Coudé Gratings
The gratings available with the coude spectrograph include the four
conventional coude gratings (A, B, C, and D), the echelle grating, and
the full set of gratings from the 4m RC Spectrograph. The echelle
grating can be used with grisms from the 4m Cryogenic Camera to provide
cross dispersion, and the echelle grating gives resolutions of
approximately 100,000 on Camera 5 and 250,000 on Camera 6. The RC
gratings are used for lower resolution work with wide spectral
coverage.
Designation A B C D
Ruled Area (mm) 304x361 309x370 204x254 204x308
Grooves/mm 632 316 600 1200
Blaze (A), 1st Order 12000 12000 8000 8000
Blaze Angle... 22.3 11. 13.9 28.8
ghost intensity (%) 0.005 0.002 0.06 0.1
Grooves Blaze (A) Dispersion (A/mm)
Grating per mm 1st Order Cam. 5 Cam. 6
RC-250 158 4000 60 17
RC-400 158 8000 60 17
KPC-10A 316 4000 30 8.4
RC-181 316 7500 30 8.4
KPC-7 632 5200 15 4.2
RC-450 632 11000 15 4.2
KPC-17 527 5540 18 5.3
KPC-18 790 8500 12 3.3
Only
cameras 5 and 6 are available with
CCD detectors. Cameras 2 and 3
are available with photographic plates only, and are generally not
used.
Camera 5 Camera 6
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Grating blue red I blue red
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reciprocal A 4.7 7.0 1.4 2.1
dispersion B 9.9 14.8 2.8 4.2
(A/mm) C 7.8 15.7 2.2 4.4
D 3.8 7.6 1.1 2.2
ECH 1.2 1.8 0.32 0.51
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resolution(A) A 0.14 0.21 0.04 0.06
(for 2 pixel B 0.30 0.44 0.08 0.12
line width, C 0.23 0.47 0.06 0.13
TI CCD,0.015 D 0.12 0.23 0.04 0.06
mm pixels $) ECH 0.035 0.055 0.0096 0.015
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spectral A 56 84 16 25
coverage (A) B 118 177 34 50
TI CCD C 94 188 26 52
(800 pixels #) D 45 91 12 26
ECH 14.0 22.0 3.84 6.0
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exposure time A 450 300 *1500 *1000
(sec) for B 200 150 *600 *300
S/N=100 C 300 400 *900 *400
(feed tel) D 500 300 *2000 *1000
(V=6.0) ECH 1800 900
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*Using on-chip pixel summation perpendicular to dispersion.
$Multiply by: 1.4 - S2KA; 1.6 - T1KA,T2KA(B); 1.8 - TEK2
#Multiply by: 3.58 - S2KA; 2.05 - T1KA, 4.10 - T2KA(B);
1.15 - TEK2, 3.87 - FO3K