Roland Brast

MAD status report

The European Southern Observatory together with external research Institutes is building a Multi-Conjugate Adaptive Optics Demonstrator (MAD) to perform wide field of view adaptive optics correction. The aim of MAD is to demonstrate on the sky the feasibility of the MCAO technique and to evaluate all the critical aspects in building such kind of instrument in the framework of both the 2nd generation VLT instrumentation and the 100-m Overwhelmingly Large Telescope (OWL). The MAD module will be installed at one of the VLT unit telescope in Paranal to perform on-sky observations. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD is expected to correct up to 2 arcmin field of view in K band. MAD has just started the integration phase which will be followed up by a long period of testing. In this paper we present the final design of MAD with a brief report about the status of the integration.

Resolving stellar populations outside the Local Group : MAD observations of UKS 2323-326

Aims. We present a study aimed at deriving constraints on star formation at intermediate ages from the evolved stellar populations in the dwarf irregular galaxy UKS 2323-326. These observations were also intended to demonstrate the scientific capabilities of the multi-conjugated adaptive optics demonstrator (MAD) implemented at the ESO Very Large Telescope as a test-bench of adaptive optics (AO) techniques. Methods. We perform accurate, deep photometry of the field using J and Ks band AO images of the central region of the galaxy. Results. The near-infrared (IR) colour-magnitude diagrams clearly show the sequences of asymptotic giant branch (AGB) stars, red supergiants, and red giant branch (RGB) stars down to ∼1 mag below the RGB tip. Optical-near-IR diagrams, obtained by combining our data with Hubble Space Telescope observations, provide the best separation of stars in the various evolutionary stages. The counts of AGB stars brighter than the RGB tip allow us to estimate the star formation at intermediate ages. Assuming a Salpeter initial mass

MAD star oriented: laboratory results for ground layer and multi-conjugate adaptive optics

The Multi-Conjugate Adaptive Optics Demonstrator (MAD) built by ESO with the contribution of two external consortia is a powerful test bench for proving the feasibility of Ground Layer (GLAO) and Multi-Conjugate Adaptive Optics (MCAO) techniques both in the laboratory and on the sky. The MAD module will be installed at one of the VLT unit telescope in Paranal observatory to perform on-sky observations. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors (Star Oriented and Layer Oriented) capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD is expected to correct up to 2 arcmin field of view in K band. MAD is completing the test phase in the Star Oriented mode based on Shack-Hartmann wavefront sensing. The GLAO and MCAO loops have been successfully closed on simulated atmosphere after a long phase of careful system characterization and calibration. In this paper we present the results obtained in laboratory for GLAO and MCAO corrections testing with bright guide star flux in Star Oriented mode paying also attention to the aspects involving the calibration of such a system. A short overview of the MAD system is also given.

MAPS: a turbulence simulator for MCAO

The Multi-Atmospheric Phase screens and Stars (MAPS) instrument is a powerful tool that has been developed in the framework of the ESO Multi-conjugate Adaptive optics Demonstrator project (MAD). It allows emulating a 3D evolving Paranal-like atmosphere as well as up to 12 sources in a 2 arc minutes field of view, as seen at a Nasmyth focus of one of the VLT. It will be used to perform advanced laboratory tests on MAD before its shipment to Chile. In this paper we present the opto-mechanical design of MAPS. This one simulates the characteristics of the VLT focus and achieves a high Strehl Ratio over the whole Field of View in the visible as well as in the infrared. A curved entrance plate crowded with fibers emulates various stars configurations including real sky asterisms. In order to simulate the atmosphere, three rotating Phase Screens are placed in the beam and conjugated with different altitudes. Those are glass plates dig in their surface in a way that the beam passing through is distorted as it would be by an atmospheric turbulent layer. In this poster we also present the process of research that lead to the choice of a reliable technique to imprint the aberrations into the screens, their properties and expected performance.

MAD on sky results in star oriented mode

The Multi-Conjugate Adaptive Optics Demonstrator (MAD) built by ESO with the contribution of two external consortia is a powerful test bench for proving the feasibility of Multi-Conjugate (MCAO) and Ground Layer Adaptive Optics (GLAO) techniques both in the laboratory and on the sky. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors (Star Oriented and Layer Oriented) capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD corrects up to 2 arcmin field of view in K band. After a long laboratory test phase, it has been installed at the VLT and it successfully performed on-sky demonstration runs on several astronomical targets for evaluating the correction performance under different atmospheric turbulence conditions. In this paper we present the results obtained on the sky in Star Oriented mode for MCAO and GLAO configurations and we correlate them with different atmospheric turbulence parameters. Finally we compare some of the on-sky results with numerical simulations including real turbulence profile measured at the moment of the observations.

Design and performances of the Shack-Hartmann sensor within the Active Phasing Experiment

The Shack-Hartmann Phasing Sensor (SHAPS) has been integrated in the Active Phasing Experiment (APE) at ESO. It is currently under test in the laboratory. The tests on sky are foreseen for the end of 2008, when APE will be mounted at the Nasmyth focus of one of the VLT unit telescopes. SHAPS is based on the Shack-Hartmann principle: the lenslet array is located in a plane which is optically conjugated to the Active Segmented Mirror (ASM) of APE and is composed of two types of microlenses, circular and cylindrical, which give information about the wavefront slope and the piston steps, respectively. This proceeding contains a description of SHAPS and of the algorithms implemented for the wavefront reconstruction and for the phasing. The preliminary results obtained during the laboratory tests are discussed and compared with the theoretical predictions. The performances of SHAPS at the VLT and at the European Extremely Large Telescope (E-ELT) are estimated.

Active hexagonally segmented mirror to investigate new optical phasing technologies for segmented telescopes

The primary mirror of the future European Extremely Large Telescope will be equipped with 984 hexagonal segments. The alignment of the segments in piston, tip, and tilt within a few nanometers requires an optical phasing sensor. A test bench has been designed to study four different optical phasing sensor technologies. The core element of the test bench is an active segmented mirror composed of 61 flat hexagonal segments with a size of 17 mm side to side. Each of them can be controlled in piston, tip, and tilt by three piezoactuators with a precision better than 1 nm. The context of this development, the requirements, the design, and the integration of this system are explained. The first results on the final precision obtained in closed-loop control are also presented.

ERIS: preliminary design phase overview

The Enhanced Resolution Imager and Spectrograph (ERIS) is the next-generation adaptive optics near-IR imager and spectrograph for the Cassegrain focus of the Very Large Telescope (VLT) Unit Telescope 4, which will soon make full use of the Adaptive Optics Facility (AOF). It is a high-Strehl AO-assisted instrument that will use the Deformable Secondary Mirror (DSM) and the new Laser Guide Star Facility (4LGSF). The project has been approved for construction and has entered its preliminary design phase. ERIS will be constructed in a collaboration including the Max- Planck Institut für Extraterrestrische Physik, the Eidgenössische Technische Hochschule Zürich and the Osservatorio Astrofisico di Arcetri and will offer 1 - 5 μm imaging and 1 - 2.5 μm integral field spectroscopic capabilities with a high Strehl performance. Wavefront sensing can be carried out with an optical high-order NGS Pyramid wavefront sensor, or with a single laser in either an optical low-order NGS mode, or with a near-IR low-order mode sensor. Due to its highly sensitive visible wavefront sensor, and separate near-IR low-order mode, ERIS provides a large sky coverage with its 1’ patrol field radius that can even include AO stars embedded in dust-enshrouded environments. As such it will replace, with a much improved single conjugated AO correction, the most scientifically important imaging modes offered by NACO (diffraction limited imaging in the J to M bands, Sparse Aperture Masking and Apodizing Phase Plate (APP) coronagraphy) and the integral field spectroscopy modes of SINFONI, whose instrumental module, SPIFFI, will be upgraded and re-used in ERIS. As part of the SPIFFI upgrade a new higher resolution grating and a science detector replacement are envisaged, as well as PLC driven motors. To accommodate ERIS at the Cassegrain focus, an extension of the telescope back focal length is required, with modifications of the guider arm assembly. In this paper we report on the status of the baseline design. We will also report on the main science goals of the instrument, ranging from exoplanet detection and characterization to high redshift galaxy observations. We will also briefly describe the SINFONI-SPIFFI upgrade strategy, which is part of the ERIS development plan and the overall project timeline.

Shack-Hartmann sensor for the active phasing experiment

The purpose of the Active Phasing Experiment, designed at ESO, is to validate wavefront control concepts for ELT class telescopes. This instrument includes an Active Segmented Mirror, located in a pupil image. It will be mounted at a Nasmyth focus of one of the unit telescopes of the ESO VLT. The Active Phasing Experiment will compare four types of phasing sensor. One of them is based on the Shack-Hartmann principle. The lenslets in the array will be placed on intersegment borders for the measurement of piston steps, as well and inside the subapertures defined by the segments for the measurement of local slopes generated by the segments and the telescope optics. The paper describes the design of the sensor optics and the lenslet array, and discusses the expected performance of the sensor under laboratory conditions and in the telescope.

The ERIS adaptive optics system

The Enhanced Resolution Imager and Spectrograph (ERIS) is the new Adaptive Optics based instrument for ESO’s VLT aiming at replacing NACO and SINFONI to form a single compact facility with AO fed imaging and integral field unit spectroscopic scientific channels. ERIS completes the instrument suite at the VLT adaptive telescope. In particular it is equipped with a versatile AO system that delivers up to 95% Strehl correction in K band for science observations up to 5 micron It comprises high order NGS and LGS correction enabling the observation from exoplanets to distant galaxies with a large sky coverage thanks to the coupling of the LGS WFS with the high sensitivity of its visible WFS and the capability to observe in dust embedded environment thanks to its IR low order WFS. ERIS will be installed at the Cassegrain focus of the VLT unit hosting the Adaptive Optics Facility (AOF). The wavefront correction is provided by the AOF deformable secondary mirror while the Laser Guide Star is provided by one of the four launch units of the 4 Laser Guide Star Facility for the AOF. The overall layout of the ERIS AO system is extremely compact and highly optimized: the SPIFFI spectrograph is fed directly by the Cassegrain focus and both the NIX’s (IR imager) and SPIFFI’s entrance windows work as visible/infrared dichroics. In this paper we describe the concept of the ERIS AO system in detail, starting from the requirements and going through the estimated performance, the opto-mechanical design and the Real-Time Computer design.