M. Kasper

Final performance and lesson-learned of SAXO, the VLT-SPHERE extreme AO: from early design to on-sky results

The extreme AO system, SAXO (SPHERE AO for eXoplanet Observation), is the heart of the SPHERE system, feeding the scientific instruments with flat wave front corrected from all the atmospheric turbulence and internal defects. We will present the final performance of SAXO obtained during the instrument AIT in Europe as well as the very first on-sky results. The main requirements and system characteristics will be recalled and the full AO loop performance will be quantified and compared to original specifications. It will be demonstrated that SAXO meets or even exceeds (especially its limit magnitude and its jitter residuals) its challenging requirements (more than 90% of SR in H band and a 3 mas residual jitter). Finally, after 10 years of AO developments, from early design to final on-sky implementations, some critical system aspects as well as some important lesson-learned will be presented in the perspective of the future generation of complex AO systems for VLTs and ELTs.

SPHERE eXtreme AO control scheme: final performance assessment and on sky validation of the first auto-tuned LQG based operational system

The SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument is an ESO project aiming at the direct detection of extra-solar planets. SPHERE has been successfully integrated and tested in Europe end 2013 and has been re-integrated at Paranal in Chile early 2014 for a first light at the beginning of May. The heart of the SPHERE instrument is its eXtreme Adaptive Optics (XAO) SAXO (SPHERE AO for eXoplanet Observation) subsystem that provides extremely high correction of turbulence and very accurate stabilization of images for coronagraphic purpose. However, SAXO, as well as the overall instrument, must also provide constant operability overnights, ensuring robustness and autonomy. An original control scheme has been developed to satisfy this challenging dichotomy. It includes in particular both an Optimized Modal Gain Integrator (OMGI) to control the Deformable Mirror (DM) and a Linear Quadratic Gaussian (LQG) control law to manage the tip-tilt (TT) mirror. LQG allows optimal estimation and prediction of turbulent angle of arrival but also of possible vibrations. A specific and unprecedented control scheme has been developed to continuously adapt and optimize LQG control ensuring a constant match to turbulence and vibrations characteristics. SPHERE is thus the first operational system implementing LQG, with automatic adjustment of its models. SAXO has demonstrated performance beyond expectations during tests in Europe, in spite of internal limitations. Very first results have been obtained on sky last May. We thus come back to SAXO control scheme, focusing in particular on the LQG based TT control and the various upgrades that have been made to enhance further the performance ensuring constant operability and robustness. We finally propose performance assessment based on in lab performance and first on sky results and discuss further possible improvements.

The ESO Adaptive Optics Facility

The Adaptive Optics Facility is a project to convert one VLT-UT into a specialized Adaptive Telescope. The present secondary mirror (M2) will be replaced by a new M2-Unit hosting a 1170 actuators deformable mirror. The 3 focal stations will be equipped with instruments adapted to the new capability of this UT. Two instruments are in development for the 2 Nasmyth foci: Hawk-I with its AO module GRAAL allowing a Ground Layer Adaptive Optics correction and MUSE with GALACSI for GLAO correction and Laser Tomography Adaptive Optics correction. A future instrument still needs to be defined for the Cassegrain focus. Several guide stars are required for the type of adaptive corrections needed and a four Laser Guide Star facility (4LGSF) is being developed in the scope of the AO Facility. Convex mirrors like the VLT M2 represent a major challenge for testing and a substantial effort is dedicated to this. ASSIST, is a test bench that will allow testing of the Deformable Secondary Mirror and both instruments with simulated turbulence. This article describes the Adaptive Optics facility systems composing associated with it.

Simulation of planet detection with the SPHERE integral field spectrograph

Aims. We present simulations of the perfomances of the future SPHERE IFS instrument designed for imaging extrasolar planets in the near infrared (Y, J, and H bands). Methods. We used the IDL package code for adaptive optics simulation (CAOS) to prepare a series of input point spread functions (PSF). These feed an IDL tool (CSP) that we designed to simulate the datacube resulting from the SPHERE IFS. We performed simulations under different conditions to evaluate the contrast that IFS will be able to reach and to verify the impact of physical propagation within the limits of the near field of the aperture approximation (i.e. Fresnel propagation). We then performed a series of simulations containing planet images to test the capability of our instrument to correctly classify the found objects. To this purpose we developed a separated IDL tool. Results. We found that using the SPHERE IFS instrument and appropriate analysis techniques, such as multiple spectral differential imaging (MDI), spectral deconvolution (SD), and angular differential imaging (ADI), we should be able to image companion objects down to a luminosity contrast of similar to 10(-7) with respect to the central star in favorable cases. Spectral deconvolution resulted in the most effective method for reducing the speckle noise. We were then able to find most of the simulated planets (more than 90% with the Y-J-mode and more than the 95% with the Y-H-mode) for contrasts down to 3 x 10(-7) and separations between 0.3 and 1.0 arcsec. The spectral classification is accurate but seems to be more precise for late T-type spectra than for earlier spectral types. A possible degeneracy between early L-type companion objects and field objects (flat spectra) is highlighted. The spectral classification seems to work better using the Y-H-mode than with the Y-J-mode.Aims. We presentsimulations of the perfomances of the future SPHERE IFS instrument desig n d for imaging extrasolar planets in the near infrared (Y, J, and H bands). Methods. We used the IDL package code for adaptive optics simulation ( CAOS) to prepare a series of input point spread functions (PSF). These feed an IDL tool (CSP) that we designed to simula te the datacube resulting from the SPHERE IFS. We performed simulations under di fferent conditions to evaluate the contrast that IFS will be ab l to reach and to verify the impact of physical propagation within the limits of the near field of the apertur e approximation (i.e. Fresnel propagation). We then perfor med a series of simulations containing planet images to test the capabilit y of our instrument to correctly classify the found objects. To this purpose we developed a separated IDL tool. Results. We found that using the SPHERE IFS instrument and appropriat e analysis techniques, such as multiple spectral di fferential imaging (MDI), spectral deconvolution (SD), and angular di fferential imaging (ADI), we should be able to image companion objects down to a luminosity contrast of ∼ 10−7 with respect to the central star in favorable cases. Spectra l deconvolution resulted in the most effective method for reducing the speckle noise. We were then ab le to find most of the simulated planets (more than 90% with the Y-J-mode and more than the 95% with the Y-H-mode) for contras ts down to 3× 10−7 and separations between 0.3 and 1.0 arcsec. The spectral classification is accurate but seems to be more p recise for late T-type spectra than for earlier spectral typ es. A possible degeneracy between early L-type companion objects and field objects (flat spectra) is highlighted. The spectral classifi cation seems to work better using the Y-H-mode than with the Y-J-mode.

An overview of the E-ELT instrumentation programme

In this paper we present a brief status report on the conceptual designs of the instruments and adaptive optics modules that have been studied for the European Extremely Large Telescope (E-ELT). In parallel with the design study for the 42-m telescope, ESO launched 8 studies devoted to the proposed instruments and 2 for post-focal adaptive optics systems. The studies were carried out in consortia of ESO member state institutes or, in two cases, by ESO in collaboration with external institutes. All studies have now been successfully completed. The result is a powerful set of facility instruments which promise to deliver the scientific goals of the telescope. The aims of the individual studies were broad: to explore the scientific capabilities required to meet the E-ELT science goals, to examine the technical feasibility of the instrument, to understand the requirements placed on the telescope design and to develop a delivery plan. From the perspective of the observatory, these are key inputs to the development of the proposal for the first generation E-ELT instrument suite along with the highest priority science goals and budgetary and technical constraints. We discuss the lessons learned and some of the key results of the process.

Optical Design and Test of the BIGRE Based IFS of SPHERE

During the last months IFS, is the Integral Field Spectrograph for SPHERE, devoted to the search of exoplanets has been integrated in the clean room of Padova Observatory. The design of IFS is based on a new concept of double microlens array sampling the focal plane. This device named BIGRE consists of a system made of two microlens arrays with different focal lengths and thickness equal to the sum of them and precisely aligned each other. Moreover a mask has been deposited on the first array to produce a field stop for each lenslet, and a second mask is located on the intermediate pupil of the IFS to provide an aperture stop. After characterization of a previous prototype of BIGRE in the visible range, now the first measurements of the performances of the device in the IR range have been obtained on the instrument that will be mounted at the VLT telescope. These tests confirmed that specifications and properties of the prototype are met by state of the art on optics microlens manufacturing.

The pyramid wavefront sensor for the high order testbench (HOT)

The High Order Testbench (HOT) is a joint experiment of ESO, Durham University and Arcetri Observatory to built and test in laboratory the performance of Shack-Hartmann and pyramid sensor in a high-order correction loop using a 32x32 actuators MEMS DM. This paper will describe the pyramid wavefront sensor unit developed in Arcetri and now installed in the HOT bench at ESO premises. In the first part of this paper we will describe the pyramid wavefront sensor opto-mechanics and its real-time computer realized with a commercial Linux-PC. In the second part we will show the sensor integration and alignment in the HOT bench and the experimental results obtained at ESO labs. Particular attention will be paid to the implementation of the modal control strategy, like modal basis definition, orthogonalization on the real pupil, and control of edge actuators. A stable closed loop controlling up to 667 modes has been achieved obtaining a Strehl ratio of 90 -- 93% in H band.

ELT instrument concepts: impact on telescope and adaptive optics design

We report on the development of instrument concepts for a European ELT, expanding on studies carried out as part of the ESO OWL concept. A range of instruments were chosen to demonstrate how an ELT could meet or approach the goals generated by the OPTICON science team, and used to push the specifications and requirements of telescope and adaptive optics systems. Preliminary conclusions are presented, along with a plan for further more detailed instrument design and technology developments. This activity is supported by the European Community (Framework Programme 6, ELT Design Study, contract number 011863).

NIX, the imager for ERIS: the AO instrument for the VLT

ERIS will be the next-generation AO facility on the VLT, combining the heritage of NACO imaging, with the spectroscopic capabilities of an upgraded SINFONI. Here we report on the all-new NIX imager that will deliver diffraction-limited imaging from the J to M band. The instrument will be equipped with both Apodizing Phase Plates and Sparse Aperture Masks to provide high-angular resolution imagery, especially suited for exoplanet imaging and characterization. This paper provides detail on the instrument’s design and how it is suited to address a broad range of science cases, from detailed studies of the galactic centre at the highest resolutions, to studying detailed resolved stellar populations.

Manufacturing and integration of the IFS integral spectrograph

Currently in the phase of the assembly, the Integral Field Spectrograph (IFS) is part of Sphere, which will see the first light at ESO Paranal as a VLT second generation instruments in the 2011. In this paper we will describe the main aspects in the Assembly, Integration and Testing phase (AIT) of the instrument at INAF-Osservatorio Astronomico di Padova (OAPD) laboratory at the current stage. As result of the AIT, a full set of tests and qualifications of IFS subcomponents will be discussed. These tests have been designed and realized with the purpose to obtain an accurate comparison between design goals and effective performances of the instrument.