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Imaging Filters

NIRI contains two filter wheels and a pupil mask wheel with room for about 25 broad and narrow-band filters. The list presented in this table is subject to change as new filters arrive, but generally only those filters listed as arrived at the time of the call for proposals for a given semester will be considered for use during that semester. Near the beginning of a semester the filters required for that semester's programs will be installed. Where more filters are required than available choices will be made based on ranking of programs and demand.

Each filter has been (or will be) scanned and the transmission curves made available as raw data (ASCII files) and graphically. Some 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 as well. If graphs or data are available, click on the link in the table below to retrieve them. 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.

NIRI also has a PK50 long-wavelength blocker that 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. For narrow band filters in the K window, the broad-band K filter is used instead (if necessary). All filters have been checked for red leaks using the L and M grisms in NIRI after installation in the instrument and where needed blocking filters (e.g., PK50) have been installed.

The blocking filters used with the grisms are different than those used for imaging. Information on these order-sorting filters can be found in the Spectroscopy section of these pages.

Unique identification numbers for each filter are listed in the table.These ID numbers are also written to the headers of the data images to allow unambiguous identification of the filter used for a particular observation.

Here are additional notes on a few of the filters. The CO 2-0 filter is not well-centered on the CO band; it includes considerable continuum shortward of the 2-0 band head. Also, the "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.

Filter Name Central Wavelength
(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 no
HeI 1.083 1.5% G0234 yes warm yes
Pa(gamma) 1.094 1.5% G0240 yes warm no
J-continuum1 1.122 0.8% G0235 no cold yes
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 1.58 6.5% G0228 yes warm cold yes
CH4 (long)1 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 no
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 no
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) 2.289 1.22% G0225 yes warm cold no
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 blocker N/A 0.8-2.6 G0201 yes warm yes

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).