID from the header
      • write a fits file named RECID to the /bits spool directory
      • send this to the archive queue using lpr
      • lpr removes the fits file afterward
      • update the local archive log with the pathname, RECID, and date
      • perform any observer edited chores

15. That's all folks!

Rob Seaman