Integral field spectroscopy (IFS) is an observational method for obtaining spatially resolved spectra over a specific field of view (FoV) in a single exposure. In recent years, near-infrared IFS has gained importance in observing objects with strong dust attenuation or at a high redshift. One limitation of existing near-infrared IFS instruments is their relatively small FoV, less than 100 arcsec2, compared with optical instruments. Therefore, we developed a near-infrared (0.9 to 2.5 μm) image-slicer type integral field unit (IFU) with a larger FoV of 13.5×10.4 arcsec2 by matching a slice width to a typical seeing size of 0.4 arcsec. The IFU has a compact optical design utilizing off-axis ellipsoidal mirrors to reduce aberrations. Complex optical elements were fabricated using an ultra-precision cutting machine to achieve root mean square surface roughness of less than 10 nm and a P-V shape error of less than 300 nm. The ultra-precision machining can also simplify the alignment procedures. The on-sky performance evaluation confirmed that the image quality and the throughput of the IFU were as designed. In conclusion, we successfully developed a compact IFU utilizing an ultra-precision cutting technique, almost fulfilling the requirements.
The Simultaneous-color Wide-field Infrared Multi-object Spectrograph (SWIMS) is one of the 1st generation facility instruments for the University of Tokyo Atacama Observatory (TAO) 6.5 m telescope currently being constructed at the summit of Cerro Chajnantor (5,640 m altitude) in northern Chile. SWIMS has two optical arms, the blue arm covering 0.9–1.4 µm and the red 1.4–2.5 µm, by inserting a dichroic mirror into the collimated beam, and thus is capable of taking images in two filter-bands simultaneously in imaging mode, or whole nearinfrared (0.9–2.5 µm) low-to-medium resolution multi-object spectra in spectroscopy (MOS) mode, both with a single exposure. SWIMS was carried into Subaru Telescope in 2017 for performance evaluation prior to completion of the construction of the 6.5 m telescope, and successfully saw the imaging first light in May 2018 and MOS first light in Jan 2019. After three engineering runs including the first light observations, SWIMS has been accepted as a new PI instrument for Subaru Telescope from the semester S21A until S22B. In this paper, we report on details of on-sky performance of the instrument evaluated during the engineering observations for a total of 7.5 nights.
SWIMS-IFU is an image-slicer integral field unit designed for Simultaneous-color Wide-field Infrared Multi-object Spectrograph (SWIMS) of the University of Tokyo Atacama observatory 6.5m telescope. Its field-of-view, slice width and slice number are 17.2 ′′ × 12.8 ′′, 0.4 ′′ and 26, respectively. Due to the space limitation inside SWIMS, the IFU should fit in the dimension of 60mm×170mm×220mm. After finishing development of optical design, we have conducted tolerance analysis. The results show that the probability of vignetting of less than 5% is ∼90%, although at a slice of one side it drops to 50%. We plan to fabricate the mirror arrays monolithically by a ball-end milling with an ultra-high precision machine tool, and have conducted a demonstration process to prove its feasibility. Our requirement for shape error is less than 100 nm P-V and that for surface roughness is less than 10 nm r.m.s. Results of the latest demonstration satisfies the requirement. We will fabricate the mirror arrays and the support structures in 2018, and the IFU will be installed into SWIMS in 2019.
The Simultaneous-color Wide-field Infrared Multi-object Spectrograph, SWIMS, is a first-generation near-infrared instrument for the University of Tokyo Atacama Observatory (TAO) 6.5m Telescope now being constructed in northern Chile. To utilize the advantage of the site that almost continuous atmospheric window appears from
0.9 to 2.5 μm, the instrument is capable of simultaneous two-color imaging with a field-of-view of 9.′6 in diameter or λ/▵λ 1000 multi-object spectroscopy at 0.9–2.5 μm in a single exposure. The instrument has been trans- ported in 2017 to the Subaru Telescope as a PI-type instrument for carrying out commissioning observations before starting science operation on the 6.5m telescope. In this paper, we report the latest updates on the instrument and present preliminary results from the on-sky performance verification observations.
Simultaneous-color Wide-field Infrared Multi-object Spectrograph, SWIMS, is one of the first generation instruments for University of Tokyo Atacama Observatory 6.5m Telescope where almost continuous atmospheric window from 0.9 to 2.5μm appears, thanks to the high altitude and dry climate of the site. To utilize this excellent condition, SWIMS is capable of simultaneous two-color imaging with a field of view of 9’. in diameter and λ/Δλ ~1000 multi-object spectroscopy at 0.9–2.5μm in a single exposure, utilizing a dichroic mirror inserted in the collimated beam. Here, we overview the instrument, report results of its full-assembly tests in the laboratory and present the future plan.
MIMIZUKU is the first-generation mid-infrared instrument for the university of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU provides imaging and spectroscopic monitoring capabilities in a wide wavelength range from 2 to 38 μm, including unique bands like 2.7-μm and 30-μm band. Recently, we decided to add spectroscopic functions, KL-band mode (λ= 2.1-4.0 μm; R =λ/Δλ ~ 210) and 2.7-μm band mode ( λ= 2.4-2.95 μm; R ~ 620), and continuous spectroscopic coverage from 2.1 to 26 μm is realized by this update. Their optical designing is completed, and fabrications of optical elements are ongoing. As recent progress, we also report the completion of the cryogenic system and optics. The cryogenic system has been updated by changing materials and structures of thermal links, and the temperatures of the optical bench and detector mounting stages finally achieved required temperatures. Their stability against instrument attitude is also confirmed through an inclination test. As for the optics, its gold-plated mirrors have been recovered from galvanic corrosion by refabrication and reconstruction. Enough image quality and stability are confirmed by room-temperature tests. MIMIZUKU is intended to be completed in this autumn, and commissioning at the Subaru telescope and scientific operations on the TAO telescope are planned in 2017 and around 2019, respectively. In this paper, these development activities and future prospects of MIMIZUKU are reported.
SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph) is a near-infrared imager and multi-object spectrograph as one of the first generation instruments for the University of Tokyo Atacama Observatory (TAO) 6.5m telescope. In this paper, we describe an array control system of SWIMS and results of detector noise performance evaluation. SWIMS incorporates four (and eight in future) HAWAII-2RG focal plane arrays for detectors, each driven by readout electronics components: a SIDECAR ASIC and a JADE2 Card. The readout components are controlled by a HAWAII-2RG Testing Software running on a virtual Windows machine on a Linux PC called array control PC. All of those array control PCs are then supervised by a SWIMS control PC. We have developed an "array control software system", which runs on the array control PC to control the HAWAII-2RG Testing Software, and consists of a socket client and a dedicated server called device manager. The client runs on the SWIMS control PC, and the device manager runs on the array control PC. An exposure command, issued by the client on the SWIMS control PC, is sent to the multiple device managers on the array control PCs, and then multiple HAWAII-2RGs are driven simultaneously. Using this system, we evaluate readout noise performances of the detectors, both in a test dewar and in a SWIMS main dewar. In the test dewar, we confirm the readout noise to be 4.3 e- r.m.s. by 32 times multiple sampling when we operate only a single HAWAII-2RG, whereas in the case of simultaneous driving of two HAWAII-2RGs, we still obtain sufficiently low readout noise of 10 e- r.m.s. In the SWIMS main dewar, although there are some differences between the detectors, the readout noise is measured to be 4:1−4:6 e- r.m.s. with simultaneous driving by 64 times multiple sampling, which meets the requirement for background-limited observations in J band of 14 e- r.m.s..
We describe overview of fabrication methods and measurement results of test fabrications of optical surfaces for an integral field unit (IFU) for Simultaneous color Wide-field Infrared Multi-object Spectrograph, SWIMS, which is a first-generation instrument for the University of Tokyo Atacama Observatory 6.5-m telescope. SWIMS-IFU provides entire near-infrared spectrum from 0.9 to 2.5 μm simultaneously covering wider field of view of 17" × 13" compared with current near-infrared IFUs. We investigate an ultra-precision cutting technique to monolithically fabricate optical surfaces of IFU optics such as an image slicer. Using 4- or 5-axis ultra precision machine we compare the milling process and shaper cutting process to find the best way of fabrication of image slicers. The measurement results show that the surface roughness almost satisfies our requirement in both of two methods. Moreover, we also obtain ideal surface form in the shaper cutting process. This method will be adopted to other mirror arrays (i.e. pupil mirror and slit mirror, and such monolithic fabrications will also help us to considerably reduce alignment procedure of each optical elements.
We propose and demonstrate an optical component that overcomes critical limitations in our previously demonstrated high-speed multispectral videography—a method in which an array of periscopes placed in a prism-based spectral shaper is used to achieve snapshot multispectral imaging with the frame rate only limited by that of an image-recording sensor. The demonstrated optical component consists of a slicing mirror incorporated into a 4f-relaying lens system that we refer to as a spectrum slicer (SS). With its simple design, we can easily increase the number of spectral channels without adding fabrication complexity while preserving the capability of high-speed multispectral videography. We present a theoretical framework for the SS and its experimental utility to spectral imaging by showing real-time monitoring of a dynamic colorful event through five different visible windows.
SWIMS-IFU is an integral field unit for a near-infrared imaging spectrograph SWIMS (Simultaneous-color
Wide-field Infrared Multi-object Spectrograph), which is being developed as one of the first-generation instruments for the University of Tokyo Atacama Observatory (TAO) 6.5-m infrared telescope and will be also mounted
on the Cassegrain focus of the Subaru telescope in its initial phase (2015-). As SWIMS has a wide wavelength
coverage which is implemented by a dichroic mirror placed into the collimated beam which splitting it into blue
(0.9-1.4 μm) and red (1.4-2.5 μm) arms, the IFU module enables us to simultaneously obtain spatially resolved
entire NIR spectrum from 0.9 to 2.5 μm in a wide-field of view of 14 ′′ x 10.′′4. The concept of the IFU module is
"easy realization" of an integral filed spectroscopy (IFS) mode without modification of an existing spectrograph
optics. Our IFU can be installed in a mask storage of SWIMS like other slit mask holders, so we can easily
carry out IFS observation by just inserting the IFU module into a focal plane stage. The IFU optics consists of
a pre-optics, an image slicer, a pupil mirror array, and a pseudo-slit mirror array. All the components will be
aligned on an aluminum frame which has a floor size of < 170mm x 220mm) and a height of <60mm. Compared
to existing near-infrared IFU instruments, our IFU has wider field coverage and is more sensitive for extended
sources due to its coarser spatial sampling optimized for seeing-limited observations. In this paper, we report
the concept and detailed optical design of the SWIMS-IFU.
SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph) has a multi-object spectroscopic function including IFU in addition to the imaging capability. The mechanism in order to achieve this function is Multi-Object Spectroscopy Unit. This is the function that can derive spectra of simultaneous 20–30 objects over range from 0.9 to 2.5μmm. To set or exchange a slit mask on telescope focal plane, MOSU consists of the slit-mask dewar (carrousel), focal plane dewar, and robotic arm called mask catcher. There are many structural and mechanical features in MOSU to achieve its performance in cooling system, positional repeatability of slit mask and so on. We present here its unique components and its specifications and performance.
Simultaneous Color Wide-field Infrared Multi-object Spectrograph, SWIMS, is one of the first generation in- struments for the University of Tokyo Atacama Observatory (TAO) 6.5m Telescope now under construction. A dichroic mirror being inserted in the collimated beam, it is capable of two-color simultaneous imaging with FoV
of 9:16φ or R ∼ 1000 multi-object spectroscopy at 0.9–2.5μm wavelength range in one shot, and enables us to
carry out efficient NIR imaging/spectroscopic survey of objects such as distant galaxies and young stellar objects.
All the major components have been fabricated and we will start integration and laboratory cool-down test in the summer of 2014. After the engineering and initial science observations at the Subaru telescope, SWIMS will be transported to TAO telescope and see the first light in 2018.
SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph) is one of the first-generation instru- ments for the University of Tokyo Atacama Observatory 6.5-m telescope which is now under construction in northern Chile. This instrument incorporates 4 (and maximum 8 in future) HgCdTe HAWAII-2RG detectors, from which images are acquired by SIDECAR ASICs. Characterization and validation of performances of these detectors are carried out using a test dewar at 80K using liquid nitrogen. Bias voltages such as reset level and substrate level and reference voltages are optimized to minimize readout noise with keeping output levels within proper range for ADC inputs. ADU-electron conversion gain gc is measured by photon-transfer method, incorporating IPC (Inter-Pixel Capacitance) correction. IPC coefficient is measured to be about 1.4%, which result in overestimation of gc by about 13%. After this correction, gc is measured to be about 2:4 e-=ADU with normal preamplifier gain setting in the ASICs. Correlated double sampling (CDS) readout noise is about 16 e- rms, and is reduced to about 4 e- rms by Multi Fowler sampling. The noise is different by 30% at most between channels of the ASIC. We also separate noise sources into those come from detector pixels, from a at cable between the detector and the ASIC, and from preamps and from ADCs, and found that the detector pixels are the major sources of readout noise. Fitting of linearity curve is also obtained. The next step is to study the effects of driving multiple detectors to the performances and to install the detectors into SWIMS.
The MIMIZUKU is the first-generation mid-infrared instrument for the TAO 6.5-m telescope. It challenges to prove the origin of dust and the formation of planets with its unique capabilities, wide wavelength coverage and precise calibration capability. The wide wavelength coverage (2-38 μm) is achieved by three switchable cameras, NIR, MIR-S, and MIR-L. The specifications of the cameras are revised. A 5μm-cutoff HAWAII-1RG is decided to be installed in the NIR camera. The optical design of the MIR-L camera is modified to avoid detector saturation.
Its final F-number is extended from 5.2 to 10.5. With these modifications, the field of view of the NIR and MIR-L camera becomes 1.2’ × 1.2’ and 31” × 31”, respectively. The sensitivity of each camera is estimated based on the
revised specifications. The precise calibration is achieved by the “Field Stacker” mechanism, which enables the simultaneous observation of the target and the calibration object in different fields. The up-and-down motion
of the cryostat (~ 1 t), critical for the Field Stacker, is confirmed to have enough speed (4 mm/s) and position accuracy (~ 50 μm). A control panel for the Field Stacker is completed, and its controllers are successfully
installed. The current specifications and the development status are reported.
ANIR (Atacama Near InfraRed camera) is a near infrared camera for the University of Tokyo Atacama 1.0m telescope installed at the summit of Co. Chajnantor (5640m altitude) in northern Chile. The high altitude and the extremely low water vapor (precipitable water vapor:PWV=0.5mm) of the site enables us to perform observation of hydrogen Paschen alpha (Paα) emission line at 1.8751 μm. Since the first light observation in June 2009, we have succesfully obtained Paα narrow-band images of Galactic objects and near-by Galaxies. However, as there are many atmospheric absorption features within the wavelength range of the narrow-band filters which vary temporally due to change of PWV, it is difficult to calibrate the emission line flux accurately. Therefore, we have developed a new method to restore Paα emission-line flux from ground-based narrow-band filter imaging observations. First, average atmospheric transmittance within the narrow-band filter is derived using 2MASS stars in a image. Second, PWV is then estimated by comparing the transmittance with that calculated by atmospheric transmittance model software, ATRAN. Finally, the atmospheric transmittance at the wavelength of Paα emission-line is obtained from the model atmosphere corresponding to the obtained PWV. By applying this method to the data of nearby Luminous Infrared Galaxies obtained by ANIR, the emission line strength is estimated within the accuracy of 10% relative to that observed by HST/NICMOS. In this paper, we describe details of the calibration method and its accuracy.
SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph) is one of the first-generation instruments
for the University of Tokyo Atacama Observatory (TAO; P.I.: Yuzuru Yoshii) 6.5-m telescope which is
planned to be constructed at the world's highest site, the summit of Cerro Chajnantor (an altitude of 5,640
m or 18,500 ft) in northern Chile. By placing a dichroic mirror into the collimated beam, SWIMS is capable
of wide-field (φ 9'.6 with 0".126 pixel-1) two-color simultaneous imaging as well as multi-object spectroscopy
(MOS) using cooled multi-slit masks covering the entire near-infrared spectra between 0.9 and 2.5 μm in a single
exposure with low-to-medium spectral resolutions. Up to 20 user-defined slit masks as well as long slit masks are
available. The field of view is covered with four 2048 x 2048 pixel HgCdTe focal plane arrays (HAWAII-2RG).
Tests of the MOS slit mask exchanger motions have been completed successfully without any trouble under
cryogenic environment. Further MOS tests will be performed at various tilt and rotation angles of the instrument
using a telescope simulator. Also, a conceptual study of a compact and cryogenic wide-field integral field
spectroscopy unit handled by the slit mask exchanger is now being carried out. The part of the current designs is
optimized for installation on the Subaru Telescope for performance verification and early scientific observations
prior to the construction of the TAO 6.5-m telescope. In this paper, we present the design and development
status of the instrument.
We are developing an integral field unit (IFU) for a near-infrared multi-object imaging spectrograph SWIMS
(Simultaneous-color Wide-field Infrared Multi-object Spectrograph). SWIMS is an instrument for the 6.5m
telescope of the University of Tokyo Atacama Observatory (TAO) project on the summit of Co. Chajnantor
(altitude of 5,640m) in northern Chile. Most of near infrared integral field spectrographs (IFSs) on 8–10m class
telescopes are used with adaptive optics and have fine spatial sampling. Compared with them, SWIMS IFU
has higher sensitivity for extended objects because it has coarser spatial sampling optimized for seeing-limit
observations. We have investigated the feasible optical design, and found a possible layout whose field of view
is about 14 x 10 arcsec2 with 0.4 arcsec slice width. All IFU mirror arrays will be made of aluminum alloy to
match the thermal expansion with support structures, as they are placed in a cryogenic environment. They will
be fabricated monolithically with high precision machining to reduce alignment process. We have carried out a
fabrication test of a spherical surface and confirmed that surface roughness and surface figure error are enough
low for near-infrared light. As a next step, fabrication of a prototype mirror array with 3 reflective surfaces is
planned. In this paper, we will show our project outline, the IFU optical design and the results of prototyping
works.
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