The following figure shows the total efficiency of the CES when the first fibre link was installed.
The general shape is still valid, however the efficiency in the blue has been improved.
For up-to-date measurements, please check the monitoring pages.
The thin blue line depicts the inferred efficiency
accounting for the blaze function of each order;
the thick black line is an interpolation of the efficiency
measurements made at various blaze wavelengths and thus
an upper envelope to the true efficiencies.
Vertical dashed red lines mark wavelengths for which signal-to-noise
ratio calculations are presented below for stars of different spectral types and magnitudes
as a function of exposure time.
Note that the following conditions were assumed for
- Binning 1x1.
- Applying binning can improve the signal-to-noise
ratio for low count levels. To estimate this one must consider the CCD
read-out-noise of 3.4 electrons per unbinned pixel (rms)
in normal R/O mode, and take into
account the number of image pixels combined into one spectral pixel,
i.e. the width of the image slicer profile.
- Observation at blaze wavelengths where the efficiency is maximal.
- Seeing 1.0 arcsec.
- Due to the fixed aperture size of the CES fibre of
2.0 arcsec on the sky larger seeing values lead to a degradation of
- Observation at airmass 1.0 (minimum extinction).
- La Silla mean extinction values were assumed.