PNS MANUAL: Taking Flux standards

How to take exposures of flux standards

The PNS shutter is rather slow. For calibration of the photometry with bright flux standards the shutter would introduce large uncertainties. The procedure described below involves leaving the shutter open, and letting the CCD integration time determine the exposure time. As the CCDs are windowed, the beginning of the readout is a fast parallel transfer of the charges, ensuring accurate photometry on the flux standard.

Note that an offest of ~30" should be taken in the dispersion direction (N-S if PA=0, E-W if PA=90) for all flux standards in order to avoid the bad column in the centre of EEV13.

Perform the following commands, in sequence:

  1. Once target acquisition is complete, make sure A&G mirror is OUT (check A&G mimic display). If it is not, issue AGMIRROR OUT on A&G console.
  2. On PNS console issue SHUTO command (opens shutter).
  3. On PNS console issue MASKO command if there is doubt the mask may be in.
  4. On DAS console issue fluxstd time "title" (performs a readout of time seconds). 20 seconds on an 11th mag star works well.
  5. When finished, issue SHUTC command on PNS console to close shutter.

For list of Galactic PNe, see here.

For a list of suitable La Palma Flux standards, download pnsflxstd.cat.

These have been selected to have smooth spectra near 500nm, to be bright (10-12m), and to be South of Zenith from La Palma (to prevent long slews). The file can be loaded into the WHT catalogue list.
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