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Filters

GSAOI contains two filter wheels and one utility wheel. The two filter wheels have room for 27 broad- and narrow-band (zero redshifted) emission- and absorption line- filters. Each filter wheels also contains one blocked position for recording bias and dark frames. The list of the installed filters, central wavelengths, 50% cut-on and cut-off wavelengths, the Gemini Filter Number, transmission curves (plot and ASCII files), and the filter ID (internal) are listed in the table below.

The utility wheel contains a pupil viewer and two defocus lenses (convex and concave). The pupil viewer is used to accurately align the cold stop with GeMS exit pupil viewer and so minimize the background reaching the imager detector. The convex and concave defocus lenses produce defocused images that are used to derive static wave front phase errors at the imager detector. These phase errors are nulled using the GeMS deformable mirrors.

Transmission curves for the filters currently installed in GSAOI are shown in the figure below. The atmospheric transmission between 0.9 and 2.5 μm is superimposed as a dark green line.

Transmission curves

The table lists the properties of the filters based on lab measurements. The measurements were taken at room temperature and then calculated to 70 K using correlation measurements from a cold test witness. The measured witnesses were obtained at 298 K and 77 K and the slopes were used to determine the 70 K shift. To access the graph or the ASCII data, click on the links in the table below (plot or data). Note that the filter name is the concatenation of filter and the Gemini filter Number e.g. Z_G1101 for Z broad-band filter and CH4short_G1109 for CH4(short) narrow-band filter.

Filter Name  Central Wavelength (μm)  Coverage (μm)  50% cut-on Wavelength (μm)  50% cut-off Wavelength (μm)  Gemini Filter Number
 Transmission Curves  Filter ID
 Broad-band filters
Z 1.015
 0.170  0.930  1.100 G1101 plot / data  ED205-1
 J 1.250
 0.160  1.170  1.330 G1102 plot / data  ED191-1
 H  1.635  0.290  1.490  1.780 G1103 plot / data
 ED169-1
 K(prime)  2.120  0.340  1.950  2.290 G1104 plot / data  ED278-2
 K(short)  2.150  0.320  1.990  2.310 G1105 plot / data ED196-1
 K  2.200  0.340  2.030  2.370 G1106 plot / data  ED192-1
 Narrow-band (zero redshifted) emission- and absorption-line filters
 J-continuum 1.207
 0.018 1.198
1.216
G1107
plot / data ED190
H-continuum  1.570  0.024 1.558 1.582 G1108 plot / data  ED141
 CH4(short)  1.580  0.100 1.530 1.630 G1109 plot / data  ED144
 CH4(long)  1.690  0.100 1.640 1.740 G1110 plot / data  ED151
 K(short) continuum  2.093  0.031 2.078 2.108 G1111
plot / data  ED168
 K(long) continuum  2.270  0.034 2.253 2.287 G1112
plot / data  ED163

He I 1.083 μm

 1.083 0.016
1.075
1.091
G1115 plot / data ED185
 H I Pγ
 1.094 0.011
1.089
1.100
G1116
plot / data ED186
 H I Pβ
 1.282 0.019
1.272
1.292
G1117
plot / data ED231
 [Fe II] 1.644 μm  1.644 0.025
1.631
1.656
G1118
plot / data ED150
 H2O  2.000 0.080
1.960
2.040
G1119
plot / data ED188
 He I (2p2s)
 2.058 0.031
2.042
2.073
G1120
plot / data ED165
 H2 1-0 S(1)
 2.122 0.032
2.106
2.138
G1121
plot / data ED162
 H I Brγ
 2.166 0.032
2.150
2.182
G1122
plot / data ED166
 H2 2-1 S(1)
 2.248 0.034
2.231
2.265
G1123
plot / data ED164
 CO Δv=2
 2.360 0.080
2.320 2.400
G1124
plot / data ED187