NB: The following discussion still holds - some more features however have recently been added. For a description of these added bits, see here.
The OFFSET_RUN file format was originally designed for
controlling IRIS (the AAT's infrared camera). It therefore allows control
of exposure parameters which are not relevant to CCD imaging -
specifically, the control of `CYCLES' and `PERIOD'. The parameters
you can control are
The OFFSET_RUN file is executed from the ICL terminal with the command
ICL> OFFSET_RUN filename
The default directory is DISK$RAW:[OBSERVER], and .DAT is the default file extension. DISK$RAW is specific to the VAX 4000, so you may find it more convenient to create the file on another disk.
This command initiates a sequence of runs. At each run the next line of the file is acted upon. This may involve offsetting the telescope, taking a dark exposure, or changing one of the other parameters. Runs continue until the end of the file. Note that you cannot alter the optical configuration or mode of taking data: these must be set before you begin.
A sample file follows. Each of the paremeters above is spcified by a single word - spaces are ignored, but DON'T USE TABS. Also, if you create it on some other directory ENSURE THAT IT HAS WORLD READ AND EXECUTE PROTECTION; failure to do so results in an error reporting "failure to open file".
! Sample offset run file
! Comment lines starting with `!' are ignored
!RUN/DARK OBJECT RAOFF DECOFF TRUE TIME CYCLE PERIOD REPEAT
! (") (") (s)
DARK dark 0 0 TRUE 0 1 1 1
RUN north 0 100 TRUE 40 1 1 1
RUN west -100 0 TRUE 40 1 1 2
This file will take a BIAS frame at the `base' position, then offset the telescope 100 arcsec north of base to take a 40 second exposure. Finally, two 40s runs are taken 100 arcsec west of base.
Things to note here are:
This telescope control mode ensures much more reliable mosaicing and offsetting, and is easier on observers and night assistants, but there is an extra overhead between runs of about 10 seconds compared to conventional observing.
When running under ICL the messages announcing recording transfer of data to the VAX appear on the ICL terminal.
There are some tricks to watch in the event of a system crash when running under ICL. You can abort a telescope offset run by Ctrl C on the ICL terminal. But you should clean up by typing TIDY on the same terminal twice before you try to run again. The telescope will be left where it last offset to, and you should resume the offsetting without driving back to the start position. But if you either log off from ICL (and on again) or slew the telescope, then the offset data sent to the telescope will be reset and you should then resume the next mosaic pattern with the telescope at the start position.
If you do have to restart the entire software, the procedure is:
Introduction The Telescope & Optics The Detectors
The Imaging Cameras An Imaging Cookbook The Data you Take Away
Exposure times OFFSET_RUN files CCD Windows Data Catalogs
On-line Reduction Filters Flat-fields Blank Fields Orientation Shutters
This Page maintained by : Chris Tinney (email@example.com)
This Page last updated: 29 Feb 1996, by Chris Tinney