Under Construction.

Notice for the S21A CfP at the Subaru Telescope

SWIMS will be open with shared risk in S21A at the Subaru Telescope as a PI-type instrument.

All applicants are required to contact SWIMS team in advance.

Acceptable observing modes are normal and ToO. No intensive nor service programs are accepted.

SWIMS and MOIRCS operation in S21ASWIMS will become a near-infrared instrument at Subaru Telescope from S21A to S22B
instead of MOIRCS. Final decision on the availability of SWIMS will be made in October
2020. We note that there still remain some uncertainties related to the COVID-19 situation.
In case SWIMS is unavailable in S21A, we will consider operating MOIRCS instead (if
there is a sufficient demand as a backup instrument). Those who propose observations
with SWIMS may want to request MOIRCS instead when SWIMS becomes unavailable.
However, this option cannot change the program's scientific purpose and method. Those
who want to choose this option can write the backup plan by MOIRCS on the technical
justification section. MOIRCS will be hibernated if SWIMS will be used for the open-use
programs. In any case, Subaru Telescope will not operate MOIRCS and SWIMS simultaneously.
Necessity of MOS PreimagingSWIMS/MOS applicants who need to take pre-images with SWIMS should explicitly request
it in the "Technical Justification" of the proposal. Please check the instrument web page
for more details.
Number of MOS MasksSWIMS/MOS applicants must explicitly describe the required number of masks in Entry 16,
where the desired number as well as the minimum acceptable number should be clearly
specified. We note that there are only four (4) MOS mask holders available at the beginning
of S21A.

Brief Introduction to SWIMS

Simultaneous-color Wide-field Infrared Multi-object Spectrograph, or SWIMS, is an imager and multi-object spectrograph in the NIR wavelength of 0.9--2.5 $&u;m. The major feature is simultaneous two-color observing capability using two optical arms (blue=0.9--1.40 μm and red=1.45--2.5 μm). It provides us with

  • two-color simultaneous imaging with 6.6 × 3.3 arcmin^2 and 0.095 arcsec/pix sampling
  • R ∼ 1000 multi-object slit spectroscopy (MOS) covering 0.9--2.5 μm for ∼ 40 objects/mask at maximum.

both with a single exposure.

SWIMSComponent Assembly

Field of Views

The field of view (FoV) of the telescope is covered with two HAWAII-2RG focal plane arrays . Gaps between arrays are ∼ 2.3 mm or ∼ 130 pixels.

Imag. FoV [arcmin^2]6.6 × 3.3
Spec. FoV [arcmin^2]2.8 × 3.3
# of arrays per arm2
(4096 × 2048 pixels)
Pixel scale [arcsec/pix]0.095
FoV Layout,
Extent of spectra,
Array configuration

Light-shaded regions show the FoV for the imaging mode while dark-shaded regions for the spectroscopy mode (for full range of spectra).

Black dots represent positions of source in the imaging mode which are also equivalent to the spectral positions of undeviated wavelength (λ ∼ 1.027 μm for blue, ∼ 1.734 μm for red).

Each stripe indicates the full range of the spectrum obtained (from shorter on the left to longer wavelength on the right). Note that any optical aberrations are not considered which would make the spectrum slightly broaden.

Available filters/grisms

Blue (0.9-1.4 μm)Red (1.4-2.5 μm)
Broad-bandY (λc=1.027, Δλ=0.096) : fileplot filedata
J (1.251, 0.167) : fileplot filedata
H (1.644, 0.291) : fileplot filedata
Ks (2.139, 0.313) : fileplot filedata
Medium-bandJ1 (1.174, 0.118) : fileplot filedata
J2 (1.294, 0.123) : fileplot filedata
H1 (1.502, 0.121) : fileplot filedata
H2 (1.617, 0.116) : fileplot filedata
H3 (1.735, 0.117) : fileplot filedata
K1 (2.023, 0.138) : fileplot filedata
K2 (2.170, 0.140) : fileplot filedata
K3 (2.314, 0.128) : fileplot filedata
Narrow-bandNB1244# (1.244, 0.015) : fileplot filedata
NB1261# (1.261, 0.016) : fileplot filedata
Paβ (1.294, 0.038) : fileplot filedata
Paβ-off (1.329, 0.033) : fileplot filedata
NB1630# (1.630, 0.017) : fileplot filedata
NB1653# (1.652, 0.016) : fileplot filedata
Paα (1.876, 0.022) : fileplot filedata
Paα-off (1.948, 0.036) : fileplot filedata
NB2137# (2.133, 0.021) : fileplot filedata
NB2167# (2.164, 0.022) : fileplot filedata
GrismzJ (2.40 Å/pix, R ∼ 700-1200 w/ 0.5" slit)HKs (4.57 Å/pix, R ∼ 600-1000 w/ 0.5" slit)

Filters followed by "#" are those for SWIMS-18 survey. Requests for use for any other purpose will be also welcome.

Transmission curves

ASCII data for each filter transmittance :

Detector Performance

We utilize an ASIC, called SIDECAR, and its interface board, JADE-2, which control all of readout functions, to efficiently operate HAWAII-2RG arrays.

Under cryogenic condition (∼ 77K), the detector performance has been assessed, as listed below.

blue left (b2)blue right (b1)red left (r1)red right (r2)
Array ID and grade#17285 ENG#16321 SCI#196 SCI#206 SCI
Dark Current [e-/sec/pix]< 0.05---< 0.03< 0.06
Readout Noise (CDS and 32 Fowler) [e-]∼ 22, ∼ 7∼ 18, ∼ 4∼ 20, ∼ 4∼ 20, ∼ 5
Frame Readout Time [sec]1.48 (32-ch readout w/ 100 kHz pixel rate)
Minimum Exposure Time including Overheads [sec]∼ 8
FITS creation Timet_frame (1.48 sec) + t_exp + t_overhead (∼ 6.5 sec + t_frame*n_read)
- t_frame: time to read 2K × 2K pixels
- t_exp: exposure time for each pixel (from the 1st to the 2nd readout)
- t_overhead: parameter setting, CDS calculation, # of Fowler.
- n_read: # of Fowler sampling.

Note that Up-the-Ramp sampling mode is not available due to hardware limitation.

The cryogenic performance evaluation of Array #16321 will be completed in the next engineering run scheduled in Oct 2020. We expect to achieve the similar performance as #196 and #206.

Multi-object Spectroscopy Unit

The cryogenic storage called the carousel have 23 slots. Of them, several kinds of engineering-use masks and long-slit masks (one slot each), and one Integral Field Spectroscopy Unit (IFU) module (occupying two slots) are exclusively assigned. Other (∼ 15) slots can be used for users' MOS masks. At the moment, there are only four slit mask frames for science use, which would constrain the number of frames in a observing night. To use more than 5 frames, it requires thermal cycle of the carousel which takes about 2 days for warming and 3 days for cooling.

The time for target acquisition is about 15 minutes. The time required to exchange from one mask to another is about 2.5 minutes (and additional 5 seconds/slot to rotate the carousel).

Note that IFU function is not available in S21A.

Mask design and spectral coverage: The array gap (∼ 130 pix) produces a lack of spectral data (∼ 312 Å for blue and 594 Å for red). Pay attention to that in designing your slit mask(s). The only way to obtain the full spectral information between 0.9--2.5 μm is to prepare another slit mask in which the slit pattern is the same but all the slits are moved (more than 130 pix) along spatial direction.


Total throughput including the telescope and the atmosphere is evaluated to be ∼ 0.4 for imaging and ∼ 0.3 for spectroscopy.

The following sensitivities (AB mag) are calculated with assumptions of seeing size=0.5 arcsec (photometry aperture radius=0.5 arcsec for point source or spatial extent=5.0 arcsec for extended source), exposure time=1 hr, and S/N=5.

Note that these values may change according to the background conditions of OH airglow and thermal emission.

  • Imaging
    Point source [mag]Y=25.2, J=24.9, H=24.2, Ks=24.4J1-2~25.0, H1-3~23.7, K1-3~24.0
    Extended source [mag/arcsec^2]TBWTBW
  • Spectroscopy (slit width=0.5" assumed, no binning applied along wavelength direction)
    Point source [mag]J=21.1, H=20.7, Ks=20.9
    Extended source [mag/arcsec^2]TBW

Data Reduction Pipeline

We offer a reduction pipeline for imaging data. The pipeline is written in Python, which has been confirmed to work with Python 2.7 and 3.7, and follows standard procedures from flat-fielding to final stacking.

We have no dedicated tools for spectroscopic data at the moment. Other pipelines such as MCSMDP for MOIRCS may work with SWIMS data, or certainly IRAF is also useful (although it has not been maintained any more).

Instrument Papers


Detector Control

Multi-Object Spectroscopy Unit (MOSU)


If you have any questions, contact us at

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Last-modified: 2020-08-03 (月) 18:16:53