VLT-MAN-ESO-14650-4942
P96
24.06.2015
53 of 161
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
2.3.3 Overall sensitivity
The total efficiency has been measured on sky using several standard stars observed during
commissioning. Based on these values, the expected limiting AB magnitudes at blaze in 1
hour for a S/N of 10 per spectral bin are given in Figure 12. Please note that a binning 2x1 is
used while there is no possibility to bin in the NIR arm. One can also refer to the table below
with no binning.
Figure 12: Limiting AB magnitude of X-shooter per spectral bin (using 2 pixels binning in the spectral
direction) at S/N=10 in a 1 hour exposure. Other parameters: air mass 1.2, 0.8” seeing, 3 days from
new moon, 1” slit for UVB, 0.9” slit for VIS and NIR. The ESO ETC was used to compute these values.
The model uses overall efficiencies measured during commissioning. Note that these performance
estimates assume no degradation of the SNR in the extraction process or in the sky subtraction. The
decrease in efficiency to the blue side of the UVB range is due to the atmospheric absorption, at the
red side of the VIS band it is due to the decrease in efficiency of the CCD, while on the long-
wavelength side of the NIR range it is due to the rise of the thermal background.
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