MANIFEST is a fibre-fed positioning system designed to enhance the capabilities of the 24.5m Giant Magellan Telescope (GMT). For the first light 14 arcmin field-of-view (FoV), MANIFEST will use the GMT’s current planned instruments: G-CLEF (an echelle resolution spectrograph) and GMACS (low/mid resolution spectrograph). MANIFEST will connect with these existing optical spectrographs and offer three multiplexing and deployable integral field unit (IFU) modes. In the future, a full 20′ FoV mode will be offered using a near-infrared spectrograph. Its unique features include high multiplexing, deployable IFUs, increased spectral resolution, and the potential for simultaneous observations with multiple instruments. MANIFEST will support four key science cases: galactic archaeology, dynamical masses of local dwarf galaxies, galaxy stellar kinematics, and unveiling the reionisation epoch with Lyα. In addition, simulations comparing Starbugs, pick-and-place, Starspines, and Theta-phi positioning technologies determined that the pick-and-place robotic solution offers optimal performance, reliability, and adaptability while minimising technical risk with off-the-shelf components. MANIFEST’s advanced capabilities will ensure efficient survey operations and maximise scientific output, making it a pivotal tool for the GMT.
NIRMOS (Near-Infrared Multiple Object Spectrograph) is a 0.9 to 2.5 μm imager/spectrograph concept proposed for the
Giant Magellan Telescope1 (GMT). Near-infrared observations will play a central role in the ELT era, allowing us to
trace the birth and evolution of galaxies through the era of peak star formation. NIRMOS' large field of view, 6.5′ by
6.5′, will be unique among imaging spectrographs developed for ELTs. NIRMOS will operate in Las Campanas' superb
natural seeing and is also designed to take advantage of GMT's ground-layer adaptive optics system. We describe
NIRMOS' high-performance optical and mechanical design.
The Smithsonian Widefield Infrared Camera (SWIRC) is a Y -, J-, and H-band imager for the f/5 MMT.
Proposed in May 2003 and commissioned in June 2004, the goal of the instrument was to deliver quickly a wide
field-of-view instrument with minimal optical elements and hence high throughput. The trade-off; was to sacrifice
K-band capability by not having an internal, cold Lyot stop. We describe SWIRC's design and capabilities, and
discuss lessons learned from the thermal design and the detector mount, all of which have been incorporated into
the upcoming MMT & Magellan Infrared Spectrograph.
The Giant Magellan Telescope, with seven 8.4 meter primary mirrors, is taking shape as one of the most powerful
telescopes of the next generation. We describe a conceptual design for a powerful 0.85 to 2.50 μm imaging
spectrograph that addresses a 7' by 7' field of view for imaging and a 5' by 7' field of view for spectroscopy at the
GMT's f/8 Gregorian focus. The all-refractive optical design presses the limits of available lens blank diameters, but
delivers excellent images (~0.15" 80% encircled energy) with just four collimator elements and five camera elements.
The collimated beam diameter is 300 mm, and the detector is a 6K by 10K array. The spectrograph will use
interchangeable slit masks, and an assortment of VPH and conventional surface relief gratings. Each of the entire J, H,
or K bands can be observed with a resolution of 3000. The scientific potential of ground layer adaptive optics (GLAO)
using a constellation of sodium laser guide stars appears to be very high in the near infrared. Simulations suggest that
0.2" FWHM images may be achieved across the entire 7' by 7' field of view of the spectrograph. We describe the
design of the GLAO system with a versatile opto-mechanical design that allows rapid changeover between GLAO and
seeing-limited observations.
In 2003, the converted MMT’s wide-field f/5 focus was commissioned. A 1.7-m diameter secondary and a large refractive corrector offer a 1° diameter field of view for spectroscopy and a 0.5° diameter field of view for imaging. Stellar images during excellent seeing are smaller than 0.5" FWHM across the spectroscopic field of view, and smaller than 0.4" across the imaging field of view. Three wide-field f/5 instruments are now in routine operation: Hectospec (an R~1000 optical spectrograph fed by 300 robotically-positioned optical fibers), Hectochelle (an R~40,000 optical spectrograph fed by the same fibers), and Megacam (a 340 megapixel, 36 CCD optical imager covering a 25' by 25' format).
We have completed a detailed thermal analysis of Binospec, a wide-field, multi-slit spectrograph being developed for the 6.5m MMT. The goals of our analysis were to minimize temperature gradients and thermally-induced deflections and achieve a > 24 hr time constant in the spectrograph optics. We consider the effects of conduction, convection, and radiation with the external environment, and model the consequences of opening a spectrograph to insert new slit masks or filters. We study when internal heat sources balance environmental effects, and the local effects of a hot motor in a spectrograph. We review the results of these thermal analyses and draw general conclusions useful to instrument builders.
We describe our plans to add cross-dispersion and an integral field unit to the Hectochelle spectrograph, a multiobject, fiber-fed echelle spectrograph for the converted MMT. Hectochelle was originally designed without cross-dispersion to be used in a single order or overlapping orders selected by interference filters. The addition of cross-dispersion allows us to trae off multiplex advantage for spectral coverage. Our cross-disperser uses an unusual segmented, zero-deviation prism that is very compact, allowing it to fit into the existing instrument without modification. The planned integral field unit can be used with either Hectochelle or the moderate-dispersion Hectospec bench spectrograph. Both spectrographs were originally designed to be fiber-fed with a robotic fiber positioner as a front end, so adding an integral field capability is a natural enhancement. The integral field unit will use smaller diameter fibers than the robotic fiber positioner (subtending 0".6 vs. 1".5), so that both spectrographs will achieve higher spectral resolution in integral field mode. With the integral field unit Hectochelle will reach a two pixel resolution, R approximately 70,000, and Hectospec will reach R approximately 2000 with its 270 line mm-1 grating.
Binospec is a binocular optical spectrograph under development for the converted MMT. Binospec addresses two adjacent 8' by
15' fields of view, yielding an effective slit length of
30'. Despite its very wide field of view, Binospec's optics
are compact due to the favorable image scale at the converted MMT's
f/5 Cassegrain focus. However, Binospec's all-refractive collimator
and camera have presented several challenges, including the need for
careful athermalization and high performance optics mounts. In the
course of Binospec's development H.W.E. and D.G.F. developed a new
athermalization technique to maintain image scale, image quality, and
focus over a wide temperature range using thin lenses formed in the
coupling fluid between lens multiplets. Tight specifications for image quality and gravity-induced image motion and defocus lead to tight specifications for displacements of Binospec's optical elements. We describe how Binospec's elastomeric lens mounts have been tuned to attain this level of performance.
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