GMTNIRS (Giant Magellan Telescope Near-Infrared Spectrograph): optimizing the design for maximum science productivity and minimum risk

Abstract

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.

Design and early performance of IGRINS (Immersion Grating Infrared Spectrometer)

“…Unique features of IGRINS include the use of a silicon immersion echelle grating as the main disperser and volume phase holographic gratings as the cross-dispersers. 4,9 The entire optical design contains total nineteen powered lenses and seven mirrors including three aspherical off-axis aluminum collimating mirrors and two toroidal Infrasil field flattening lenses. The telescope focus is external to the cryostat.…”

The Giant Magellan Telescope adaptive optics program

“…The GMT si ed parameter r ng section desc esents the preli m, and Section ing Modes will support thr roaches to bala orrector for all e Ground Laye gorian field of ge quality imp e Natural Guide rument to prov ited imaging at e Laser Tomog tomographicall ection of a cent the first genera anned in 201 igned specifica MTNIRS 5 ). Th graph 7 will both on Cerro Camp ation for const the elements in vides facilities ite provides ex r 0 =16.4 cm.…”

Comb-resolved spectroscopy with immersion grating in long-wave infrared

“…In the field of infrared astronomy, immersion gratings are highly desired for their high resolving power, which for a normal echelle grating would have been of much larger sizes. Immersion gratings have been already installed on international telescopes [32][33][34].…”