The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI 1 satellite. It is designed for wide-field deep imaging and low-resolution spectroscopy in the near-to mid-infrared (1.8-26.5 µm) in the pointed observation mode of AKARI. IRC is also operated in the survey mode to make an all-sky survey at 9 and 18 µm. It comprises three channels. The NIR channel (1.8-5.5 µm) employs a 512 × 412 InSb array, whereas both the MIR-S (4.6-13.4 µm) and MIR-L (12.6-26.5 µm) channels use 256 × 256 Si:As impurity band conduction arrays. Each of the three channels has a field-of-view of about 10 ′ × 10 ′ and are operated simultaneously. The NIR and MIR-S share the same field-of-view by virtue of a beam splitter. The MIR-L observes the sky about 25 ′ away from the NIR/MIR-S field-of-view. IRC gives us deep insights into the formation and evolution of galaxies, the evolution of planetary disks, the process of star-formation, the properties of interstellar matter under various physical conditions, and the nature and evolution of solar system objects. The in-flight performance of IRC has been confirmed to be in agreement with the pre-flight expectation. This paper summarizes the design and the in-flight operation and imaging performance of IRC.

Classical Cepheids are useful tracers of the Galactic young stellar population because their distances and ages can be determined from their period-luminosity and period-age relations. In addition, the radial velocities and chemical abundance of the Cepheids can be derived from spectroscopic observations, providing further insights into the structure and evolution of the Galaxy. Here, we report the radial velocities of classical Cepheids near the Galactic Center, three of which were reported in 2011, the other reported for the first time. The velocities of these Cepheids suggest that the stars orbit within the Nuclear Stellar Disk, a group of stars and interstellar matter occupying a region of ∼ 200 pc around the Center, although the three-dimensional velocities cannot be determined until the proper motions are known. According to our simulation, these four Cepheids formed within the Nuclear Stellar Disk like younger stars and stellar clusters therein.

We report a newly developed spectropolarimeter with a low-dispersion resolution (R \ 40È 200) and a wide coverage in wavelength (400È900 nm). It is mainly used along with the 0.91 m telescope at the Dodaira Observatory of the National Astronomical Observatory, Japan. This instrument and the related reduction software are described brieÑy. The present polarimetric accuracy (rms) is estimated to be [(P/ 50)2 ] (0.05)2]1@2%, where P is the linear polarization degree in percent. The spectropolarimeter has the advantage of being most useful in the polarimetric studies of both the continuum and the strong emission and/or absorption lines. It is mainly used for the short-or long-term monitoring of variable circumstellar polarization and of polarization in comets, and for studies on interstellar polarization.

The Infrared Camera (IRC) is one of the two instruments on board the AKARI satellite. In addition to deep imaging from 1.8-26.5µm for the pointed observation mode of the AKARI, it has a spectroscopic capability in its spectral range. By replacing the imaging filters by transmission-type dispersers on the filter wheels, it provides low-resolution (λ/δλ ∼ 20-120) spectroscopy with slits or in a wide imaging field-of-view (approximately 10 ′ ×10 ′ ). The IRC spectroscopic mode is unique in space infrared missions in that it has the capability to perform sensitive wide-field spectroscopic surveys in the near-and midinfrared wavelength ranges. This paper describes specifications of the IRC spectrograph and its in-orbit performance.

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