CES @3.60m :: Total efficiency

La Silla - Science Operation Department

CES efficiency and signal-to-noise ratios

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Total efficiency and signal-to-noise

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.

[Total efficiency (end-to-end throughput) of the CES]

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.

[Achievable signal-to-noise ratios for a B2 star of V=6.0 mag]

[Achievable signal-to-noise ratios for a B2 star of V=9.0 mag]

[Achievable signal-to-noise ratios for an A0 star of V=6.0 mag]

[Achievable signal-to-noise ratios for an A0 star of V=9.0 mag]

[Achievable signal-to-noise ratios for a G0 star of V=6.0 mag]

[Achievable signal-to-noise ratios for a G0 star of V=9.0 mag]

Note that the following conditions were assumed for these plots:

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.