1. Programs & Projects
  2. Mid-Scale Observatories — Cerro Tololo Inter-American Observatory
  3. Current Instruments
  4. COSMOS
  5. COSMOS Dispersers
  6. COSMOS Dispersers

COSMOS Dispersers

Six dispersers are avilable for use with COSMOS. The properties of dispersers are listed in the table below.

Disperser1

Fringe Frequency

(lines/mm)

Blaze 

Resolution with

3 pixel (0.9") slit

Wavelength Range2

(Å)

Dispersion3

(Å/pixel)

Blocking Filter
Blue (b2k) 1172 500nm 24004 3480 - 6190 0.66 NA
3795 - 6615 0.69 NA
4150 - 7050 0.71 GG-395
Red (r2k) 842 800nm 23005 4985 - 9040 0.99 GG-455
5515 - 9635 1.00 OG-530
6080 - 10250 1.02 OG-570
High-Res Blue (hb4k) 1886 480nm 40004 3770 - 5450 0.41 NA
4000 - 5695 0.41 NA
4230 - 5950 0.42 NA
Visible (v4k) 1508 600nm 39006 4805-6860 0.50 GG-395
5070-7170 0.51 GG-395
5350-7485 0.52 GG-395
Wide (l2k)7 905 480nm 18004 2845-6250 0.83 NA
3160-6825 0.90 NA
3570-7420 0.94 NA/GG-3958

High-Res Red (hr4k)

(OUT OF SERVICE)

 1141 790nm 38009 6065-8925 0.70 GG-495
6445-9340 0.71 GG-495
6845-9765 0.71 GG-495

1 COSMOS can hold up to five dispersers at a time. The number of dispersers that can be used during a night is limited by the time available for afternoon calibrations.
2The wavelength ranges given for each disperser correspond to the blue, center, and red slits respectively.
3 The dispersion given for each disperser corresponds to the blue, center, and red slits respectively. The dispersions were found by using the IRAF tasks "identify" and "reidentify" along the dispersion and spatial axes. The resulting surface was fit as a polynomial using "fitcoords" and then linearized using "transform" in the "twodspec" package.
4 At 5000Å….
5 At 7000Å….
6 At 6000Å….
7 The COSMOS optics are transmissive down to 3600Å…. There is little value in using this grism with either the blue or center slits.
8 This grism and slit combination can be affected by 2nd-order blue light from 3600Å… - 3700Å… appearing between 7200Å… - 7400Å… if the GG-395 blocking filter is not used. If this filter is used, light below 3950Å… will not be transmitted.
9 At 8000Å….

Updated on May 6, 2021, 5:22 pm