Fausto Cortecchia

VST project: technical overview

The VST (Very Large Telescope Survey Telescope) is an 2.6 m class Alt-Az telescope which will be installed in the European Southern Observatory (ESO) Paranal site, Chile. It has been designed by the Technology Working Group of the Astronomical Observatory of Capodimonte, Italy. The VST is an 1 degree(s) X 1 degree(s) wide-field imaging facility planned to supply databases for the ESO VLT science and carry out stand-alone observations in the UV to I spectral range starting in the year 2001. All the solutions adopted in the VST design comply to the ESO VLT standards. This paper reports a technical overview of the telescope design.

Preparing for the phase B of the E-ELT MCAO module project

The Multi-Conjugate Adaptive Optics module for the European Extremely Large Telescope has been designed to achieve uniform compensation of the atmospheric turbulence effects on a wide field of view in the near infrared. The design realized in the Phase A of the project is undergoing major revision in order to define a robust baseline in view of the next phases of the project. An overview of the on-going activities is presented.

Cambridge OH suppression instrument (COHSI): status after first commissioning run

COHSI was successfully commissioned at the United Kingdom IR Telescope on Mauna Kea during a seven night observing run which coincided with this conference. Here we briefly describe the instrument and give a preliminary report on its performance at this time. The suppression optics and masks worked extremely well and the instrument background was found to be very low.

Optical design of the post focal relay of MAORY

The Multi Conjugate Adaptive Optics RelaY (MAORY) is foreseen to be installed at the straight through focus over the Nasmyth platform of the future Extremely Large Telescope (ELT). MAORY has to re-image the telescope focal plane with diffraction limited quality and low geometric distortion, over a field of view of 20 arcsec diameter, for a wavelength range between 0.8 μm and 2.4 μm. Good and uniform Strehl ratio, accomplished with high sky coverage, is required for the wide field science. Two exit ports will be fed by MAORY. The first one is for a wide field Camera that is supposed to be placed on a gravity invariant port with an unvignetted FoV of 53 arcsec x 53 arcsec where diffraction limited optical quality (< 54nm RMS of wavefront error at the wavelength of 1 μm) and very low field distortion (< 0.1% RMS) must be delivered. The requirements regarding the optical quality, distortion and optical interfaces, together with the desire of reducing the number of reflecting surfaces (and consequently the thermal background), optics wavefront error (WFE), overall size, weight and possibly cost, drove the design to have 2 Deformable Mirrors (DMs) with optical power. The Post Focal Relay (PFR) is also required to split the 589 nm wavelength light of the Laser Guide Stars (LGS), used for high order wavefront sensing, by means of a dichroic that lets the light of 6 LGSs, arranged on a circle of about 90 arcsec diameter, pass through and reflects science beam. Behind the dichroic an objective creates the LGS image plane for the WFSs channel. We present in this paper the optical design and the tolerance analysis of the PFR and the objective. The tolerance analysis concerning the manufacturing and the alignment precision is also shown.

MAORY: adaptive optics module for the E-ELT

MAORY is one of the four instruments for the E-ELT approved for construction. It is an adaptive optics module offering two compensation modes: multi-conjugate and single-conjugate adaptive optics. The project has recently entered its phase B. A system-level overview of the current status of the project is given in this paper.

The numerical simulation tool for the MAORY multiconjugate adaptive optics system

The Multiconjugate Adaptive Optics RelaY (MAORY) is and Adaptive Optics module to be mounted on the ESO European-Extremely Large Telescope (E-ELT). It is an hybrid Natural and Laser Guide System that will perform the correction of the atmospheric turbulence volume above the telescope feeding the Multi-AO Imaging Camera for Deep Observations Near Infrared spectro-imager (MICADO). We developed an end-to-end Monte- Carlo adaptive optics simulation tool to investigate the performance of a the MAORY and the calibration, acquisition, operation strategies. MAORY will implement Multiconjugate Adaptive Optics combining Laser Guide Stars (LGS) and Natural Guide Stars (NGS) measurements. The simulation tool implement the various aspect of the MAORY in an end to end fashion. The code has been developed using IDL and use libraries in C++ and CUDA for efficiency improvements. Here we recall the code architecture, we describe the modeled instrument components and the control strategies implemented in the code.

Numerical simulations of MAORY MCAO module for the ELT

MAO (MAORY Adaptive Optics) is the a developed numerical simulation tool for adaptive optics. It was created especially to simulate the performance of the MAORY MCAO module of the Extremely Large Telescope. It is a full end-to-end Monte-Carlo code able to perform different flavors of adaptive optics simulation. We used it to investigate the performance of a the MAORY and some specific issue related to calibration, acquisition and operation strategies. As, MAORY, MAO will implement Multi-conjugate Adaptive Optics combining Laser Guide Stars (LGS) and Natural Guide Stars (NGS) measurements. The implementation of the reference truth WFS completes the scheme. The simulation tool implements the various aspect of the MAORY in an end to end fashion. The code has been developed using IDL and use libraries in C++ and CUDA for efficiency improvements. Here we recall the code architecture, we describe the modeled instrument components and the control strategies implemented in the code.

MAORY optical design analysis and tolerances

MAORY (Multi-conjugate Adaptive Optics RelaY) will be the multi-conjugate adaptive optics module for the ELT first light. MAORY is a post focal relay optics and supports the MICADO imager and spectrograph. The tolerance process of MAORY is one of the most important step in the instrument design since it is intended to ensure that MAORY requested performances are satisfied when the final assembled instrument is operative. At the end, the assignment of tolerances to the various opto-mechanical parameters should be a trade-off between final cost of the system and its resulting performances. This paper describes the logic behind the tolerance analysis starting from definition of quantitative figures of merit for MAORY requirements and ending with estimation of MAORY performances perturbed by opto-mechanical tolerances. The method used to estimate tolerances takes care of compensation of errors during assembly/alignment procedure and uses a Root-Sum-Squared (RSS) merit function to combine independent error contributions. There are two requirements that limit the allowable changes of opto-mechanical parameters. The Root-Mean-Squared wavefront error (RMS WFE) and the optical distortion. The first one must satisfy diffraction limited performance over the MICADO Field-of-View (FoV) while the second one must satisfy high astrometric accuracy and precision. As criterion for tolerancing, the defined merit function considers the RMS wavefront referred to star centroids and adds boundary constraints on the compensators and geometric distortion in MICADO FoV. To evaluate the impact of tolerances on astrometry, a Monte Carlo approach was followed validating the expected performances from a pure opto-mechanical point of view.

Precise alignment method for MAORY

MAORY (Multi-conjugate Adaptive Optics RelaY) and MICADO (MCAO Imaging CamerA for Deep Observations) will perform the science in the Multi-conjugate Adaptive Optics mode of the ELT (Extremely Large Telescope). One of their goals is the multi-object differential astrometry which requires low optical distortion and diffraction limited aberrations. To align MAORY, an automate method will be used during the integration of the instrument and could be part of the calibration strategy at the ELT site. This paper describes the method and the ray-tracing simulations carried out to validate the algorithm. Even in presence of different error sources, the method works in a large range of misalignments bringing the system close to the nominal performances.

MAORY for ELT: preliminary mechanical design of the support structure

MAORY (Multi Conjugate Adaptive Optics RelaY) is one of the four instruments for the ELT (Extremely Large Telescope) approved for construction. It is an adaptive optics module able to compensate the wavefront disturbances affecting the scientific observations, achieving high strehl ratio and high sky coverage. MAORY will be located on the straight-through port of the telescope Nasmyth platform and shall re-image the telescope focal plane to a wide field camera (MICADO) and a possible future second instrument. A trade-off study among different mechanical design options for the main mechanical structure has been carried out. This paper outlines an overview of the mechanical design that gives a better result in terms of stability, vibrations and manufacturing.