Development of Multi-Object Spectroscopy Unit for Simultaneous-color Wide-field Infrared Multi-object Spectrograph

SWIMS (Simultaneous-color Wide-field Infrared Multi-object Spectrograph) has a multi-object spectroscopic function including IFU in addition to the imaging capability. The mechanics to achieve this function is MultiObject Spectroscopy Unit (MOSU), which consists of the slit-mask dewar (carrousel), the focal plane dewar, and the robotic arm called slit-mask exchanger. It allows us to derive spectra of 20-30 objects over a wavelength range from 0.9 to 2.5pm simultaneously using a slit-mask. It also handles a compact image slicer module mounted on the same mechanical interface as the slit-mask. To set or exchange a slit-mask on a telescope focal plane. There are many structural and mechanical features in MOSU to achieve its performance in cooling system, positional repeatability of slit-mask and so on. We present here its unique components and its specifications and performance.