Simple exposures

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Simple exposures

Initially we assume that your images will be two dimensional. That is, we assume that you requested only one image plane per observation when you set up the system.

Most observations are started with one of the commands run, arc, flat, dark, bias, flash sky or map. Each of these commands

produces a single data-set from a single channel;
saves the data to disk for later export on FITS tape;
records the observation in the observing log.

The command names correspond to the intended use of the image and are recorded in the FITS header under the keyword OBSTYPE. Run implies a science frame, flat implies a dome or lamp flat-field, sky a sky-flat or fringe-frame, map an exposure to map the geometry of an instrument. Dark and bias do not open the detector's shutter. Bias and flash take bias frames, without preflash and with preflash respectively.

It is important to remember that none of these commands affect the instrument; using the arc command, for example, won't turn on arc lamps or set up the A&G box for calibration exposures. All exposure commands except bias preflash the CCD if a non-zero time has been set for the preflash. For example

ICL> run red 100 "NGC 1068"

requests a run of length 100 seconds on the Red channel ( i.e. on the red arm of Isis) and gives a title for the observation. The title appears in the observing log and is written to the FITS keyword OBJECT. The system will allocate a run number to the run and will tell you the number. The data are saved in the directory pointed to by the logical name RUN_FILES. Use the command

ICL> dir

whenever you want to check the contents of this directory. A naming convention exists: run 4151 would be written to a file named R4151.SDF. All the runs from a given night's observing appear in the same directory.

To take data simultaneously on the red and blue arms of Isis, just type

ICL>  run red  <exposure time> "

and the exposure will proceed in parallel. This also applies to any other set of channels that can receive light simultaneously. Previous: Making exposures Up: Making exposures Previous Page: Making exposures Next Page: Multiple sequential exposures Mon Oct 3 21:59:29 WET 1994