Design and status of a near-infrared multi-object spectrograph for the TAO 6.5-m telescope

We describe the design and current status of a near-infrared multi-object spectrograph for the University of Tokyo Atacama Observatory (TAO) project, which is to construct a 6.5m infrared telescope on the summit of Co. Chajnantor (altitude of 5,460m) in the northern Chile. The instrument, named SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph), covers a wavelength range from 0.9 to 2.5 μm with a field of view of 9.6 in diameter using 4096 x 4096 pixels with a pixel scale of 0.″13 pixel^-1. It has two observation modes: a wide-field imager and a multi-object spectrograph (MOS). The MOS mode adopts cooled multi-slit masks with 30 slits at a maximum, and achieves a spectral resolution of λ/Δλ∼ 1000. Up to 20 masks can be installed in a mask storage dewar. In both modes, two wavelength ranges of 0.9-1.4 μm and 1.4-2.5 μm are observed simultaneously with a dichroic mirror placed in the collimated beam. This will provide us data covering the wide spectral range under same conditions such as weather, telescope pointing, and so on. Such data are important not only for redshift surveys of distant galaxies but also for rapidly time-variable events such as gamma-ray bursts. As SWIMS is expected to be completed before the construction of the 6.5m telescope, we plan to carry out performance verification and early scientific observations on the Subaru Telescope at Hawaii.