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
IGRINS (Immersion GRating INfrared Spectrometer) is a high resolution wide-band infrared spectrograph developed by the Korea Astronomy and Space Science Institute (KASI) and the University of Texas at Austin (UT). This spectrograph has H-band and K-band science cameras and a slit viewing camera, all three of which use Teledyne's λc~2.5μm 2k×2k HgCdTe HAWAII-2RG CMOS detectors. The two spectrograph cameras employ science grade detectors, while the slit viewing camera includes an engineering grade detector. Teledyne's cryogenic SIDECAR ASIC boards and JADE2 USB interface cards were installed to control those detectors. We performed experiments to characterize and optimize the detector systems in the IGRINS cryostat. We present measurements and optimization of noise, dark current, and referencelevel stability obtained under dark conditions. We also discuss well depth, linearity and conversion gain measurements obtained using an external light source.
The Immersion Grating Infrared Spectrometer (IGRINS) is a compact high-resolution near-infrared cross-dispersed
spectrograph whose primary disperser is a silicon immersion grating. IGRINS covers the entire portion of the
wavelength range between 1.45 and 2.45μm that is accessible from the ground and does so in a single exposure with a
resolving power of 40,000. Individual volume phase holographic (VPH) gratings serve as cross-dispersing elements for
separate spectrograph arms covering the H and K bands. On the 2.7m Harlan J. Smith telescope at the McDonald
Observatory, the slit size is 1ʺ x 15ʺ and the plate scale is 0.27ʺ pixel. The spectrograph employs two 2048 x 2048
pixel Teledyne Scientific and Imaging HAWAII-2RG detectors with SIDECAR ASIC cryogenic controllers. The
instrument includes four subsystems; a calibration unit, an input relay optics module, a slit-viewing camera, and nearly
identical H and K spectrograph modules. The use of a silicon immersion grating and a compact white pupil design allows
the spectrograph collimated beam size to be only 25mm, which permits a moderately sized (0.96m x 0.6m x 0.38m)
rectangular cryostat to contain the entire spectrograph. The fabrication and assembly of the optical and mechanical
components were completed in 2013. We describe the major design characteristics of the instrument including the
system requirements and the technical strategy to meet them. We also present early performance test results obtained
from the commissioning runs at the McDonald Observatory.
IGRINS, the Immersion GRating INfrared Spectrometer, is a near-infrared wide-band high-resolution spectrograph
jointly developed by the Korea Astronomy and Space Science Institute and the University of Texas at Austin. IGRINS
employs three HAWAII-2RG focal plane array (FPA) detectors. The mechanical mounts for these detectors and for the
final (field-flattening) lens in the optical train serve a critical function in the overall instrument design: Optically, they
permit the only positional compensation in the otherwise “build to print” design. Thermally, they permit setting and
control of the detector operating temperature independently of the cryostat bench. We present the design and fabrication
of the mechanical mount as a single module. The detector mount includes the array housing, housing for the SIDECAR
ASIC, a field flattener lens holder, and a support base. The detector and ASIC housing will be kept at 65 K and the
support base at 130 K. G10 supports thermally isolate the detector and ASIC housing from the support base. The field
flattening lens holder attaches directly to the FPA array housing and holds the lens with a six-point kinematic mount.
Fine adjustment features permit changes in axial position and in yaw and pitch angles. We optimized the structural
stability and thermal characteristics of the mount design using computer-aided 3D modeling and finite element analysis.
Based on the computer simulation, the designed detector mount meets the optical and thermal requirements very well.