A new design for an aberration-corrected concave grating for the spectral region near 10 microm is presented. It was designed for use in the ground-based astronomical medium-resolution (lambda/Dlambda approximately 100) Mid-Infrared Camera and Spectrometer (MICS). It provides a flat focal plane for a wide spectral range (7.5-13.5 microm) with small aberrations, permitting efficient long-slit observations in the mid-infrared region. It permits a simple design of the spectrometer without collimator and camera mirrors, which is quite advantageous for cryogenic instruments. The grating has variable spacing grooves to reduce aberrations. In addition, the grating surface figure is designed to be toroidal and in the direction perpendicular to the grooves, aspherical, to suppress the aberrations further over a wide spectral range. The angle of the grooves is also varied to yield better efficiency near the blaze angle. The grating was fabricated by high-quality ultraprecision machining, which made these features possible. Test observations confirmed that the designed spectral resolution was achieved.

Collimator

Spectral resolution

Imaging spectrometer

Slit

Curved mirror

10.1364/ao.39.001474

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Citations (8)

High‐Resolution Mid‐Infrared Imaging and Spectroscopic Observations of a Massive Star Forming Region W51 IRS 2

The Astrophysical Journal (2001)

Y. Okamoto Hirokazu Kataza Takuya Yamashita Takashi Miyata Takashi Onaka

Mid-infrared (7.8-13.5μm) imaging and low-resolution spectroscopic observations were made for the massive star-forming region W51 IRS 2 with spatial resolution of 1''. IRS 2 was resolved into seven sources based on the continuum and the emission line maps. The nature of these sources was investigated using their thermal dust emission, the 9.7 μm absorption feature, and/or three fine-structure emission lines of [Ne II] at 12.8 μm, [Ar III] at 8.99 μm, and [S IV] at 10.51 μm. Four of the sources were identified as ultracompact H II regions and one as an embedded protostar candidate. The spectral types of the ionizing sources are derived from the line ratios to be all around O9, which is much later than those (O5.5 and O7.5) derived from the radio continuum fluxes. The observed line ratios of (ultra-)compact H II regions in IRS 2 and in the literature follow a single excitation track, but it is different from that predicted from model calculations. We propose two possible resolutions for the discrepancy: (1) the employed models for the stellar atmosphere are not sufficiently accurate in the UV range, or (2) the (ultra-)compact H II regions are ionized by stellar clusters.

Protostar

H II region

Line (geometry)

Spectral resolution

10.1086/320633

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Citations (31)

MAXI/GSC detection of 4th renewed activity of the distant Z-source MAXI J0556-332

The astronomer's telegram (2020)

H. Negoro T. Yoshitake M. Nakajima M. Aoki K. Kobayashi

Source

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