Characterizing vibrations at the Subaru Telescope for the Subaru coronagraphic extreme adaptive optics instrument

Julien Lozi; Olivier Guyon; Nemanja Jovanovic; Naruhisa Takato; Garima Singh; Barnaby Norris; Hirofumi Okita; Takamasa Bando; Frantz Martinache

doi:10.1117/1.JATIS.4.4.049001

12 September 2018 Characterizing vibrations at the Subaru Telescope for the Subaru coronagraphic extreme adaptive optics instrument

Julien Lozi, Olivier Guyon, Nemanja Jovanovic, Naruhisa Takato, Garima Singh, Barnaby Norris, Hirofumi Okita, Takamasa Bando, Frantz Martinache

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Journal of Astronomical Telescopes, Instruments, and Systems, Vol. 4, Issue 4, 049001 (September 2018). https://doi.org/10.1117/1.JATIS.4.4.049001

Abstract

Vibrations are a key source of image degradation in ground-based instrumentation, especially for high-contrast imaging instruments. Vibrations reduce the quality of the correction provided by the adaptive optics system, blurring the science image, and reducing the sensitivity of most science modules. We studied vibrations using the Subaru coronagraphic extreme adaptive optics instrument at the Subaru Telescope as it is the most vibration-sensitive system installed on the telescope. We observed vibrations for all targets, usually at low frequency, below 10 Hz. Using accelerometers on the telescope, we confirmed that these vibrations were introduced by the telescope itself, and not the instrument. It was determined that they were related to the pitch of the encoders of the telescope drive system, both in altitude and azimuth, with frequencies evolving proportionally to the rotational speed of the telescope. Another strong vibration was found in the altitude axis of the telescope, around the time of transit of the target, when the altitude rotational speed is below 0.12 arc sec / s. These vibrations are amplified by the 10-Hz control loop of the telescope, especially in a region between 4 and 6 Hz. We demonstrate an accurate characterization of the frequencies of the telescope vibrations using only the coordinates—right ascension and declination—of the target and provide a means by which we can predict them for any telescope pointing. This will be a powerful tool that can be used by more advanced wavefront control algorithms, especially predictive control that uses information about the disturbance to calculate the best correction.

CC BY: © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Julien Lozi, Olivier Guyon, Nemanja Jovanovic, Naruhisa Takato, Garima Singh, Barnaby Norris, Hirofumi Okita, Takamasa Bando, and Frantz Martinache "Characterizing vibrations at the Subaru Telescope for the Subaru coronagraphic extreme adaptive optics instrument," Journal of Astronomical Telescopes, Instruments, and Systems 4(4), 049001 (12 September 2018). https://doi.org/10.1117/1.JATIS.4.4.049001

Received: 6 April 2018; Accepted: 16 August 2018; Published: 12 September 2018

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