IRIS2 Filters

 

The current filter complement is listed below. All filters are 60mm in diameter, which is required for unvignetted operation at f/8. Most of these filters were purchased as part of the Gemini IR Filter Consortium.

  • The J,H,K,Ks filters were manuactured by OCLI. These are the filters discussed in Alan Tokunaga's Papers I and II. These papers contain links to other work using NSFcam on the IRTF and IRCAM3 on UKIRT to define colour terms for these filters. The actual photometric transforms for IRIS2 are slightly different, due to those instruments using InSb (not HgCdTe) detectors, and having different optical trains. Profile measurements were made at room temperature by OCLI, however the wavelength shifts for such broad filters to the 100K operating temperatures are negligible.
  • A tar file containing the transmission curves
  • The Z filter was manufactured by NDC Infrared Engineering to Alan Tokunaga's specifications. This filter is often referred to elsewhere as "Y" to avoid confusing it with the (somewhat bluer) SDSS z' filter; however, note that the WFCAM Y filter is different again from the MKO Z/Y filter, which is closer to that defined by Hillenbrand et al. 2002.
  • The narrowband filters and methane filters were manufactured by NDC Infrared Engineering. Profiles for some of these filters have been measured in IRIS2 at IRIS2 operating temperatures - their parameters are shown in bold. Other filters for which the profiles cannot be measured directly within IRIS2 (e.g. due to being mounted in the grism wheel) have profile data taken instead from the equivalent filters within NIRI on Gemini-North.
  • The spectroscopic blocking filters were manufactured by Custom Scientific. Profile measurements for the J-band blockers were made at room temperature by Custom Scientific, however the wavelength shifts for such broad filters to the 100K operating temperatures are negligible.
  • (S) and (W) in the table below indicate typical sky counts in summer and winter, respectively. Sky counts shortward of 2 microns show less seasonal variation, but can vary by up to 30% between (and even within) nights.

 

IRIS2 Filters -  Characteristics and Performance
Filter ASCII Start
(µm)
End
(µm)
Cen
(µm)
Width
(nm)
Peak
T/put
(+/-5%)
Count Rate
(e-/s)
for 16th mag star
Approx.
Sky Counts
(e-/s/pix)
Max. Exp. (s)
(<40,000 ADU/pix)
    Profile
Source
&
Comments
Z (ASCII) 0.996 1.069 1.033 73 70 640 50 3600     Not yet
measured
J (ASCII) 1.164 1.325 1.245 161 85 2360 600 300     OCLI
H (ASCII) 1.485 1.781 1.633 296 85 2860 3200 60     "
Ks (ASCII) 1.982 2.306 2.144 324 95 1940 3900 (W)
8700 (S)
40 (W)
20 (S)
    "
K (ASCII) 2.028 2.364 2.196 336 92 1910 4700 (W)
11600 (S)
40 (W)
15 (S)
    "
He I (ASCII) 1.075 1.091 1.083 16 50   55       IRIS2
J cont (ASCII) 1.185 1.212 1.201 27 58   440       "
Red leak!
Pa beta (ASCII) 1.264 1.290 1.276 26 61   385       "
Red leak!
H cont (ASCII) 1.548 1.583 1.565 35 80   500       IRIS2
[Fe II] (ASCII) 1.623 1.653 1.633 30 80   500       "
CH4_s (ASCII) 1.531 1.652 1.590 121 90   2200       "
CH4_l (ASCII) 1.616 1.738 1.673 122 97   2200       "
H2 nu=1-0 S(1) (ASCII) 2.085 2.133 2.110 46 72   440       IRIS2
Br gamma (ASCII) 2.136 2.182 2.158 46 75   390       NIRI
H2 nu=2-1 S(1) (ASCII) 2.222 2.268 2.240 46 72   330       NIRI
K cont (ASCII) 2.246 2.283 2.255 37 80   550       NIRI
CO (2-0) bandhead (ASCII) 2.278 2.312 2.295 34 68   440       IRIS2
Spectroscopic Blockers
Jshort (ASCII) 0.954 1.256 1.096 302 80           Custom Sci
Jlong (ASCII) 1.100 1.342 1.220 242 90           "
Hspect (ASCII) 1.445 1.820 1.623 375 90           IRIS2