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Imaging Filters

NIRI contains two filter wheels and a pupil mask wheel with room for ~25 broad-band and narrow-band filters. The table below provides detailed information about the NIRI imaging filters and their availability. The Gemini identification number for each filter is recorded in the header of the data files.

Filter Name Central Wavelength
(microns)
Coverage
(microns or dl/l)
Gemini ID Transmission Curve
(click for graph)
Transmission Data* Currently In Dewar?
Broad-band filters
Y1 1.02 0.97-1.07 G0241 yes warm, cold, cold+PK50 yes
J 1.25 1.15-1.33 G0202 yes warm yes
H 1.65 1.49-1.78 G0203 yes warm yes
H-K notch - 1.45-1.76;1.93-2.29 G0236 yes warm no
K 2.20 2.03-2.36 G0204 yes warm yes
K(short) 2.15 1.99-2.30 G0205 yes warm yes
K(prime) 2.12 1.95-2.30 G0206 yes warm yes
L(prime) 3.78 3.43-4.13 G0207 yes warm yes
M(prime) 4.68 4.55-4.79 G0208 yes warm yes
Line and feature (narrow-band) filters
J-continuum1 1.065 0.8% G0239 yes warm damaged
HeI 1.083 1.5% G0234 yes warm yes
Pa(gamma) 1.094 1.5% G0240 yes warm yes
J-continuum1 1.122 0.8% G0235 no cold damaged
J-continuum1 1.207 1.5% G0232 yes warm yes
Pa(beta)1 1.282 1.5% G0221 yes warm cold yes
H-continuum1 1.570 1.5% G0214 yes warm cold yes
CH4 (short)1,5 1.58 6.5% G0228 yes warm cold yes
CH4 (long)1,5 1.69 6.5% G0229 yes warm cold yes
[FeII]1 1.644 1.5% G0215 yes warm cold yes
H2O ice 2.045 8.31% G0242 yes warm yes
HeI (2p2s)2 2.059 1.5% G0233 yes warm yes
K-continuum 2.0975 1.31% G0217 yes warm cold yes
H2 1-0 S(1)3 2.1239 1.23% G0216 yes warm cold yes
Br(gamma) 2.1686 1.36% G0218 yes warm cold yes
H2 2-1 S(1) 2.2465 1.34% G0220 yes warm cold yes
K-continuum 2.2718 1.55% G0219 yes warm cold yes
CH4 ice 2.275 6.59% G0243 yes warm yes
CO 2-0 (bh)4 2.289 1.22% G0225 yes warm cold yes
H2O ice 3.050 5% G0230 yes warm yes
hydrocarbon 3.295 1.5% G0231 yes warm yes
Br(alpha) cont 3.990 3.95-4.02 G0237 yes warm yes
Br(alpha) 4.052 4.02-4.09 G0238 yes warm no
PK-50 blocker6 N/A 0.8-2.6 G0201 yes warm yes


* Some filter scans have been done warm (covering the range from 0.8 to 3.3 microns). Cold scans taken in NIRI using the grisms are available for some filters are listed as ‘cold’ . Narrow band filter bandpasses depend on the temperature of the scan and angle with respect to the incident light. Narrow band filters were scanned at approximately a 5 degree angle.

1 Crossed with the PK-50 blocker filter to avoid long-wavelength contamination (this may not be included in the posted transmission data or graph; see each filter page for more details).

2 Crossed with the K(prime) filter to avoid long-wavelength contamination (this is not included in the posted transmission data or graph).

3 Crossed with the K filter to avoid long-wavelength contamination (this is not included in the posted transmission data or graph).

4 The CO 2-0 filter is not well-centered on the CO band; it includes considerable continuum shortward of the 2-0 band head.

5 "CH4 short" and "CH4 long" filters have considerable overlap and "CH4 long," intended to sample the continuum shortward of the methane absorption in T dwarfs, extends far into the T dwarf methane absorption band. It may be preferable to substitute the "H-continuum" filter for "CH4 short." If you contemplate using any of these filters, check the filter profiles carefully. 

6 The PK50 long-wavelength blocker goes gradually from nearly completely transmissive at the blue end of the K window to opaque at the red end. This blocker is used to block some red leaks in the other filters.