Mid-infrared High-resolution Spectrograph for SPICA

摘要

We present a preliminary optical design and layout for the mid-infrared (4-18μm) high-resolution spectrograph for SPICA, Japanese next-generation space IR observatory with 3.5 m telescope. MIR high-resolution spectroscopy is a powerful probe to study gas-phase molecules/atoms in a variety of astronomical objects. Space observation provides a great opportunity to study many molecular lines especially in between the atmospheric windows. SPICA gives us a chance to realize MIR high-resolution spectroscopy from space with the large telescope aperture. The major technical challenge is the size of the spectrograph, which tends to be too large for space. We hope to overcome this problem with a novel MIR immersion grating, which can make the instrument smaller by a factor of the refractive index of the grating material. We plan to fabricate a large pitch ZnSe (n = 2.4) immersion grating with the fly-cutting technique at LLNL (see Poster paper 7018-183 by Ikeda et al. and 7018-181 by Kuzmenko et al. in the proceedings of this conference). We show our preliminary spectrograph designs with a spectral resolution of ～30,000 in 4-8μm (short mode) and 12-18μm (long mode). The instrument size can be as small as 200×400 mm thanks to the MIR immersion gratings. With unprecedented spectral resolution in space, which is 10-times higher than ISO-SWS, the high-resolution spectrograph for SPICA (SPICA-HIRES) could be a unique instrument that can provide most sensitive and clear spectra of this kind.