CES

• High-resolution image slicer.
  - If the medium- or low-resolution slicers are used, the efficiencies are increased by a factor of 1.2 or 1.25, respectively.
• 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 the efficiency.
• Observation at airmass 1.0 (minimum extinction).
• La Silla mean extinction values were assumed.

The figures show the achievable S/N ratio for exposure times between 1 and 60 min for three different spectral types and two stellar magnitudes. From top to bottom:

• B2 with V=6.0,
• B2 with V=9.0,
• A0 with V=6.0,
• A0 with V=9.0,
• G0 with V=6.0, and
• G0 with V=9.0.

As labelled in each figure the following blaze wavelengths were selected:

• 3833 Å (cyan line),
• 4267 Å (blue line),
• 5026 Å (green line),
• 6462 Å (yellow line),
• 7798 Å (red line),
• 9046 Å (magenta line), and
• 9832 Å (black line).