PNS MANUAL: Taking Calibration Exposures

For each target that requires accurate wavelength calibration, it is necessary to take an image of the focal plane mask illuminated with an arc lamp. This should be done with the telescope pointing at the target, and can conveniently be done after target acquisition (the field viewing AG mirror position is the same one as that for illuminating the spectrograph with an arc lamp.)

It is best to take an arc lamp exposure after target acquisition before the first science exposure, and at the end of a sequence of exposures on the same target before moving on to the next one.

How to take calibration exposures

Arc lamps

Perform the following commands, in sequence:
  1. Issue AGCOMP command on A&G console (this puts mirror in calibration position). This can be slow; proceed meanwhile.
  2. Enter CALIB on PNS console (this puts in mask and opens shutter). Ignore the 1-second countdown.
  3. Once AGCOMP above has completed, on DAS console give arcs command. This starts 100-sec integrations on both arms. Then follow the instructions the script gives, spiced with beeps:
  4. On A&G console do COMPLAMPS CUAR+CUNE to switch on lamps.
  5. After 80 seconds you are asked to do COMPLAMPS OFF to switch them off again.
  6. A little while later the readouts will start. You may now close the shutter: SHUTC on PNS console.
  7. If the next exposure will be a science exposure, move the AG mirror back to its open position by doing AGMIRROR OUT on A&G console.

Continuum lamp

This is used to determine the filter bandpass, in conjunction with the arc lamp exposures, which indicate the wavelength scale.
  1. AGCOMP
  2. CALIB
  3. COMPND 1 - put in neutral density filter to prevent saturation
  4. ARC PNSL 100 "TUNGSTEN" &
  5. ARC PNSR 100 "TUNGSTEN" &
  6. COMPLAMPS W -- count to 12 seconds, then:
  7. COMPLAMPS OFF
  8. COMPND 0.0
  9. AGMIRROR OUT

Measured Curves

Profile of Filter B measured with the PN.S in the centre of the field at two tilt angles

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