High Resolution Spectrograph Unit (HRU) for the Subaru/IRCS

摘要

We present an upgrade plan of the infrared camera, and spectrograph for the Subaru Telescope (IRCS~(1-4)) to introduce the high resolution spectroscopic mode (a resolving power; R=λ/△λ > 70,000) in the infrared bands (1.4-5.5μm). To realize the compact and stable cooled instrument, we are developing the immersion grating5 with Si whose refractive index is ～ 3.4. The optics design is significantly compact (600mm × 250mm × 250mm) using the Si immersion grating, and it can be easily located beside or inside the IRCS main dewar. The IRCS has been operating for 8 years with an extremely stable condition, and it is combined with the next generation adaptive optics system (AO188~6) and the laser guide star system (LGS~7) of the Subaru Telescope. The quick integration of the new high resolution spectrograph unit (HRU) can be expected by using the existing stable instrument. The total performance with the designed optics is so good that the optical design could meet the required specifications. The image quality shows a strehl ratio of > 0.88 for the entire bands, and 24 scannings of the gratings can cover the 1.4-5.5μm. We plan to fabricate the Si immersion grating for the actual astronomical use in 2009, and the HRU will be built around 2011. It will be the first high sensitive infrared spectrograph with high spectral resolution capability in the northern hemisphere and with the laser guide star AO system.