The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is developed as the first-generation mid-infrared instrument for the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU performs medium-band imaging and low-resolution spectroscopy in 2-38 microns and enables highest-spatial-resolution observations in the long-wavelength mid-infrared beyond 25 microns. In addition, MIMIZUKU has a unique opto-mechanical device called ‘Field Stacker’, which enables us to observe a distant (<25 arcminutes) pair of target and reference objects simultaneously and improves accuracy of atmospheric calibration. This function is expected to improve photometric accuracy and quality of spectroscopic data even in the long-wavelength mid-infrared regions, where the atmospheric absorption is severe. In 2018, engineering observations of MIMIZUKU were carried out at the Subaru telescope, and its first-light was successfully achieved. In the engineering observations, the imaging and spectroscopic functions in the mid-infrared wavelengths (7.6-25 microns) were confirmed to be working almost as expected, although the sensitivity is still worse than the background-limited performance by a factor of a few due to high readout noise. The Field Stacker was also confirmed to be working as expected. It is confirmed that the photometric instability can be reduced to a few percent by using Field Stacker even when the atmospheric transmittance varies by 10% in time. It is also confirmed that spectroscopic observations can be performed not only in 10-micron band but also in 20-micron band, where the spectroscopic observations are difficult even at the Mauna Kea site. We report the results of these on-sky performance evaluations.
We are developing an image-slicer type integral field unit (IFU), SWIMS-IFU, for SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph), a near-infrared instrument for TAO 6.5 m telescope. SWIMS- IFU divides a field-of-view of 16:006 12:008 into 26 slices with a width of 0:005, which is the largest FoV among near-infrared IFUs on 8 m class telescopes. It is also capable of obtaining entire near-infrared spectra from 0.9 to 2.5 m with R1000 with a single exposure. Because of limitations of space in SWIMS, SWIMS-IFU should fit in a volume of 170 x 220 x 60 mm3, which results in small and complicatedly aligned mirror facets. To reduce alignment procedures, we adopt an ultra-precision cutting technique to fabricate mirror arrays monolithically. We have completed one of the mirror arrays, the slit-mirror array which consists of 26 spherical mirror facets, and confirmed both their surface roughness and shape errors satisfy the requirements. We also have fabricated a prototype of the pupil-mirror array including some elliptical mirror facets and confirmed that the elliptical mirrors have enough surface qualities and produce better image quality than spherical ones by a pinhole imaging test.
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.
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