ELTs have the potential for imaging reflected light from habitable rocky planets around M-stars. To address that exciting science we present the PDR level optical-mechanical design for a high-contrast coronagraphic instrument for the 25.4m Giant Magellan Telescope (GMT) called GMagAO-X. It is a first light extreme adaptive optics (ExAO) coronagraphic instrument which mounts to the sector D folded port of the GMT. To meet the strict ExAO fitting and servo error requirement (<90nm rms WFE), GMagAO-X must have 21,000 actuator DM capable of >2KHz update speeds. To minimize wavefront/segment piston error GMagAO-X has an interferometric beam combiner on a vibration isolated table, as part of this 21,000 actuator “parallel DM”. Segment/petal piston errors are continuously sensed by a novel Holographic Dispersed Fringe Sensor (HDFS). In addition to a coronagraph, it has a post-coronagraphic Lyot Low Order WFS (LLOWFS) to sense non-common path (NCP) errors. The LLOWFS drives a non-common path DM (NCP DM) to correct those NCP errors. GMagAO-X obtains high-contrast science and wavefront sensing in the visible or the NIR. Here we present our successful, externally reviewed (Feb. 2024), PDR optical-mechanical design that satisfies GMagAO-X’s top-level science requirements and is compliant with the GMT instrument requirements/ICDs and only requires COTS parts and readily available 2-5 inch sized optics. We have also prototyped the parallel DM and the HDFS phasing sensor on the HCAT testbed. We show initial phased HCAT testbed results for the parallel DM and initial on-sky phasing results for HDFS.
We present the preliminary design of GMagAO-X, the first-light high-contrast imager planned for the Giant Magellan Telescope. GMagAO-X will realize the revolutionary increase in spatial resolution and sensitivity provided by the 25 m GMT. It will enable, for the first time, the spectroscopic characterization of nearby potentially habitable terrestrial exoplanets orbiting late-type stars. Additional science cases include: reflected light characterization of mature giant planets; measurement of young extrasolar giant planet variability; characterization of circumstellar disks at unprecedented spatial resolution; characterization of benchmark stellar atmospheres at high spectral resolution; and mapping of resolved objects such as giant stars and asteroids. These, and many more, science cases will be enabled by a 21,000 actuator extreme adaptive optics system, a coronagraphic wavefront control system, and a suite of imagers and spectrographs. We will review the science-driven performance requirements for GMagAO-X, which include achieving a Strehl ratio of 70% at 800 nm on 8th mag and brighter stars, and post-processed characterization at astrophysical flux-ratios of 1e-7 at 4 lambda/D (26 mas at 800 nm) separation. We will provide an overview of the resulting mechanical, optical, and software designs optimized to deliver this performance. We will also discuss the interfaces to the GMT itself, and the concept of operations. We will present an overview of our end-to-end performance modeling and simulations, including the control of segment phasing, as well as an overview of prototype lab demonstrations. Finally, we will review the results of Preliminary Design Review held in February, 2024.
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