NIRI 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. Each filter has been (or will be) scanned and the transmission curves made available as raw data (ASCII files) and graphically. Note that some scans are 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. Narrow band filter bandpasses depend on the temperature of the scan and angle with respect to the incident light.

The blocking filters used with the grisms are different than those used for imaging. More information on these order-sorting filters can be found on the NIRI Grisms page. 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).

If graphs or data are available, click on the check-mark in the table below to retrieve them. Unless otherwise noted, filter transmission data and traces were measured warm (~300 K). Narrow band filters were scanned at approximately a 5 degree angle. Gemini's spectrophotometer only scans to 3.3 microns, so all warm transmission data end at 3.3 microns. All filters are checked for red leaks using the L and M grisms in NIRI after installation in the instrument.

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.

Almost (but not quite) all narrow-band filters have been received, and not all of those received can be installed at the same time! Check the table below for availability.

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

Last update 2007 June 15; Andrew Stephens, Tom Geballe & Joe Jensen