9 August 2016 An ultra-stable cryostat for the detectors of ESPRESSO
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Abstract
ESPRESSO The Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, is a super-stable Optical High Resolution Spectrograph for the combined coude focus of the VLT. It can be operated by either one of the UTs or collecting the light from up to 4 UTs simultaneously. Given the wide spectral range, the optical path is split into two channels, two large 90 mm x 90 mm CCDs are used to record the full spectrum. In order to achieve the extremely high stability, ESPRESSO has a fixed optical layout; no moving parts are foreseen inside the spectrograph to maximize the stability and repeatability of the instrument performance and to avoid any thermal load generated inside the spectrograph itself. The optical bench is placed in a vacuum vessel hosted in a three level enclosure system able to guarantee temperature stability of the order of 0.001 K and in a vacuum environment. We aim for a stability of the spectral line on the detector pixel matrix in the range of a few nanometers. The paper gives a detailed description of the cryostat with the flexible de-coupling of the Dewar between the vacuum vessel and optical bench. The design including the measures taken in order to provide an optimal thermal connection and a very accurate mechanical referencing of the large chip. We are going to describe the specific experiment which has been set-up in order to verify and physically measure the real stability of the detector “pixels” relative to the rest of the world. We will also present the results obtained with the similar setup measuring the stability of the HARPS detector (the precursor of ESPRESSO) and the preliminary results of the stability of the final ESPRESSO detector system.
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Jean Louis Lizon, Jean Louis Lizon, Olaf Iwert, Olaf Iwert, Sebastian Deiries, Sebastian Deiries, Hans Decker, Hans Decker, Renate Hinterschuster, Renate Hinterschuster, Antonio Manescau, Antonio Manescau, Denis Megevand, Denis Megevand, Eric Mueller, Eric Mueller, Francesco Alfonso Pepe, Francesco Alfonso Pepe, Marco Riva, Marco Riva, } "An ultra-stable cryostat for the detectors of ESPRESSO", Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 990866 (9 August 2016); doi: 10.1117/12.2231623; https://doi.org/10.1117/12.2231623
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