The Gemini Infrared Multi-Object Spectrograph (GIRMOS) is a new facility instrument being designed in close partnership with the upcoming facility adaptive optics (AO) system at Gemini-North observatory called GNAO. GIRMOS will carry out high angular resolution (0.83 – 2.4 µm) imaging and multi-object integral field (0.95 – 2.35 µm) spectroscopy within GNAO’s two arcminute field-of-regard. GIRMOS consists of an imager and four identical deployable integral field spectrographs with a multi-object AO system that provides an additional image quality improvement for each spectrograph over GNAO across the full field. We present the final design overview of GIRMOS, which will be entering the construction phase in 2024 with an expected delivery in 2027. GIRMOS is a pathfinder for future extremely large telescope instrumentation that requires high angular resolution, highly multiplexed spectroscopy.
In this paper we discuss the final mechanical design of the GIRMOS Cryostat. GIRMOS is an adaptive optics fed multi-object Integral-Field Spectrograph (IFS) with a parallel imaging capability and will be installed at the Gemini North Observatory. This instrument includes four identical spectrograph channels arranged symmetrically around a central optical axis which provides it with a multiplexing capability. GIRMOS has an object selection sub-assembly (OSEL) located upstream of the spectrographs which contains four motorized fold mirror assemblies that can scan the incoming light from the telescope to look at four separate sections of the sky simultaneously or can combine their efforts to look at a single larger section of the sky in a tiled mode. Each of the four individual IFS beams from the OSEL assembly is directed into the instrument Cryostat via its dedicated optical entrance window. Within the Cryostat each IFS beam moves through an anamorphic relay, an optical image slicer assembly, and eventually makes it to a spectrograph unit. In this paper, we will provide some details regarding the vacuum chamber design that houses the spectrographs, the design of the internal support structure, the opto-mechanical packaging of the IFS along with some of the thermal load mitigation techniques employed.
The Gemini Infrared Multi-Object Spectrograph (GIRMOS) will bring high-resolution integral-field spectroscopic and imaging capability to the Gemini North observatory. Designed to work with the Gemini North Adaptive Optics system, it has a multi-object adaptive optics capability that will provide increased resolution and sensitivity for the selected targets. The GIRMOS Calibration System (CAL) is an integral part of the GIRMOS instrument, providing photometric, spectroscopic and metrology calibration. A recent addition to GIRMOS is a field lens assembly (FLA), mechanically integrated with CAL, that provides a telecentric beam and optical shutter. This paper summarizes the final design, mechanical analysis, and optical tolerance analysis of the CAL/FLA subsystem.
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