Line survey observation of circumstellar envelope of late type stars

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We have developed the "mid-infrared high dispersion spectrograph" (IRHS), a cryogenic echelle spectrometer designed for Nasmyth focus stage of NAOJ Subaru 8.2m telescope, which operate at 8-13μm in wavelength with the resolving power λ/Δλ of 〜44,000 at 10μm. In order to achieve high dispersion, broad bandwidth and high sensitivity, two key devices are employed : a single crystal germanium immersion echelle grating (30 x 30 x 72mm) and a Si:As IBC (Impurity band conductor) array detector (412 x 512 pixels, unit pixel size 30μm) operated at 5K. The germanium immersion echelle grating for collimated beam size of 28mmφ was fabricated by utilizing ultra precision micro-grinding method coupled with "ELectrolytic In-process Dressing" (ELID) technique. To reduce thermal radiation of the instrument, all optics of IRHS is arranged on the cold optical base plate (〜30K) of the cryostat with the diameter of 80cm. The simple optical design will enable rapid wavelength scan in 8-13μm region, and will be most powerful equipment for the detailed astronomical search of new interstellar molecular spectra.In April 2005, we carried out the first light observation of IRHS at MITAKA 1.5m telescope of NAOJ, Tokyo. By conducting the long-term continues observations (〜1 month) of 19 infrared bright objects, the performance of slit viewer optics was evaluated. As a result of the evaluations, the limited magnitude and the efficiency were estimated to be 7.1mag. (1.0 sec, S/N=10, Seeing:1.0 arcsec) and 50% respectively.