‘Field Stacker’ is a unique system mounted on MIMIZUKU, a mid-infrared instrument for the TAO 6.5-m telescope. This system obtains a pair of distant targets simultaneously and aims at performing relative photometry with an accuracy of a few percent. A key to achieve the accurate relative photometry is precise flat fielding. We have developed a new method for the flat fielding using time variation of the sky background. We analyzed the data obtained in an engineering observation at the Subaru in 2018. The error of the flat fielding and the total error propagated from the flat fielding are estimated to be 0.2–0.3% and 0.5%, respectively.
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.
MIMIZUKU (Mid-infrared Multi-field Imager for gaZing at the UnKnown Universe) is a near- to mid-infrared camera for the 6.5-m TAO (The university of Tokyo Atacama Observatory) telescope. To realize both the compactness of the instrument and the wide field of view of 2 arcmin, MIMIZUKU has unique reflective optics, which is composed of off-axis aspherical mirrors made of machined aluminum. These mirrors should be placed and aligned very precisely with the accuracy of < 0.01 mm and < 0.01 degrees. We performed the experiments to test whether MIMIZUKU optics works as designed at cryogenic temperature. We present the evaluation of imaging performance and the distortion on the focal plane of MIMIZUKU.
The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is a mid-infrared camera and spectrograph developed as a first-generation instrument on the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU covers a wide wavelength range from 2 to 38 μm and has a unique optical device called Field Stacker which realizes accurate calibration of variable atmospheric transmittance with a few percent accuracy. By utilizing these capabilities, MIMIZUKU realizes mid-infrared long-term monitoring, which has not been challenged well. MIMIZUKU has three optical channels, called NIR, MIR-S, and MIR-L, to realize the wide wavelength coverage. The MIR-S channel, which covers 6.8–26 μm, has been completed by now. We are planning to perform engineering observations with this channel at the Subaru telescope before the completion of the TAO 6.5-m telescope. In this paper, we report the results of the laboratory tests to evaluate the optical and detector performances of the MIR-S channel. As a result, we confirmed a pixel scale of 0.12 arcsec/pix and a vignetting- free field of view of 2./0 1./8. The instrument throughputs for imaging modes are measured to be 20–30%. Those for N - and Q -band spectroscopy modes are 17 and 5%, respectively. As for the detector performance, we derived the quantum efficiency to be 40–50% in the mid-infrared wavelength region and measured the readout noise to be 3000–6000 electrons, which are larger than the spec value. It was found that this large readout noise degrades the sensitivity of MIMIZUKU by a factor of two.
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.
Time variation of the atmospheric water vapor is an important problem to achieve accurate photometry in ground-based mid-infrared observations. Long-term (~ minutes or hours) variation has been already known, but short-term (~ seconds) variation has not been quantified in previous studies. We evaluate this short-term variation and the photometric error in the mid-infrared observations at the TAO site by using actual astronomical data. Estimated photometric errors are typically less than 1% but show 2-5% in two of fifteen cases. This suggests that the short-term variation of the water vapor is one of the factors which limit the photometric accuracy in ground based mid-infrared observations.
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