MOIRCS Filters

Broadband Filters

The following table lists the broad-band filters currently installed in MOIRCS, together with their estimated sensitivities.

Our broad band filters are designed to follow the MKO filter system (Tokunaga, Simons, and Vacca 2002, PASP, 114, 180; Warren & Hewett 2002, ASP Conf, Vol 283, 369). The transmission curves of each filter are from the data sheets from suppliers.

Estimated sensitivities listed are for a 5 sigma detection in 1 hour of integration, assuming good (0.5'') seeing and a moderately sky condition (=same sky background flux as the Subaru ETC: see also the Exposures page). Point source S/N is measured in a 1.5''-diameter aperture where we assume all the light from the source is in it. Extended source sensitivities are in mag per arcsec2. All the magnitudes are in AB unit.




Broad-Band Filters

Filter Wavelength [um] Sensitivity (AB mag)(*1) Magnitudes(*2) for
1 e-/s [1 ADU/s] for ch1/2
Name Plot List Centre Width [mag] [mag/arcsec]
Y 1.02 0.10 24.49 25.79 27.47/27.28 [26.68/26.53]
J 1.26 0.17 24.05 24.35 27.79/27.74 [27.0/26.99]
H 1.64 0.28 23.81 24.11 28.24/28.27 [27.45/27.53]
Ks 2.15 0.31 23.84 24.14 27.98/28.06 [27.19/27.31]
K 2.20 0.40 --- --- ---

(*1) For the conversion from Vega to AB magnitude we use Y_AB=Y_vega+0.64, J_AB=J_vega+0.94, H_AB=H_vega+1.38, Ks_AB=Ks_vega+1.86 (Tokunaga & Vacca 2005)
(*2) Magnitude zero points shown here is from the single observation executed on May 19, 2016.

    Notes:

    • All of our standard YJHKs filters were replaced to "fringe-free" type (wedged substrates are used) by August 2009. The Ks filter was replaced in July 2008. It is the same one used as "Ks_wedge" during S08A as a test. The J & H filters were replaced in July 2009. The transimission curves are approximately similar to the old one, but with slightly higher throughput. The transmission curves of old filters can be found here (J [img, txt], H [img, txt], Ks [img, txt]).
    • The turret position of Y-band filter was changed in July 2008.


Medium-Band Filters

Two new medium-band filters in K-band window are newly available from S23A(Note 1).


The central wavelength (CW) and band width (BW: defined by FWHM) of filters listed below are from the company-provided datasheets. The peak transmittance is almost 100 % (!) for both filters.

[Updated 2/18/23] The estimated sensitivities listed are for a 5 sigma detection in 1-hour integration, assuming a good seeing & dark sky condition(Note 2). The S/N is measured in a 1.5''-diameter aperture where we assume all the light from the source is in it. Extended source sensitivities are in mag per arcsec2. These values are in AB magnitude system.


Medium-Band Filters

Filter Wavelength [um] Typical Sky Counts [ADU/s](Note 2) Sensitivity (AB mag)(Note 3) Magnitude Zero Points
for ch1/2(Note 2)
Name Plot List Centre Width Channel 1 Channel 2 [mag] [mag/arcsec2]
K3 2.310 0.14 200 225 23.5 23.8 26.11/26.28
K4 2.410 0.12 425 480 22.8 23.1 25.82/25.99

          Notes:
          (1) They were made by the team led by Dr. Yusei Koyama (NAOJ) in 2021 with the financial aid of Subaru GLAO A-Project (ULTIMATE-Subaru Project) and opened to public use. Please read the policy for use.
          (2) These values are based on the data taken in Feb-May 2023. The actual background level largely depends on the atmospheric condition, especially for K4. We observed +-30% (for K3) to 50% (for K4) variation from day to day basis.
          (3) These values are for the channel 1. The actual 1 hr exposure data could be shallower due to some additional noise source such as the bias drift, variable sky fluctuation, the additional noise by the sky subtraction process.



Narrow-Band Filters

The central wavelength (CW) and band width (BW: defined by FWHM) of filters listed below are mostly from the direct measurement as installed in MOIRCS. The measurement values show very good agreement with the company-provided datasheets. Peak transmittance are around 80 to 90%, except for H2 and Kcont filters.

Narrow-Band Filters

Filter Wavelength [um]
Name Plot List Centre Width
NB119(2)(4) 1.1885 (ch1)
1.1886 (ch2)
0.0141 (ch1)
0.0135 (ch2)
NB1550(1) 1.548 (ch1)
1.551 (ch2)
0.018 (ch1)
0.019 (ch2)
NB1657(1) 1.657 (ch1)
1.658 (ch2)
0.020 (ch1)
0.019 (ch2)
[Fe II] 1.644 (ch1)
1.645 (ch2)
0.027
NB2071(1) 2.070 0.027
NB2083(1) 2.083 0.027
NB2095(1) 2.093 0.026
H2v=1-0(3) 2.122 (ch1)
2.123 (ch2)
0.021
BrG 2.165 0.025
CO(1) 2.298 (ch1)
2.292 (ch2)
0.023
NB2315(1) 2.317 0.026

          Notes:
          (1) They are originally the user (carry-in) filters. Please read the policy for use.
          (2) The data are not from the direct measurement but from the datasheet by supplied companies.
          (3) The transimission curve presented here is the data directly measured from the dome flat.
          (4) The background level of NB119 filter is very dark. Minimum exposure of ~30 minutes is sometimes required to reach the background-noise-limited case. Sky subtraction is generally difficult due to the change of the background.

    Sky Counts by Each NB Filter
    The measured sky counts and pattern for (some of) the NB filters can be found here and here.


    The Shift of Transmission Curve within the FOV
    The actual CWs for these filters will change as a function of the angle of incidence (AOI) to the filter. This mean that the filter transmission will have the significant dependence with the position on the image. As the filters are put on the collemated beam, the AOI will change from 0 (pointing center) to 11 deg (fartherst edge), causing the maximum shift of ~200 A for H2 filter case. Below is the example of the calculated shift for BrG filter.


  • The result of the acutal measurement for central wavelength and band width by dome flat lamp (executed in Oct 2012, Nov 2013) is available here.
  • The Microsoft Excel worksheets for wavelength shift calculation (summary as well as each filter) are also available. If you need more information, please contact to the Support Astronomer.


K-Continuum and ND Filters

The K-Continuum filter and the ND filters were decomissioned in 2022. As for Kcont filter, we instead introduced the K3 medium-band filter (MBK3). Please use the filter instead.
The ND filter (OD~0.7) was also decomissioned. If you have a request for ND filter, contact the primary SA for inquiry well before the actual use.


User Filters

We welcome the user filters. The detail and the user filter policy can be found in the User Filter Policy page. Please first contact to the primary SA if you are planning to make a carry-in filters, because the vacant slots are quite limited now.



The Old MOIRCS Filter Page

The old "MOIRCS Filter" page (for old detectors till May 2015) can be found here

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Please note that all data on these pages are subject to change as the evaluation of the performance of MOIRCS progresses.

Updated 2023-05-12


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