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Spectroscopic throughput

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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.  For GMOS-N, extinction curves from Boulade et al. (1987, CFHT Bulletin 17, p.13) are used for λ < 400 nm, and from the CFHT users manual for longer wavelengths (numbers can be founds here).  For GMOS-S, CTIO spectrophotometric extinction from Stone & Baldwin (1983 MNRAS, 204, 347) and Baldwin & Stone (1984 MNRAS, 206, 241) was adopted.  The numbers available below are average values, that do not account for throughput variations as a function of grating angle.  

 

 

Site
Grating Latest throughput Plot
Previous measurements
GMOS-N
 B600 TBD TBD TBD
GMOS-N B1200 TBD TBD
TBD
GMOS-N R150 Jun/2009 Click TBD
GMOS-N R400 TBD TBD TBD
GMOS-N R600 TBD TBD TBD
GMOS-N R831 Sep/2009 Click TBD
GMOS-S B600 Oct/2009 Click TBD
GMOS-S B1200 Feb/2010 Click
TBD
GMOS-S R150
Sep/2009 Click
TBD
GMOS-S R400 Sep/2009 Click
TBD
GMOS-S R600 TBD
TBD
TBD
GMOS-S
R831 TBD
TBD TBD