PLC-controlled cryostats for the BlackGEM and MeerLICHT detectors

BlackGEM is an array of telescopes, currently under development at the Radboud University Nijmegen and at NOVA (Netherlands Research School for Astronomy). It targets the detection of the optical counterparts of gravitational waves. The first three BlackGEM telescopes are planned to be installed in 2018 at the La Silla observatory (Chile). A single prototype telescope, named MeerLICHT, will already be commissioned early 2017 in Sutherland (South Africa) to provide an optical complement for the MeerKAT radio array. The BlackGEM array consists of, initially, a set of three robotic 65-cm wide-field telescopes. Each telescope is equipped with a single STA1600 CCD detector with 10.5k x 10.5k 9-micron pixels that covers a 2.7 square degrees field of view. The cryostats for housing these detectors are developed and built at the KU Leuven University (Belgium). The operational model of BlackGEM requires long periods of reliable hands-off operation. Therefore, we designed the cryostats for long vacuum hold time and we make use of a closed-cycle cooling system, based on Polycold PCC Joule-Thomson coolers. A single programmable logic controller (PLC) controls the cryogenic systems of several BlackGEM telescopes simultaneously, resulting in a highly reliable, cost-efficient and maintenance-friendly system. PLC-based cryostat control offers some distinct advantages, especially for a robotic facility. Apart of temperature monitoring and control, the PLC also monitors the vacuum quality, the power supply and the status of the PCC coolers (compressor power consumption and temperature, pressure in the gas lines, etc.). Furthermore, it provides an alarming system and safe and reproducible procedures for automatic cool down and warm up. The communication between PLC and higher-level software takes place via the OPC-UA protocol, offering a simple to implement, yet very powerful interface. Finally, a touch-panel display on the PLC provides the operator with a user-friendly and robust technical interface. In this contribution, we present the design of the BlackGEM cryostats and of the PLC-based control system.11 pages, SPIE Astronomical Telescopes and Instrumentation 2016 Conference Proceedingsstatus: publishe

Calibrating SPHERE, the exo-planet imager for the VLT

International audienceOne of the main challenges to obtain the contrast of >15mag targeted by an extra-solar planet imager like SPHERE lies in the calibration of all the different elements participating in the final performance. Starting with the calibration of the AO system and its three embedded loops, the calibration of the non-common path aberrations, the calibration of the NIR dual band imager, the NIR integral field spectrograph, the NIR spectrograph, the visible high accuracy polarimeter and the visible imager all require sophisticated calibration procedures. The calibration process requires a specific extensive calibration unit that provides the different sources across the spectrum (500-2320nm) with the stabilities and precisions required. This article addresses the challenges met by the hardware and the instrument software used for the calibration of SPHERE

SAXO: the extreme adaptive optics system of SPHERE (I) system overview and global laboratory performance

International audienceThe direct imaging of exoplanet is a leading field of today’s astronomy. The photons coming from the planet carry precious information on the chemical composition of its atmosphere. The second-generation instrument, Spectro-Polarimetric High contrast Exoplanet Research (SPHERE), dedicated to detection, photometry and spectral characterization of Jovian-like planets, is now in operation on the European very large telescope. This instrument relies on an extreme adaptive optics (XAO) system to compensate for atmospheric turbulence as well as for internal errors with an unprecedented accuracy. We demonstrate the high level of performance reached by the SPHERE XAO system (SAXO) during the assembly integration and test (AIT) period. In order to fully characterize the instrument quality, two AIT periods have been mandatory. In the first phase at Observatoire de Paris, the performance of SAXO itself was assessed. In the second phase at IPAG Grenoble Observatory, the operation of SAXO in interaction with the overall instrument has been optimized. In addition to the first two phases, a final check has been performed after the reintegration of the instrument at Paranal Observatory, in the New Integration Hall before integration at the telescope focus. The final performance aimed by the SPHERE instrument with the help of SAXO is among the highest Strehl ratio pretended for an operational instrument (90% in H band, 43% in V band in a realistic turbulence r0, and wind speed condition), a limit R magnitude for loop closure at 15, and a robustness to high wind speeds. The full-width at half-maximum reached by the instrument is 40 mas for infrared in H band and unprecedented 18.5 mas in V band.L'imagerie directe d'exoplanètes est un domaine phare de l'astronomie actuelle. Les photons issus de la planète sont porteurs d'une information précieuse sur la composition chimique de son atmosphère. L'instrument de seconde génération SPHERE, Spectro-Polarimetri High-contrast Exoplanet Research, dédié à la détection la photométrie et la caractérisation spectrale de planètes joviennes, est maintenant en opération sur le très grand télescope Européen (VLT). Cet instrument repose sur une optique adaptative à très hautes performances (XAO) pour compenser les turbulences atmosphériques, comme les défauts optiques internes de l'instrument lui-même. Nous démontrons les très hauts niveaux de performance atteint par l'instrument SPHERE et son système de XAO SAXO, pendant la phase d'intégration (AIT). Pour pleinement caractériser les performances de l'instrument, deux périodes d'AIT ont été obligatoires. Dans la première phase à l'Observatoire de Paris, les performances de l'optique adaptative seule ont été obtenues. Dans la seconde phase à l'observatoire de Grenoble, l'opération de SAXO en interaction avec le reste de l'instrument ont été optimisées. En sus, une vérification finale a été faite au foyer du télescope. Les performances atteintes par SPHERE avec l'aide de SAXO sont parmi les plus hauts rapports de Strehl jamais atteint pour un instrument opérationnel (90% en bande H, 43% en bande V, sous hypothèse de turbulence et de vent classiques), et surtout une magnitude limite de R=15. La FHWM (largeur à mi-hauteur, la résolution de l'instrument) atteinte en bande H est de 40mas, et atteint une valeur sans précédent de 18.5mas en bande V

SPHERE on-sky performance compared with budget predictions

International audienceThe SPHERE (spectro-photometric exoplanet research) extreme-AO planet hunter saw first light at the VLT observatory on Mount Paranal in May 2014 after ten years of development. Great efforts were put into modelling its performance, particularly in terms of achievable contrast, and to budgeting instrumental features such as wave front errors and optical transmission to each of the instrument's three focal planes, the near infrared dual imaging camera IRDIS, the near infrared integral field spectrograph IFS and the visible polarimetric camera ZIMPOL. In this paper we aim at comparing predicted performance with measured performance. In addition to comparing on-sky contrast curves and calibrated transmission measurements, we also compare the PSD-based wave front error budget with in-situ wave front maps obtained thanks to a Zernike phase mask, ZELDA, implemented in the infrared coronagraph wheel. One of the most critical elements of the SPHERE system is its high-order deformable mirror, a prototype 40x40 actuator piezo stack design developed in parallel with the instrument itself. The development was a success, as witnessed by the instrument performance, in spite of some bad surprises discovered on the way. The devastating effects of operating without taking properly into account the loss of several actuators and the thermally and temporally induced variations in the DM shape will be analysed, and the actions taken to mitigate these defects through the introduction of specially designed Lyot stops and activation of one of the mirrors in the optical train will be described

The HIP 79977 debris disk in polarized light

ISSN:0004-6361ISSN:1432-074

3MeerLICHT and BlackGEM: custom-built telescopes to detect faint optical transients

We present the MeerLICHT and BlackGEM telescopes, which are wide-field optical telescopes that are currently being built to study transient phenomena, gravitational wave counterparts and variable stars. The telescopes have 65 cm primary mirrors and a 2.7 square degree field-of-view. The MeerLICHT and BlackGEM projects have different science goals, but will use identical telescopes. The first telescope, MeerLICHT, will be commissioned at Sutherland (South Africa) in the first quarter of 2017. It will co-point with MeerKAT to collect optical data commensurate with the radio observations. After careful analysis of MeerLICHT's performance, three telescopes of the same type will be commissioned in La Silla (Chile) in 2018 to form phase I of the BlackGEM array. BlackGEM aims at detecting and characterizing optical counterparts of gravitational wave events detected by Advanced LIGO and Virgo. In this contribution we present an overview of the science goals, the design and the status of the two projects