Reconstruction of the ground-layer adaptive-optics point spread function for MUSE wide field mode observations

T Fusco,S Conseil,P.-Y Madec,B Neichel,R Bacon,J Vernet,O Beltramo-Martin,C Correia,S Kamann,J Kolb

doi:10.1051/0004-6361/202037595

Abstract

Context. Here we describe a simple, efficient, and most importantly fully operational point-spread-function (PSF)-reconstruction approach for laser-assisted ground layer adaptive optics (GLAO) in the frame of the Multi Unit Spectroscopic Explorer (MUSE) wide field mode. Aims. Based on clear astrophysical requirements derived by the MUSE team and using the functionality of the current ESO Adaptive Optics Facility we aim to develop an operational PSF-reconstruction (PSFR) algorithm and test it both in simulations and using on-sky data. Methods. The PSFR approach is based on a Fourier description of the GLAO correction to which the specific instrumental effects of MUSE wide field mode (pixel size, internal aberrations, etc.) have been added. It was first thoroughly validated with full end-to-end simulations. Sensitivity to the main atmospheric and AO system parameters was analysed and the code was re-optimised to account for the sensitivity found. Finally, the optimised algorithm was tested and commissioned using more than one year of on-sky MUSE data. Results. We demonstrate with an on-sky data analysis that our algorithm meets all the requirements imposed by the MUSE scientists, namely an accuracy better than a few percent on the critical PSF parameters including full width at half maximum and global PSF shape through the kurtosis parameter of a Moffat function. Conclusions. The PSFR algorithm is publicly available and is used routinely to assess the MUSE image quality for each observation. It can be included in any post-processing activity which requires knowledge of the PSF.

Highlights

Achieved image quality is usually the primary parameter of successful observations, especially those performed at groundbased telescopes where atmospheric turbulence produces highly changeable conditions
In order to obtain more quantitative results, we propose in the following to compute an error metric between the final computed parameters using the full PSFR process and the measured parameters obtained on the Globular Cluster images: errp = pmeasured − ppredicted
Efficient, and fully operational point spread function (PSF)-reconstruction algorithm based on a Fourier analysis of the ground layer adaptive optics (GLAO) residual phase statistics completed by dedicated information and measurements concerning the instrument itself

Summary

Introduction

Achieved image quality is usually the primary parameter of successful observations, especially those performed at groundbased telescopes where atmospheric turbulence produces highly changeable conditions. An obvious example is the comparison with higher spatial resolution space observations, like those obtained with the Hubble Space Telescope, which achieve a ten times higher resolution than classical ground-based observations in median seeing conditions. The PSF full width at half maximum (FWHM) is often used to quantify the achieved image quality. Most modern ground-based telescopes are equipped with a seeing monitor which provides a real-time estimate of the FWHM. This is very convenient to get a rough estimate of the PSF, but it is usually not accurate enough in a number of science applications. The measurement is taken with a small telescope and does not take into account the relative outer-scale size of the turbulence with respect to the size of the telescope, or the image quality of the telescope plus instrument system

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Conclusion