IGRINS: Immersion Grating Infrared Spectrometer
IGRINS, the Immersion Grating INfrared Spectrometer, is an extremely powerful and unique instrument that obtains both broad spectral coverage and high spectral resolution. IGRINS is a cross-dispersed near-IR spectrograph with a resolving power R=λ/Δλ = 45,000 (Yuk et al. 2010, Park et al. 2014). It can observe the entire H and K windows, from 1.45 to 2.5 microns, in a single exposure. This coverage represents a revolutionary increase in spectral grasp (instantaneous spectral coverage) at high resolution enabled by the use of a silicon immersion echelle grating and two 2Kx2K infrared detectors. IGRINS has also been optimized for observers. IGRINS has an infrared slit-viewing camera for rapid acquisition in the K band. It has a single observing mode and no cryogenic moving parts. This simple design makes it easy for new observers to master and allows the instrument team to provide a simple data reduction pipeline. The pipeline is primarily authored by Dr. Jae-Joon Lee (KASI) and is publicly available. By making use of the latest low-noise detectors, a silicon immersion grating, and volume-phase holographic (VPH) cross-dispersers, IGRINS has the sensitivity to attack a broad range of astronomical problems (see Astronomy with IGRINS) at its principal site, the 2.7m Harlan Smith Telescope at McDonald Observatory. At McDonald, the instrument sits at the Cassegrain focus of the 2.7 meter and the slit size is 1”x14”, with 3.5 pixel sampling across the slit. Further technical details are available in Yuk et al. (2010) and Park et al. (2014).
IGRINS has thus far had over 350 nights of observations at McDonald Observatory since its commissioning in the summer of 2014. Currently, IGRINS is also under contract with the 4.3m Discovery Channel Telescope at Lowell Observatory, and will be moving between the DCT and the 2.7m Harlan Smith Telescope at McDonald Observatory over the next three years (2016-2019). After a successful commissioning at the 4.3m DCT, we see about a magnitude gain, which is essential in accessing faint targets.
IGRINS is a collaboration of the University of Texas, the Korea Astronomy and Space Science Institute KASI. Prof. Daniel Jaffe of UT Austin is the IGRINS PI. Dr. Chan Park of KASI is deputy PI and KASI instrument PI. Dr. Jae-Joon Lee at KASI supervises the IGRINS operational program on the Korean side.
IGRINS is a PI instrument and is open for use to anyone who obtains time at McDonald Observatory or the DCT, with the restriction that a member of the instrument team should be included in any proposal.
For further information please see the instrument page (http://www.as.utexas.edu/mcdonald/
Figure 1: Optical layout for IGRINS. All parts shown are within the cryogenic part of the instrument.
Figure 2:(left) K-band echellogram. The box shows the 2048 array. The dashed lines give the nominal ends of the orders. The order spacings on the right are for a 4m telescope. (right) Spot diagrams for the H band. The boxes are 2x2 pixels. The slit width is 3.6 pixels.
Figure 3: CAD drawing of the IGRINS optical bench. The longest dimension is ~0.9m. Light enters at top center. The immersion grating is in the pink housing at the center and the H and K band detectors are at the lower left and right.
Figure 4: IGRINS optical bench during test assembly. The H and K band cameras and detectors are in the foreground.