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ALFOSC grism data

Grism rules/mm blazea central dispersion resolution for
0.5 arcsec slit
resolution for
1.0 arcsec slit
[Â] [Â] [Â/pixel] R=/ [Â] R=/ [Â] [Â]
3 400 39004320 2.3 6906.2 35012.4 3200-6700
4 300 48005800 3.0 7108.1 36016.2 3200-9100
5 i 300 65007000 3.1 8308.4 41516.8 5000-10250
6 600 39004020 1.5 9804.1 490 8.2 3200-5550
7 600 53005260 1.5 13004.1 650 8.2 3850-6850
8 i 600 65007030 1.3 20003.5 1000 7.0 5825-8350
9 c 79 17 orders0.4 @ 5000Â
0.7 @ 7500Â
4500
3900
1.1
1.9
2250
1950
2.2
3.8
3300-11000
10 e 150 38003870 6.5 21018 10536 3300-10550
11 e 200 52005000 4.8 38013 19026 3900-9950
12 e i 75 73006930 13 19036 9572 5100-11000
13 c f 316 51005250 0.5 37001.4 18502.8 4800-5800 g
13 c 316 4 orders 0.35 @ 4050Â
0.5 @ 5250Â
4300
3700
1.0
1.4
2150
1850
2.0
2.8
3350-8660 h
14 600 42884630 1.4 12003.8 6007.6 3275-6125
15 f 300 52685470 3.1 6508.4 32516.8 3200-9125
16 1000 40694280 0.77 2000 1.9 1000 3.8 3500-5060
17 2400 VPH
6580 0.26 100000.65 5000 1.3 6350-6850
18 1086 VPH
4360 0.82 20002.2 1000 4.4 3520-5190
19 823 VPH
5640 1.10 19402.9 970 5.8 4510-6670
20 484 VPH
7850 1.95 15405.1 770 10.3 5850-9840

Grism [Â] 2nd order j Peak-to-peak fringe levels k
3 3200-6700 U 20% noticeable >6100 no fringes in wav range
4 3200-9100 U 20% noticeable >5900; B 5% start 6700Â, 7% at 7500Â, 20-25% >8000Â
5 5000-10250 B/V 20% noticeable >9700 start 6700Â, 8% at 7500Â, 18% at 8000Â, >30% >9000Â
6 3200-5550 no 2nd-order light in wav range no fringes in wav range
7 3850-6850 U >10% noticeable >6200 no fringes in wav range
8 5825-8350 no 2nd-order light in wav range start 6500Â, 10% at 7500Â, >25% >8000Â
10e3300-10550U 2.5% noticeable >6200; B 0.5% start 7500Â, 6% at 8000Â, 13% at 9000Â, >25% >9500Â
11e3900-9950 14% at 4000Â noticeable >6900; B 4% start 6800Â, 5% at 7500Â, 17% at 8500Â, 20-35% 9000-10000Â
12e5100-11000V 20% noticeable >9900; R 9% start 7500Â, 3-5% 8000-10000Â
14 3275-6125 no 2nd-order light in wav range no fringes in wav range
15f 3200-9125 U 25% noticeable >6100; B 5% start 6500Â, 9% at 7500Â, 19% at 8000Â, >25% >8500Â
16 3500-5060 no 2nd-order light in wav range no fringes in wav range
17 6350-6850 no 2nd-order light in wav range start 6400Â, 5% at 6600 Â, 10% at 6800 Â
18 3520-5190 no 2nd-order light in wav range no fringes in wav range
19 4510-6670 no 2nd-order light in wav range TBD
20 5850-9840 no 2nd-order light in wav range TBD

Click on the waveband to obtain an efficiency/transmission curve.
Click here for count rates.

Notes to the tables

a) Effective blaze wavelength, where measurements are available.
b) With a 0.5" slit.
c) Echelle grism.
e) Grisms 10, 11 and 12 are cross-dispersers for grism 9. They can also be used as individual low-res grisms.
f) These grisms project the spectrum from red to blue on the chip.
g) This range is obtained with a special order sorter filter which is mounted in a square ALFOSC filterholder and located in its own drawer. The filter has NOT filter ID #124 (see the filter list).
h) This wavelength range has gaps and is obtained with grism #10 as cross-disperser (see below).
j) This column lists the UBVR peak flux of the 2nd order wrt that of the 1st. These were measured with U#7, B#74, V#75, and R#76.
k) The peak-to-peak fringe levels were measured with CCD#7 (Loral), except for grism#17 (CCD#8). See a comparison between CCD#7 and CCD#8.
i) Grisms #5, #8 and #12 have an in-built blocking filter OG515. For grisms #5 and 12# there is a remaining 2nd-order effect, see Table above.


Echelle mode

Grisms #9 and #13 are Echelle grisms, that image multiple orders on the CCD. They have to be used together with a cross-disperser (Gr #10, #11, #12) or with an order sorting filter. Below the possible setups are described. Note that special Echelle slitlets need to be used when a cross disperser is used.

  • Grism 9+10: spacial order overlap bluer than 4250Â, for the standard 8 arcsec slit length. The total wavelength range sampled is 3300-10350Â; the wavelength range with proper inter-order spacing is 4250-10350Â.
    Cross-disp is flipped with respect to g9+11 and g9+12.

  • Grism 9+11: noticable 2nd order effects (2nd order of g11) redward from 7400Â.The total wavelength range sampled is 3900-10350Â.

  • Grism 9+12: Good throughput in the red, but not very useful. Cross-dispersion too low except for echelle orders 6,7,8 corresponding to 7500-11000Â. Redward from 10000Â there are very significant 2nd order effects (from g12). Note that the Loral chip fringes 40% peak-to-peak in echelle order 7 (around 9500Â).

  • Grism 13+10: Grism 13 is usualy used with an order sorting filter in 3rd order, but can also be used with a cross-disperser. Grism 13+10 give an alternative for Grism 9+10, as spacial overlap is not a problem for this combination. For medium-resolution spectroscopy bluer than 4250Â this option is preferred over Grism 9+10. The orders of Grism 13 are too long for the chip: the total wavelength coverage is 3350-3610 (5th order), 3720-4430, 4770-5830, 7020-8660 (2nd order).



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