GMTNIRS, the Giant Magellan Telescope near-infrared spectrograph, is a first-generation instrument for the GMT that will provide detailed spectroscopic information about young stellar objects, exoplanets, and cool and/or obscured stars. The optical and mechanical design GMTNIRS presented at a conceptual design review in October 2011 covered all accessible parts of the spectrum from 1.12 to 5.3 microns at R=50,000 (1.12-2.5 microns) and R=100,000 (3-5.3 microns). GMTNIRS uses the GMT adaptive-optics system and has a single 85 milliarcsecond slit. The instrument includes five separate spectrographs for the different atmospheric windows. By use of dichroics that divide the incident light between five separate spectrographs, it observes its entire spectral grasp in a single exposure while having only one cryogenic moving part, a rotating pupil stop. Large, highly accurate silicon immersion gratings are critical to GMTNIRS, since they both permit a design within the allowable instrument volume and enable continuous wavelength coverage on existing detectors. We describe the effort during the preliminary design phase to refine the design of the spectrograph to meet the science goals while minimizing the cost and risk involved in the grating production. We discuss different design options for the individual spectrographs at R=50,000, 67,000, 75,000, and 100,000 and their impact on science return.

Date Published: 28 July 2014
PDF: 10 pages
Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 914722 (28 July 2014); doi: 10.1117/12.2057084

Published in SPIE Proceedings Vol. 9147:
Ground-based and Airborne Instrumentation for Astronomy V
Suzanne K. Ramsay; Ian S. McLean; Hideki Takami, Editor(s)