Instrument's Characteristics

This page lists the main characteristic of XSHOOTER. The instrument reference guide and complete document is the XSHOOTER User Manual. The resolving power values presented below for the UVB/VIS arms still need to be refined, in particular for the 1.0" UVB and 0.9" VIS slits.

Spectrograph characteristics

Arm λ-range N. of orders

scale[1]

AB limit [2]

  (nm)   (''/pix) (mag)
UVB 300-560 12 0.16-0.20 21.2 (at 356.1 nm, ord N.21)
21.7 (at 438.8 nm, ord N.17)
VIS 550-1020 15 0.16-0.18 20.9 (at 653.8 nm, ord N.35)
20.8 (at 777.6 nm, ord N.21)
NIR [3] 1020-2480 16 0.21-0.28 21.0 (at 1245.2 nm, ord N.21)
20.6 (at 1634.4 nm, ord N.16)
18.7 (at 2179.2 nm, ord N.12)

[1] Approximate value along the slit. [2] The data collected during the UVB and VIS arm commissioning are not sufficient to provide reliable limit magnitudes. The limit magnitudes in the table are predicted by the XSHOOTER ETC which relies on the observed instrument efficiency. The accuracy of the ETC is currently limited to ~20% in the UVB and VIS arm, but is subject to continuous update and improvements. The posted values have been computed for a SNR ~ 10 in 1 hr integration time. Input parameters were: slit=1" (for the UVB, 0.9" for the VIS and the NIR), airmass= 1.2, seeing=0.8", 3 days from new moon and a power low spectrum with index =-2. [3] NIR arm values are predicted by the instrument physical model.

 

Spectrograph resolution, for the NIR arm with the new slits wheel [1]

arm slit width [2] R=(λ/Δλ) sampling arm slit width R=(λ/Δλ) sampling arm slit width R=(λ/Δλ) sampling
  (")   (pix/FWHM)   (")   (pix/FWHM)   (")   (pix/FWHM)
UVB 0.5 9900 3.2 VIS 0.4 18200 2.9 NIR 0.4 10500 2.2
  0.8 6200 5.2   0.7 10600 4.9   0.6 7780 2.9
                  0.6JH [4] 7760  
  1.0 4350 5.4   0.9 7450 7.1   0.9 5300 4.2
                  0.9JH [4] 5300  
  1.3 4000 8.1   1.2 6700 7.9   1.2 3890 5.8
  1.6 3300 9.9   1.5 5400 9.7        
UVB IFU [3] 8400 3.9 VIS IFU [3] 13200 4.0 NIR IFU [3] 8300 2.7

[1] The values in this table have been measured for all slits in each arm but the 1.3" and 1.6" for the UVB and 1.2" and 1.5" for the VIS. [2] All the slits have a fixed length of 11''. [3] The IFU FoV is 4''x1.8 '' which are re-sampled in a 0.6'' x 12 '' slit in the spectrographs. [4] The 0.6"JH and 0.9"JH are the 2 new slits with the K band blocking filter

 

Old spectrograph resolution [1]

arm slit width [2] R=(λ/Δλ) sampling arm slit width R=(λ/Δλ) sampling arm slit width R=(λ/Δλ) sampling
  ('')   (pix/FWHM)   (")   (pix/FWHM)   (")   (pix/FWHM)
UVB 0.5 9100 3.5 VIS 0.4 17400 3.0 NIR 0.4 9100 3.5
  0.8 6200 5.2   0.7 11000 4.8   0.6 6200 5.2
  1.0 5100 6.3   0.9 8800 6.0   0.9 5100 6.3
  1.3 4000 8.1   1.2 6700 7.9   1.2 4000 8.1
  1.6 3300 9.9   1.5 5400 9.7   1.5 3300 9.9
UVB IFU [3] 7900 4.1 VIS IFU [3] 12600 4.2 NIR IFU [3] 8100 2.6

[1] The values in this table have been measured for two slits in each arm and interpolated with a model for the others. [2] All the slits have a fixed length of 11''. [3] The IFU FoV is 4'' x 1.8 '' which are re-sampled in a 0.6'' x 12 '' slit in the spectrographs.

 

Detector characteristics

arm detector readout mode gain RON readout time saturation
      (e/ADU) (e) (s) (ADU)
UVB 4k x 2k E2V CCD44-82 100,1x1,hg 0.67 2.6 68
65000
    100,1x2,hg 0.67 2.6 34  
    100,2x2,hg 0.67 2.6 17
 
    400,1x1,lg 1.75 4.5 16  
    400,1x2,lg 1.75 4.5 8
 
    400,1x2,lg 1.75 4.5 4
 
VIS 4k x 2k MIT/LL CCID 20 100,1x1,hg 0.64 3.2 89
65000
    100,1x2,hg 0.64 3.2 45  
    100,2x2,hg 0.64 3.2 23  
    400,1x1,lg 1.50 5.3 21  
    400,1x2,lg 1.50 5.3 11  
    400,2x2,lg 1.50 5.3 6
 
NIR 2k x 2k Hawaii 2RG NDR 2.12 8-25[1] "1.46"
45000
AGCCD 562x528 fast 1.29 4.14 "1.2" 65535

[1] The RON depend on the DIT and is larger for short DIT. The RON~8 corresponds to a DIT larger or equal than 300s.