Near-INfrared and optical Joint spectrograph with Adaptive optics (NINJA) is an optical to near-infrared (NIR) spectrograph optimized for the laser tomography adaptive optics (LTAO) system at the Subaru telescope, realized by the adaptive secondary mirror and four-laser guide star (LGS) system now under development. One of the primary science objectives of this spectrograph is wide-band spectroscopic follow-up of transient sources like GRB, supernovae, or gravitational wave sources down to 22 mag in the J -band. NINJA consists of two spectrograph units, one is in the optical (0.35-0.85 µm) and the other in the NIR (0.85-2.5 µm), and a fore-optics which splits the light from the telescope to the spectrographs and wavefront sensors (WFSs) of LTAO. Each spectrograph has a slit with 0.35′′ wide and 5′′ long, and a spectral resolution of R=3000-4000 utilizing a grating. The four LGSs are planned to be arranged on a circle around the slit with a radius of about 8′′, and a patrol field of view (FoV) of a tip-tilt guide star is about 2′ diameter. With two dichroic mirrors, the fore-optics splits the light of the FoV into three wavelength ranges of 0.35-0.85 µm, 0.85-2.5 µm, and 0.589 µm for LGS. In this paper, we report the overall system of NINJA and a conceptual design of the optics.
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