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Filters

A set of broad- and medium-band filters are available for imaging and spectroscopy. Some filters are installed temporarily, changing on a roughly semesterly schedule controlled by scientific demand and the limited space in the filter wheels (see the optomechanical diagrams). Please contact us in advance if you plan a proposal requiring a temporary filter.

Spectroscopy mode always requires a filter, and all filters make sense for spectroscopy. Unlike GMOS, the grisms in FLAMINGOS-2 cannot be tilted. Fixed wavelength ranges are chosen using certain filter / grism combinations, not all of which are meaningful.  For example, the medium resolution R3000 grism projects the 3rd, 4th and 5th order on the detector simultaneously, covering the K, H and J wavelength ranges, respectively. The J, H or K filters can be used to select one of the wavelength ranges.

Most commonly, the JH and HK bandpass filters are used for long-slit spectroscopy with the respective low resolution R1200 JH and HK grisms. In multi-object spectroscopy mode (to be commissioned), a narrower filter allows two spectra to be packed in dispersion direction without overlap, effectively doubling the slit density in the mask. 

Only a subsect of filters makes sense for imaging, such as the permanently installed J, H and Ks filters.

The following table lists all available filters. The throughput data include the entrance window, filter, nine lenses, and two flat mirrors, i.e. all transmissive elements. Excluded are the detector, grisms, telescope and atmosphere. The "cut-on" and "cut-off" wavelengths bracket the wavelength ranges that have at least 50% (80%) of the peak transmission.

 

Filter
name
 Currently installed
Central
λ
[µm]

Band Width

[nm]

80% cut-on
Wavelength
[µm]
80% cut-off
Wavelength
[µm]
50% cut-on
Wavelength
[µm]
50% cut-off
Wavelength
[µm]
Throughput
curves
 Imaging and spectroscopy:
Y_G0811
 NO 1.020
89.4 0.985 1.066 0.969 1.068 plot / data
J_G0802  ALWAYS 1.255
151 1.178 1.328 1.175 1.333 plot / data
H_G0803 ALWAYS 1.631
274 1.490 1.767 1.486 1.775 plot / data
Ks_G0804  ALWAYS 2.157
318 1.997 2.313 1.991 2.320 plot / data
K-blue_G0814 (a)  YES 2.060 227 1.941 2.168 1.934 2.177 data*
K-red_G0815 (a)  YES 2.310 248 2.189 2.437 2.181 2.446 data*
Spectroscopy:
JH_G0809 ALWAYS
1.390
720 1.163 1.774 0.970 1.805 plot / data
HK_G0806  ALWAYS 1.871
1067 1.308 2.401 1.261 2.511 plot / data
Jlow_G0801
 NO 1.122 132 1.056 1.189 1.048 1.192 plot / data
K-long_G0812 YES
2.200
600 1.906
2.474 1.900
2.483
data*

(a) Available on shared risk in 2017B.
(*) Filter-only transmission curve from lab measurements.