The Multi Unit Spectroscopic Explorer (MUSE) is an integral field spectrograph on the Very Large Telescope Unit Telescope 4, capable of laser guide star assisted and tomographic adaptive optics using the GALACSI module. Its observing capabilities include a wide field (1 square arcmin), ground layer AO mode (WFM-AO) and a narrow field (7.5”×7.5”), laser tomography AO mode (NFM-AO). The latter has had several upgrades in the 4 years since commissioning, including an optimization of the control matrices for the AO system and a new sub-electron noise detector for its infra-red low order wavefront sensor. We set out to quantify the NFM-AO system performance by analysing ∼230 spectrophotometric standard star observations taken over the last 3 years. To this end we expand upon previous work, designed to facilitate analysis of the WFM-AO system performance. We briefly describe the framework that will provide a user friendly, semi-automated way for system performance monitoring during science operations. We provide the results of our performance analysis, chiefly through the measured Strehl ratio and full width at half maximum (FWHM) of the core of the point spread function (PSF) using two PSF models, and correlations with atmospheric conditions. These results will feed into a range of applications, including providing a more accurate prediction of the system performance as implemented in the exposure time calculator, and the associated optimization of the scientific output for a given set of limiting atmospheric conditions.
The Multi-Unit Spectroscopic Explorer instrument (MUSE), is an integral-field spectrograph at one of the Nasmyth foci of the 8m-class Yepun telescope at Paranal observatory. MUSE's most powerful modes use the Adaptive Optics Facility consisting of a Deformable Secondary Mirror with over 1000 actuators commanded by a real-time computer up to 1000 times per second. At the core of the system are 4 laser guide stars monitored by GALACSI, the wave-front sensor system. MUSE functions with two modes: Wide-Field Mode (1'x1' field), making use of Ground Layer Adaptive Optics and Narrow-Field Mode (7.5"x7.5" field) using full laser tomography. In this work, we will present the results of a campaign to monitor the AO performance as measured by MUSE during the first years of operations. We will evaluate the dependence of this performance, as characterized by the point-spread function, on easily monitored environmental parameters such as ground-layer fraction, coherence time, seeing, and airmass.
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