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

Abstract

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 at...

First direct detection of a polarized companion outside a resolved circumbinary disk around CS Chamaeleonis

“…This was used to produce a 2D attenuation profile of the coronagraph for an extended, incoherent source. Monochromatic Fourier modeling of the threeplane APLC coronagraph was also performed, using the APO1 SPHERE amplitude apodiser, ACL2 (185 mas diameter) focalplane mask and NIR Lyot stop including dead actuator masks (Guerri et al 2011, Sauvage et al 2016. This model confirmed that the observed Ceres attenuation profile is nearly diffractionlimited and azimuthally symmetric.…”

Optical polarised phase function of the HR 4796A dust ring

“…The star HR 4796 A was observed on the night of 24 May, 2016, with the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE Beuzit et al 2019). SPHERE is a high-contrast imager fed by an extreme adaptive optics (AO) system (Sauvage et al 2016b) to correct for the atmospheric turbulence and static aberrations. These observations were part of the Guaranteed Time Observations of the SPHERE consortium 1 and made use of the visible subsystem Zurich IMaging POLarimeter (ZIMPOL, Schmid et al 2018) to observe the star in linear polarized light.…”

SPHERE: the exoplanet imager for the Very Large Telescope

“…It is used to measure and correct any incoming wavefront perturbation (rapidly varying turbulence or quasi-static instrumental speckles) to ensure a high image quality. The system is fully specified in Fusco et al (2006) and all the laboratory validations and performance are detailed in Sauvage et al (2016b) and Petit et al (2012). The results presented in this section correspond to the SAXO configuration validated during SPHERE commissioning and science verification periods.…”