Notice for the S22B CfP at the Subaru Telescope

SWIMS will be open with shared risk in S22B at the Subaru Telescope as a PI-type instrument.

All applicants are required to contact the SWIMS team in advance and to include (at least) the SWIMS PI (Kentaro Motohara) as a Co-investigator.

Acceptable observing modes are normal, intensive , ToO, and service (only imaging) programs.

SWIMS Operation in S22BSWIMS is opened from S21A to S22B as a substitute for MOIRCS, and MOIRCS is in a
hibernate state. SWIMS applicants can NOT request MOIRCS as a backup instrument.
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. Note that we have only eight (8) MOS mask holders available in S22B.
IFU ModeSWIMS/IFU is a new observation mode (on a shared-risk basis) and a decision on whether
or not to open to open-use programs will be made in early April after the first engineering
night of SWIMS/IFU before TAC.
If not opened, related proposals will be declined and there will be no backups.

Notice for Service Program

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 μm. 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

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 ∼ 130 pixels.

Imag. FoV [arcmin^2]6.7 × 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 slightly broaden spectra.

Available filters/grisms

Transmission curves

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.

ASCII data for each filter transmittance :

Detector Performance

HAWAII-2RG arrays are controlled by individual readout electronics consisting of a SIDECAR ASIC and its interface board JADE-2.

Under cryogenic condition (blue ∼ 90K, red ∼ 80K), the detector performance has been assessed, as listed below.

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

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]< 0.11< 0.17< 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]∼ 16
Instrument overhead per frame [sec]∼ 11.5 + 3 * t_frame * n_read
- t_frame: frame readout time (default=1.48).
- n_read: number of Fowler sampling (default=1).
Ex) With t_frame=1.48 and n_read=1, the overhead fraction to the total observing time for 20-sec on-source exposure is (11.5 + 3 * 1.48 * 1) / (20 + 11.5 + 3 * 1.48 * 1) ∼ 0.44.

Dome flat images as of May 2021:

Multi-object Spectroscopy Unit

Instrument information

The cryogenic storage called the carousel has 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 8 slit mask frames for science use, which would constrain the number of frames available in an observing night. To use more than 9 frames requires a thermal cycle of the carousel which takes about 2 days for warming and 3 days for cooling.

Time required for operation

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 an additional 5 seconds/slot to rotate the carousel).

Missing spectral range

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 the spatial direction.

The wavelength range where the spectra falls into the gap when using the default long-slit mask is roughly 1.125--1.158 μm (blue) and 1.898--1.955 μm (red).

Integral Field spectroscopy Unit

The Integral Field spectroscopy unit for SWIMS is a "handy-size" IFU module using image-slicer optics to be installed into the MOS exchanger unit as one of the MOS masks. A notable feature is that a slice width of 0.4 arcsec is optimized for typical seeing size so that it provides the largest field of views among near-infrared IFUs for 8--10m telescopes, together with the wide wavelength coverage.

Note that the availability of the IFU mode will be decided by the Observatory in early April based on the result of the engineering observations.

Field of View [arcsec^2]13.5 × 4.8
Slice Width [arcsec]0.4
Number of Slices12 (Ch-6 -- Ch-1, Ch+1 -- Ch+6)
Expected Throughput of IFU∼ 70--75%


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

Note that the sensitivities described below may change according to the background conditions of OH airglow and thermal emission.

Data Reduction Pipeline

A reduction pipeline for imaging data is available at here. The pipeline is written in Python, which 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 anymore).

Instrument Papers


Detector Control

Multi-Object Spectroscopy Unit (MOSU)


If you have any questions, contact us at

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Last-modified: 2022-01-27 (木) 12:56:13