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Proceedings Paper

PSF modeling by spikes simulations and wings measurements for the MOONS multi fiber spectrograph
Author(s): G. Li Causi; D. Lee; F. Vitali; F. Royer; E. Oliva
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Paper Abstract

The optical design of MOONS, the next generation thousand-fiber NIR spectrograph for the VLT, involves both on-axis reflective collimators and on-axis very fast reflective cameras, which yields both beam obstruction, due to fiber slit and detector support, and image spread, due to propagation within detector substrate. The need to model and control i) the effect of the diffraction spikes produced by these obstructions, ii) the detector-induced shape variation of the Point Spread Function (PSF), and iii) the intensity profile of the PSF wings, leads us to perform both simulations and lab measurements, in order to optimize the spider design and built a reliable PSF model, useful for simulate realistic raw images for testing the data reduction. Starting from the unobstructed PSF variation, as computed with the ZEMAX software, we numerically computed the diffraction spikes for different spider shapes, to which we added the PSF wing profile, as measured on a sample of the MOONS VPH diffraction grating. Finally, we implemented the PSF defocusing due to the thick detector (for the visible channel), we convolved the PSF with the fiber core image, and we added the optical ghosts, so finally obtaining a detailed and realistic PSF model, that we use for spectral extraction testing, cross talk estimation, and sensitivity predictions.

Paper Details

Date Published: 9 August 2016
PDF: 13 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 99088P (9 August 2016); doi: 10.1117/12.2232964
Show Author Affiliations
G. Li Causi, INAF - Osservatorio Astronomico di Roma (Italy)
D. Lee, UK Astronomy Technology Ctr. (United Kingdom)
F. Vitali, INAF - Osservatorio Astronomico di Roma (Italy)
F. Royer, GEPI, Observatoire de Paris, PSL Research Univ., CNRS, Univ. Paris Diderot (France)
E. Oliva, INAF - Osservatorio Astrofisico di Arcetri (Italy)


Published in SPIE Proceedings Vol. 9908:
Ground-based and Airborne Instrumentation for Astronomy VI
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)

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