GMTNIRS: The Giant Magellan Telescope Near Infrared Spectrograph
GMTNIRS is high resolution near infrared spectrograph selected as a first generation instrument for the Giant Magellan Telescope (GMT). The conceptual design study for the instrument was completed in Fall 2011. In a single exposure, GMTNIRS will achieve spatial resolution of R = λ/Δλ = 65,000 in J, H, and K (1.07 – 2.45 μm), and with R = λ/Δλ = 85,000 in the L1, L2, and M bands (2.9 – 5.3 μm) with a K-band slit viewing camera for target acquisition. The instrument will exploit the adaptive optics (AO) capabilities of the GMT.
Figure 1. Optical path showing the GMTNIRS/MagNIFIES entrance window, input optics including the f/11 collimator and K- mirror, slit, and spectrographs. The slit-viewing camera is also shown. Following the slit are the six spectrographs and six cameras and detectors.
GMTNIRS takes advantage of the properties silicon immersion gratings as the primary diffractive elements. Silicon immersion gratings improve performance and reduce spectrograph size by taking advantage of the high index of refraction (3.4) of silicon to increase dispersion and allow extensive wavelength coverage at high resolution in a single exposure by permitting operation in high order.
Figure 2. Detailed layout of the J, H, and K modules of GMTNIRS showing the immersion gratings in green, which will be the primary dispersers, and the volume phase holographic gratings, which will provide cross-dispersion.
GMTNIRS is a collaboration between the University of Texas at Austin, The Korea Astronomy and Space Science Institute, and Kyung Hee University. GMTNIRS will be commissioned as the Magellan Near-IR Five-band Immersion grating Efficient Spectrograph (MagNIFIES), in a partnership with The Carnigie Institution. This will allow it to be deployed to GMT as a calibrated instrument with an experienced user community.
GMTNIRS/MagNIFIES will have the largest simultaneous spectral grasp of any high resolution spectrograph in the world in a single exposure: the entire spectrum transmitted through the Earth’s atmosphere from 1.07 – 5.3 μm.
Figure 3. Spectral grasp of GMTNIRS (blue) for a single exposure compared to other high-resolution near-infrared spectrographs currently or soon to be in use.
Figure 4. Some of the immersion gratings surfaces manufactured for the GMTNIRS instrument. The smaller gratings will be used in the J, H, and K channels (1.1 – 2.5 μm) and the larger gratings will be used in the L1, L2, and M channels (2.9 – 5.3 μm). We are looking at the blazed grating surface rotated to the Littrow configuration, at which the angle that light incident on the grating is reflected back in the direction from which it came.
Publications
Daniel T. Jaffe, Stuart Barnes, Cynthia Brooks, Hanshin Lee, Gregory Mace, Soojong Pak, Byeong-Gon Park, Chan Park, "GMTNIRS: progress toward the Giant Magellan Telescope near-infrared spectrograph", Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 990821 (9 August 2016); doi: 10.1117/12.2232994; https://doi.org/10.1117/12.2232994
Daniel T. Jaffe, Stuart Barnes, Cynthia Brooks, Michael Gully-Santiago, Soojong Pak, Chan Park, Insoo Yuk, "GMTNIRS (Giant Magellan Telescope Near-Infrared Spectrograph): optimizing the design for maximum science productivity and minimum risk", Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 914722 (28 July 2014); doi: 10.1117/12.2057084; https://doi.org/10.1117/12.2057084
D. T. Jaffe, D. J. Mar, D. Warren, P. R. Segura, "GMTNIRS: the high resolution near-IR spectrograph for the Giant Magellan Telescope", Proc. SPIE 6269, Ground-based and Airborne Instrumentation for Astronomy, 62694I (29 June 2006); doi: 10.1117/12.672148; https://doi.org/10.1117/12.672148