OHS: OH-airglow Suppressor for the Subaru Telescope

This paper describes an OH-airglow Suppressor (OHS) for the infrared Nasmyth focus of the Subaru telescope. OHS has the capability of eliminating 224 airglow-lines in the $J$- and $H$-bands, which are major sources of background radiation at near-infrared wavelengths up to 2 $\mu$m. Specifically, it is a pre-optics system installed between the telescope and an infrared camera/spectrograph (CISCO). The suppressor reduces sky background emissions to 1/25 and its throughput is 40%. As a result, the S/N gain achieved with OHS is more than 1 mag compared to the typical spectroscopic approach. The limiting magnitude measured during a test observing run was found to be $H$ = 21.1 mag ($\lambda/\Delta\lambda$ = 210, S/N = 5) in the standard 4000 s exposure sequence.