NIRC2
Filters

The table below shows the filters are currently available with NIRC2. Note that several narrow band filters that were installed in August, 2003 are now included. The wavelength information of the new filters have been verified with NIRC2 but full characterization of the transmission curves is yet to be completed.

(Clicking on a filter name of several filters will bring up a plot of that filter's transmission curve.)

Filter
Central
wavelength
(µm)

Bandpass
width
(µm)

Cut-On Wavelength (µm)

Cut-Off Wavelength (µm)

Photometric
zeropoint
(Note: This is for Strehl = 1!!)
Sky
(mag./
sq. arcsec)
T(max)
(sec)
1.248
0.163
1.166
1.330
25.35
14.9
10,000
1.633
0.296
1.485
1.781
25.44
13.6
2750
2.196
0.336
2.028
2.364
24.63
12.6
630
2.146
0.311
1.991
2.302
24.53
12.2
630
2.124
0.351
1.948
2.299
24.74
12.2
630
3.776
0.700
3.426
4.126
23.2
2.91
0.27
4.670
0.241
4.549
4.790
21.2
-0.12
0.14
Narrow Band
Jcont
1.2132
0.0198
1.2033
1.2231
Pa Beta
1.2903
0.0193
1.2807
1.3000
Hcont
 1.5804
0.0232
1.5688
1.5920
 
 
 
CH4S
1.5923
0.1257
1.5295
1.6552
FeII
1.6455
0.0256
1.6327
1.6583
 
 
 
CH4L
1.6809
0.1368
1.6125
1.7493
He I B
2.0563
0.0326
2.0400
2.0726
Br_gamma
2.1686
0.0326
2.1523
2.1849
 
 
 
H2 v=1-0 4
2.1281
 0.0342
2.1112
2.1452
 
 
 
H2 v=2-1
2.2622
0.0388
2.2428
2.2816
      
Kcont
2.2706
0.0296
2.2558
2.2854
 
 
 
CO
2.2891
0.0267
2.2757
2.3024
BrGamma2
2.1603
0.0354
2.1426
2.1780
H2O
3.0629
0.1549
2.9855
3.1404
PAH
3.2904
0.0555
3.2627
3.3182


 

Notes:

  1. Wavelength range over which filter transmission exceeds 50% of peak.
  2. Bandpasses and central wavelengths for the narrow-band filters were measured with NIRC-2, and refer to the cold bandpasses. The broad-band filters specs refer to the room temperature measurements provided by the manufacturer.
  3. The AO bench external filter wheel normally available for NIRSPAO observing is NOT available for NIRC2. One consequence of this is that there are no ND filters in the NIRC2 optical path to help avoid saturation on bright objects. However, there are other means for avoiding saturation with NIRC2. One way is to use the very short exposure times that are possible by using the sub-array capability of the detector.
  4. The H2 v=1-0 filter was formally mislabeledesxit as "2.108" based on the manufacturer's documentation. The bandpass measurements noted in the table were made with NIRC2 and confirm that the filter correctly includes the H2 v=1-0 feature.
  5. The NIRC2 Zero point values were updated after photometric tests in April 2004.
  6. There table shows the zero-point, Z, and sky brightness, S, through various NIRC2 filters, combined with the narrow camera and the circumscribed pupil (the "open" position of the pupil wheel).
  7. Z is the magnitude of the star + 2.5 log10 (counts/sec) - 2.5 log10(Strehl). Note that the Strehl ratio will vary according to atmospheic conditions (e.g. seeing), the brightness of the AO lock star, and the distance away from the lock star.
  8. The gain, G, is 4.0 electrons/count.
  9. S is the sky brightness in magnitudes per square arcsec. The sky background in counts per pixel is given by:

    counts/sec/pixel = (arcsec/pixel)^2 * 10^[0.4*(Z-S)]

    where (arcsec/pixel) is the pixel scale, e.g. 0.040 for the wide camera.

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Last modified: 29 Sept 2003