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
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
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.
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:
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