In-flight performance and calibration of the Grating Wheel Assembly sensors (NIRSpec/JWST)

Catarina Alves de Oliveira; Nora Luetzgendorf; Peter Zeidler; Giovanna Giardino; Pierre Ferruit; Nimisha Kumari; Timothy Rawle; Stephan M. Birkmann; Torsten Boeker; Charles Proffitt; Marco Sirianni; Maurice Te Plate

arXiv · 2208.05354

In-flight performance and calibration of the Grating Wheel Assembly sensors (NIRSpec/JWST)

Catarina Alves de Oliveira·Nora Luetzgendorf·Peter Zeidler·Giovanna Giardino·Pierre Ferruit·Nimisha Kumari·Timothy Rawle·Stephan M. Birkmann·Torsten Boeker·Charles Proffitt·Marco Sirianni·Maurice Te Plate

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Abstract

The Near-Infrared Spectrograph (NIRSpec) on board of the James Webb Space Telescope will be the first multi-object spectrograph in space offering ~250,000 configurable micro-shutters, apart from being equipped with an integral field unit and fixed slits. At its heart, the NIRSpec grating wheel assembly is a cryogenic mechanism equipped with six dispersion gratings, a prism, and a mirror. The finite angular positioning repeatability of the wheel causes small but measurable displacements of the light beam on the focal plane, precluding a static solution to predict the light-path. To address that, two magneto-resistive position sensors are used to measure the tip and tilt displacement of the selected GWA element each time the wheel is rotated. The calibration of these sensors is a crucial component of the model-based approach used for NIRSpec for calibration, spectral extraction, and target placement in the micro-shutters. In this paper, we present the results of the evolution of the GWA sensors performance and calibration from ground to space environments.

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Catarina Alves de Oliveira, Nora Luetzgendorf, Peter Zeidler, Giovanna Giardino, Pierre Ferruit, Nimisha Kumari, Timothy Rawle, Stephan M. Birkmann, Torsten Boeker, Charles Proffitt, Marco Sirianni, Maurice Te Plate. 2022-08-10. In-flight performance and calibration of the Grating Wheel Assembly sensors (NIRSpec/JWST). https://arxiv.org/abs/2208.05354

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