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The throughput of AF2/WYFFOS was measured during May
and November 2015, for the following grating / CCD combinations:
Red+4 (observation of a DA0 star). The measurements were carried out after re-coating the WYFFOS fold mirror, which has greatly enhanced
the throughput in the blue (see previous throughput measurements from May 2013 here).
The table and figure below show, as a function of wavelength, the measured
mAB zeropoints, i.e. the AB magnitude of a star giving
1 electron per second per Angstrom when observed at zenith.
The mAB zeropoints have been normalized to the median fibre throughput.
The aperture correction depends on the seeing, and on the accuracy with which the stellar image is centred on the fibre aperture. For Moffat-profile seeing, the aperture correction can be calculated from the plot on the AF2 target-acquisition page.
For the measurements, the accuracy of centring the star on the fibre was ensured to be < 0.25 arcsec by making a spirally-rastered series of observations with step 0.5 arcsec, and using the observation with the highest throughput (also coincident with the peak in the distribution of intensities, i.e. not due to a short-term seeing fluctutation). The Moffat-profile plot shows that in seeing of 0.8 arcsec, with a centring error of 0.25 arcsec, only a fraction ~0.04 of the light will be missed by the 1.6-arcsec fibre aperture.
Other errors in measured zeropoint
Zeropoints for other gratings
The relative throughput of the science fibres was measured in February 2013 with the WHTWFC detector, and is plotted in Figure 2 against fibre number. Fibres with zero throughput are disabled, i.e. cannot be configured for observing.
The measurements were obtained with the fibres configured in a circle, illuminated by sky, and are based on the mean observed intensity in the wavelength range ~4200Å to 9000 Å.
The list of relative throughputs plotted in Fig. 2 can be downloaded from here.
More information about the fibres can be found on the AF2 fibres page.
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