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Spectroscopic throughput


Spectroscopic Throughput

All throughput measurements are based on observations of spectrophotometric standards, collected under photometric conditions. Throughputs are defined as follows:

T(λ) = Nd(λ)
Nt (λ)

where: Nd(λ) is the number of photons detected with wavelength λ and Nt(λ) is the number of photons of the same wavelength hitting the telescope's primary mirror. The latter is given by:

Nt(λ) = N*(λ) 10 (-0.4 μ Aλ)

where N*(λ) is the star's photon flux at wavelength λ above Earth's atmosphere, in number of photons/cm2/s, μ is the airmass, and Aλ is a mean monochromatic extinction coefficient.

The numbers available below are average values, that do not account for throughput variations as a function of grating angle.


Instrument Gratings Latest Throughput All measurements