T. Buey

Experience with wavefront sensor and deformable mirror interfaces for wide-field adaptive optics systems

Recent advances in adaptive optics (AO) have led to the implementation of wide field-of-view AO systems. A number of wide-field AO systems are also planned for the forthcoming Extremely Large Telescopes. Such systems have multiple wavefront sensors of different types, and usually multiple deformable mirrors (DMs). Here, we report on our experience integrating cameras and DMs with the real-time control systems of two wide-field AO systems. These are CANARY, which has been operating on-sky since 2010, and DRAGON, which is a laboratory AO real-time demonstrator instrument. We detail the issues and difficulties that arose, along with the solutions we developed. We also provide recommendations for consideration when developing future wide-field AO systems.

The SPHERE XAO system: design and performance

Extreme adaptive optics system (SAXO) is the heart of the SPHERE instrument which aims at directly detect and characterize giant extra-solar planets from the ground. It should equip one of the four VLT 8-m telescopes at the end of 2010. We present a detailed design and architecture of the SAXO system. We focus on each critical point that has been solved during the preliminary design phase. It concerns the adaptive optics system itself but also the interaction with other SPHERE subsystems (such as coronagraphy) and focal plane instrumentation (dual band imager, integral field spectroscopy and polarimetric imager). Acceptance and integration tests of SAXO are discussed. Finally, detailed performance of the whole system and comparison to the science requirements are provided.

Persee: a nulling demonstrator with real-time correction of external disturbances

Nulling interferometry is one of the most promising methods to study habitable extrasolar systems. Several projects, such as Darwin, TPF, Pegase, FKSI or Aladdin, are currently considered and supported by R&D programs. One of the main issues of nulling interferometry is the feasibility of a stable polychromatic null despite the presence of significant disturbances, induced by vibrations, atmospheric turbulence on the ground or satellite drift for spaceborne missions. To reduce cost and complexity of the whole system, it is necessary to optimize not only the control loop performance at platform and payload levels, but also their interaction. In this goal, it was decided in 2006 to build a laboratory demonstrator named Persee. Persee is mostly funded by CNES and built by a consortium including CNES, IAS, LESIA, OCA, ONERA and TAS. After a definition phase in 2006, the implementation of the sub-systems has now begun and the integration near Paris by GIS-PHASE (LESIA, ONERA and GEPI) is planned in 2009. This paper details the main objectives of PERSEE, describes the definition of the bench, presents the current status and reports results obtained with the first sub-systems.

SAXO, the eXtreme Adaptive Optics System of SPHERE. Overview and calibration procedure

The direct imaging of exoplanet is a challenging goal of todays astronomy. The light transmitted by exoplanet atmosphere is of a great interest as it may witness for life sign. SPHERE is a second generation instrument for the VLT, dedicated to exoplanet imaging, detection, and characterisation. SPHERE is a global project of an European consortium of 11 institutes from 5 countries. We present here the state of the art of the AIT of the Adaptive Optics part of the instrument. In addition we present fine calibration procedures dedicated to eXtreme Adaptive Optics systems. First we emphasized on vibration and turbulence identification for optimization of the control law. Then, we describe a procedure able to measure and compensate for NCPA with a coronagraphic system.

The SPHERE XAO system SAXO: integration, test, and laboratory performance

Direct detection and spectral characterization of extra-solar planets is one of the most exciting and challenging areas in modern astronomy due to the very large contrast between the host star and the planet at very small angular separations. SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research in Europe) is a second-generation instrument for the ESO VLT dedicated to this scientific objective. It combines an extreme adaptive optics system, various coronagraphic devices and a suite of focal instruments providing imaging, integral field spectroscopy and polarimetry capabilities in the visible and near-infrared spectral ranges. The extreme Adaptive Optics (AO) system, SAXO, is the heart of the SPHERE system, providing to the scientific instruments a flat wavefront corrected from all the atmospheric turbulence and internal defects. We present an updated analysis of SAXO assembly, integration and performance. This integration has been defined in a two step process. While first step is now over and second one is ongoing, we propose a global overview of integration results. The main requirements and system characteristics are briefly recalled, then each sub system is presented and characterized. Finally the full AO loop first performance is assessed. First results demonstrate that SAXO shall meet its challenging requirements.

Current results of the PERSEE testbench: the cophasing control and the polychromatic null rate

Stabilizing a nulling interferometer at a nanometric level is the key issue to obtain deep null depths. The PERSEE breadboard has been designed to study and optimize the operation of cophased nulling bench in the most realistic disturbing environment of a space mission. This presentation focuses on the current results of the PERSEE bench. In terms of metrology, we cophased at 0.33 nm rms for the piston and 60 mas rms for the tip/tilt. A Linear Quadratic Gaussian (LQG) control coupled with an unsupervised vibration identification allows us to maintain that level of correction, even with characteristic vibrations of nulling interferometry space missions. These performances, with an accurate design and alignment of the bench, currently lead to a polychromatic unpolarised null depth of 8.9 × 10-6 stabilized at 2.7 × 10-7 on the [1.65 - 2.45] μm spectral band (37% bandwidth). With those significant results, we give the first more general lessons we have already learned from this experiment, both at system and component levels for a future space mission.

On‐sky demonstration of matched filters for wavefront measurements using ELT‐scale elongated laser guide stars

The performance of adaptive optics systems is partially dependent on the algorithms used within the real‐time control system to compute wavefront slope measurements. We demonstrate the use of a matched filter algorithm for the processing of elongated laser guide star (LGS) Shack‐Hartmann images, using the CANARY adaptive optics instrument on the 4.2 m William Herschel Telescope and the European Southern Observatory Wendelstein LGS Unit placed 40 m away. This algorithm has been selected for use with the forthcoming Thirty Meter Telescope, but until now had not been demonstrated on‐sky. From the results of a first observing run, we show that the use of matched filtering improves our adaptive optics system performance, with increases in on‐sky H‐band Strehl measured up to about a factor of 1.1 with respect to a conventional centre of gravity approach. We describe the algorithm used, and the methods that we implemented to enable on‐sky demonstration.

PERSEE: experimental results on the cophased nulling bench

Nulling interferometry is still a promising method to characterize spectra of exoplanets. One of the main issues is to cophase at a nanometric level each arm despite satellite disturbances. The bench PERSEE aims to prove the feasibility of that technique for spaceborne missions. After a short description of PERSEE, we will first present the results obtained in a simplified configuration: we have cophased down to 0.22 nm rms in optical path difference (OPD) and 60 mas rms in tip/tilt, and have obtained a monochromatic null of 3 · 10-5 stabilized at 3•10-6. The goal of 1 nm with additional typical satellite disturbances requires the use of an optimal control law; that is why we elaborated a dedicated Kalman filter. Simulations and experiments show a good rejection of disturbances. Performance of the bench should be enhanced by using a Kalman control law, and we should be able to reach the desired nanometric stability. Following, we will present the first results of the final polychromatic configuration, which includes an achromatic phase shifter, perturbators and optical delay lines. As a conclusion, we give the first more general lessons we have already learned from this experiment, both at system and component levels for a future space mission.

First scattered light detection of a nearly edge-on transition disk around the T Tauri star RY Lupi

Context. Transition disks are considered sites of ongoing planet formation, and their dust and gas distributions could be signposts of embedded planets. The transition disk around the T Tauri star RY Lup has an inner dust cavity and displays a strong silicate emission feature. Aims. Using high-resolution imaging we study the disk geometry, including non-axisymmetric features, and its surface dust grain, to gain a better understanding of the disk evolutionary process. Moreover, we search for companion candidates, possibly connected to the disk. Methods. We obtained high-contrast and high angular resolution data in the near-infrared with the VLT/SPHERE extreme adaptive optics instrument whose goal is to study the planet formation by detecting and characterizing these planets and their formation environments through direct imaging. We performed polarimetric imaging of the RY Lup disk with IRDIS (at 1.6 μm), and obtained intensity images with the IRDIS dual-band imaging camera simultaneously with the IFS spectro-imager (0.9–1.3 μm). Results. We resolved for the first time the scattered light from the nearly edge-on circumstellar disk around RY Lup, at projected separations in the 100 au range. The shape of the disk and its sharp features are clearly detectable at wavelengths ranging from 0.9 to 1.6 μm. We show that the observed morphology can be interpreted as spiral arms in the disk. This interpretation is supported by in-depth numerical simulations. We also demonstrate that these features can be produced by one planet interacting with the disk. We also detect several point sources which are classified as probable background objects.

An aperture masking mode for the MICADO instrument

MICADO is a near-IR camera for the European ELT, featuring an extended field (75” diameter) for imaging, and also spectrographic and high contrast imaging capabilities. It has been chosen by ESO as one of the two first-light instruments. Although it is ultimately aimed at being fed by the MCAO module called MAORY, MICADO will come with an internal SCAO system that will be complementary to it and will deliver a high performance on axis correction, suitable for coronagraphic and pupil masking applications. The basis of the pupil masking approach is to ensure the stability of the optical transfer function, even in the case of residual errors after AO correction (due to non common path errors and quasi-static aberrations). Preliminary designs of pupil masks are presented. Trade-offs and technical choices, especially regarding redundancy and pupil tracking, are explained.