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The Immersion Grating Infrared Spectrometer (IGRINS) is a revolutionary instrument that exploits broad spectral coverage at high-resolution in the near-infrared. IGRINS employs a silicon immersion grating as the primary disperser, and volume-phase holographic gratings cross-disperse the H and K bands onto Teledyne Hawaii-2RG arrays. The use of an immersion grating facilitates a compact cryostat while providing simultaneous wavelength coverage from 1.45 - 2.5 μm. There are no cryogenic mechanisms in IGRINS and its high-throughput design maximizes sensitivity. IGRINS on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory is nearly as sensitive as CRIRES at the 8 meter Very Large Telescope. However, IGRINS at R≈45,000 has more than 30 times the spectral grasp of CRIRES* in a single exposure. Here we summarize the performance of IGRINS from the first 300 nights of science since commissioning in summer 2014. IGRINS observers have targeted solar system objects like Pluto and Ceres, comets, nearby young stars, star forming regions like Taurus and Ophiuchus, the interstellar medium, photo dissociation regions, the Galactic Center, planetary nebulae, galaxy cores and super novae. The rich near-infrared spectra of these objects motivate unique science cases, and provide information on instrument performance. There are more than ten submitted IGRINS papers and dozens more in preparation. With IGRINS on a 2.7m telescope we realize signal-to-noise ratios greater than 100 for K=10.3 magnitude sources in one hour of exposure time. Although IGRINS is Cassegrain mounted, instrument flexure is sub-pixel thanks to the compact design. Detector characteristics and stability have been tested regularly, allowing us to adjust the instrument operation and improve science quality. A wide variety of science programs motivate new tools for analyzing high-resolution spectra including multiplexed spectral extraction, atmospheric model fitting, rotation and radial velocity, unique line identification, and circumstellar disk modeling. Here we discuss details of instrument performance, summarize early science results, and show the characteristics of IGRINS as a versatile near-infrared spectrograph and forerunner of future silicon immersion grating spectrographs like iSHELL2 and GMTNIRS.3
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