This paper describes a Cooled Infrared Spectrograph and Camera for OHS (CISCO), mounted on the Nasmyth focus of the Subaru telescope. It is primarily designed as a back-end camera of the OH-Airglow Suppressor (OHS), and is also used as an independent, general-purpose near-infrared camera/spectrograph. CISCO is based on a single 1024×1024 format HgCdTe HAWAII array detector, and is capable of either wide-field imaging of 1. ′ 8×1. ′ 8 field-of-view or low-resolution spectroscopy from 0.9 to 2.4 µm. The limiting magnitudes measured during test observations were found to be J = 23.5 mag and K ′ = 22.4 mag (imaging, 1 ′′ aperture, S/N = 5, 1 hr exposure).

This paper describes the first light and subsequent test observations with the 8.2 m aperture Subaru Telescope constructed at the summit of Mauna Kea. Following the engineering first light, which started 1998 December, the astronomical first light and test observations were carried out in 1999 January with 4 testing instruments under seeing conditions of 0″.2*#x2013;0″.5 for near-infrared and 0″.3–0″.6 for optical wavelengths. The actively supported primary mirror was shown to achieve an overall imaging performance of 0″.1 (FWHM) or better in the absence of any atmospheric disturbance. The pointing accuracy of the telescope is about 1″ rms, and a closed-loop tracking accuracy of ≲ 0″.07 rms has been achieved. Infrared images of the Orion Nebula covering 5′ × 5′, obtained with J, K″, and H2v = 1–0 S(1) filters, have revealed much finer and fainter details of the BN/KL region, the bright bar, and other conspicuous features compared with previous observations. K′ band photometry of 516 point sources yielded a luminosity function with a peak at K′ ∼ 12 mag with a long tail in K′ ∼ 13 mag down to K″ ∼ 17 mag, suggesting a fairly large number of young brown dwarfs existing in the Trapezium cluster. Several new features around the Orion BN/KL region are also reported.

Deep near-infrared images of a blank 2$^{\prime}$$ \times$ 2$ ^{\prime}$ section of sky near the galactic north pole taken by Subaru Telescope are presented. The total integration times of the $ J$ and $ K^{\prime}$ bands were 12.1 hr and 9.7 hr, resulting in 5$ \sigma$ limiting magnitudes of 25.1 and 23.5 mag, respectively. The numbers of sources within these limiting magnitudes found with an automated detection procedure are 385 in the $ J$ band and 350 in $ K^{\prime}$. Based on photometric measurements of these sources, we present number count vs. magnitude relations, color vs. magnitude diagrams, size vs. color relationships, etc. The slope of the galaxy number count plotted against the AB magnitude scale is about 0.23 in the 22 to 26 AB magnitude range of both bands. The spatial number density of galaxies as well as the slopes in the faint-end region given by the Subaru Deep Field (SDF) survey are consistent with those given by HST-NICMOS surveys, as expressed on the AB magnitude diagram. Several sources having very large $ J - K^{\prime}$ color have been found, including a few $ K^{\prime}$ objects without detection at $ J$. In addition, a number of faint galactic stars were also detected, most of which are assigned to M-subdwarfs, together with a few brown dwarf candidates.

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 µm. 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 (λ/∆λ = 210, S/N = 5) in the standard 4000 s exposure sequence.

High-resolution near-infrared J-band imaging with the Subaru Telescope has demonstrated, for the first time from the ground, two independent jets emanating from the protostar L 1551 IRS 5. Successive near-infrared spectroscopy has revealed that the jet emission is dominated by [FeII] lines in the J- and H-bands. While the visual-extinction estimated from the [FeII] line ratios reaches more than 20 mag in the close vicinity of IRS 5, it decreases rapidly at ∼ 1″ from IRS 5 and remains constant around 7 mag at larger distances. The electron density in the jets is estimated to be 106 cm−3 near IRS 5 and is 104 to 105 cm−3 in their outer section. The twisted appearance of the jets, with bright knots especially prominent in the northern jet, is similar to the R-band jets observed with the Hubble Space Telescope. These results suggest that the twisted structure and bright emission knots are intrinsic to the jets and are not due to a spatial variation of the extinction.