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. Extended source sensitivities are in mag per arcsec2. All the magnitudes are in Vega.



Broad-Band Filters

Filter Wavelength [um] Sensitivity (Vega magnitude)(*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 24.3 24.6 26.83/26.64 [26.04/25.89]
J 1.26 0.17 23.5 23.8 26.85/26.80 [26.06/26.05]
H 1.64 0.28 22.8 23.1 26.86/26.89 [26.07/26.15]
Ks 2.15 0.31 22.3 22.7 26.12/26.20 [25.33/25.45]
K 2.20 0.40 --- --- ---

(*1) The values may change in future, considering the actual measurement by deep observation.
(*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.


The Imaging ETC

The Exposure Time Calculator for broadband imaging is available. Please note that the total observation time calculated by it is just the approximate value, as it does not treat the time for dither appropriately. You can use our overhead calculator (Excel format) for a better estimate of the observing time with overhead by dither. It is available in the "Guide to Imaging Exposure Times" page.



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
NB2095(1) 2.093 0.026
H2v=1-0(3) 2.122 (ch1)
2.123 (ch2)
0.021
BrG 2.165 0.025
K-continuum(3)(5) 2.246 (ch1)
2.261 (ch2)
0.062 (ch1)
0.060 (ch2)
CO(1)(5) 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.
          (5) Turret position of CO and Kcont filters were swapped in August 2013. CO is moved to the 1st turret (for filters), while Kcont is in the 3rd turret (for grisms). Basic characteristics should not change significantly.

    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.


ND filter

A ND filter is available mainly for Ks-band dome flat acquisition (from S11A). It can also be used for JHK observation of bright standard stars with limited accuracy. For more detail, ask the SA.


Filter Attenuation Factor (temporal)
channel 1channel 2
Y 0.1811 0.1744
J 0.1778 0.1719
H 0.1853 0.1797
Ks 0.2289 0.2240

Note: values are based on the counts of dome flats with and without the ND filter (measured Feb 2014).



User Filters

We are accepting the user filters since S07A. The detail and the user filter policy can be found in the User Filter Policy page. Unfortunately, the vacant turret slot is not available for 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 2016-07-08


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