MAVIS will be part of the next generation of VLT instrumentation and it will include a visible imager and a spectrograph, both fed by a common Adaptive Optics Module. The AOM consists in a MCAO system, whose challenge is to provide a 30” AO-corrected FoV in the visible domain, with good performance in a 50% sky coverage at the Galactic Pole. To reach the required performance, the current AOM scheme includes the use of up to 11 reference sources at the same time (8 LGSs + 3 NGSs) to drive more than 5000 actuators, divided into 3 deformable mirrors (one of them being UT4 secondary mirror). The system also includes some auxiliary loops, that are meant to compensate for internal instabilities (including WFSs focus signal, LGS tip-tilt signal and pupil position) so to push the stability of the main AO loop and the overall performance. Here we present the Preliminary Design of the AOM, which evolved, since the previous phase, as the result of further trade-offs and optimizations. We also introduce the main calibration strategy for the loops and sub-systems, including NCPA calibration approach. Finally, we present a summary of the main results of the performance and stability analyses performed for the current design phase, in order to show compliance to the performance requirements.
MAVIS is the world’s first facility-grade visible MCAO instrument, currently under development for the VLT. The AO system will feed an imager and an integral field spectrograph, with 50% sky coverage at the Galactic pole. MAVIS has unique angular resolution and sensitivity at visible wavelengths, and is highly complementary to both JWST and ELTs. We describe both instruments in detail and the broad range of science cases enabled by them. The imager will be diffraction-limited in V, with 7.36 mas per pixel covering a 30” FOV. A set of at least 7 broad-band and 15 narrow-band filters will provide imaging from u to z. The spectrograph uses an advanced image slicer with a selectable spatial sampling of 25 or 50 mas to provide integral field spectroscopy over a FOV of 2.5”x3.6”, or 5”x7.2”. The spectrograph has two identical arms each covering half the FOV. Four interchangeable grisms allow spectroscopy with R=5,000 to R=15,000, from 380-950 nm.
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