Guido Agapito

Large Binocular Telescope Adaptive Optics System: new achievements and perspectives in adaptive optics

The Large Binocular Telescope (LBT) is a unique telescope featuring two co-mounted optical trains with 8.4m primary mirrors. The telescope Adaptive Optics (AO) system uses two innovative key components, namely an adaptive secondary mirror with 672 actuators and a high-order pyramid wave-front sensor. During the on-sky commissioning such a system reached performances never achieved before on large ground-based optical telescopes. Images with 40mas resolution and Strehl Ratios higher than 80% have been acquired in H band (1.6 μm). Such images showed a contrast as high as 10-4. Based on these results, we compare the performances offered by a Natural Guide Star (NGS) system upgraded with the state-of-the-art technology and those delivered by existing Laser Guide Star (LGS) systems. The comparison, in terms of sky coverage and performances, suggests rethinking the current role ascribed to NGS and LGS in the next generation of AO systems for the 8-10 meter class telescopes and Extremely Large Telescopes (ELTs).

Natural guide star adaptive optics systems at LBT: FLAO commissioning and science operations status

This paper summarizes the activities and the principal results achieved during the commissioning of the two Natural Guide Star (NGS) AO systems called FLAO#1 & 2 installed at the bent Gregorian focal stations of the 2x8.4m Large Binocular Telescope (LBT). The commissioning activities of FLAO#1 took place in the period February 2010 - October 2011, while FLAO#2 commissioning started in December 2011 and should be completed by November 2012. The main results of the commissioning campaign are presented in terms of the H-band Strehl Ratio values achieved under different observing conditions. We will also describe the automatic procedures to configure and set-up the FLAO systems, and in particular the modal gain optimization procedure, which has been proven to be a very important one in achieving the nominal performance. Finally, some of the results achieved in two science runs using the near infra-red camera PISCES are briefly highlighted.

First light AO (FLAO) system for LBT: performance analysis and optimization

We will present in this paper the performance analysis and optimization of the First Light AO (FLAO) system of the Large Binocular Telescope (LBT). The system comprises an adaptive secondary mirror (ASM) with 672 actuators (LBT672a unit) and a pyramid wavefront sensor (PWFS) with adjustable sampling of the telescope pupil from 30×30 down to 4×4 subapertures. The performances have been estimated by means of end-to-end simulations, scanning a range of reference star magnitudes and looking for the optimal set of parameters maximizing the on-axis Strehl Ratio. Specific additional error sources have been accounted for and analyzed separately, such as mis-registration errors, mis-calibration issues, and the effect of telescope vibrations. Taking into account the considered error sources we defined the baseline and goal performances of the FLAO system. The acceptance test of the FLAO system took place in December 2009, demonstrating actual FLAO performances between baseline and goal estimates. The commissioning of the FLAO system to the LBT telescope is currently ongoing until December 2010.

Observer-Based Control Techniques for the LBT Adaptive Optics under Telescope Vibrations

This paper addresses the application of observer-based control techniques for the adaptive optics system of the LBT telescope. In such a context, attention is focused on the use of Kalman and H∞ filters to estimate the temporal evolution of phase perturbations due to the atmospheric turbulence and the telescope vibrations acting on tip/tilt modes. We shall present preliminary laboratory experiments carried out at the Osservatorio Astrofisico di Arcetri using the Kalman filter.

Wavefront sensor design for the GMT natural guide star AO system

The paper presents the preliminary design of theNat ural Guide Star Wavefront Sensor for the single conjugate AO system of the GMT telescope. The NGS Wavefront Sensor (NGWS), already identified as a pyramid sensor, will be in charge of the entire wavefront error measurement namely atmospheric turbulence and telescope aberrations, including the segment differential piston error. The paper describes the WFS opto-mechanical design with particular emphasis on the WFS board. Numerical simulations of the GMT NGS AO system are performed taking into account the main characteristics of the considered WFS unit. The simulations take into account correction of the atmospheric perturbation and control of the differential pistons of the GMT segments.

Automatic Tuning of the Internal Position Control of an Adaptive Secondary Mirror

One of the key components of an Adaptive Optics system is the deformable mirror. This mirror can correct the atmospheric turbulence effects by changing its shape. In the last years Adaptive Secondary Mirrors (ASM) have been developed and the Large Binocular Telescope (LBT) will be soon equipped with two ASMs. Each LBT ASM unit has 672 voice-coil force actuators to change the shape of the mirror shell. Because the actuators apply force, an internal position control is required. The LBT ASM internal control uses a local feedback of position and velocity, then the control law for each actuator has two characteristic parameters which define the closed-loop shell dynamics. In this paper, an analysis of the dynamical behaviour of the ASM under the proposed control law is provided. Then an algorithm is suggested that, based on a simplified model of the shell dynamics, tunes the controller parameters by means of an automatic procedure, as a replacement for a manual procedure based on the operator skill.

SOUL: The Single conjugated adaptive Optics Upgrade for LBT

We present here SOUL: the Single conjugated adaptive Optics Upgrade for LBT. Soul will upgrade the wavefront sensors replacing the existing CCD detector with an EMCCD camera and the rest of the system in order to enable the closed loop operations at a faster cycle rate and with higher number of slopes. Thanks to reduced noise, higher number of pixel and framerate, we expect a gain (for a given SR) around 1.5–2 magnitudes at all wavelengths in the range 7.5 70% in I-band and 0.6asec seeing) and the sky coverage will be multiplied by a factor 5 at all galactic latitudes. Upgrading the SCAO systems at all the 4 focal stations, SOUL will provide these benefits in 2017 to the LBTI interferometer and in 2018 to the 2 LUCI NIR spectro-imagers. In the same year the SOUL correction will be exploited also by the new generation of LBT instruments: V-SHARK, SHARK-NIR and iLocater.

LBT observations of the HR 8799 planetary system - First detection of HR 8799e in H band

We have performed H and KS band observations of the planetary system around HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES Camera. The excellent instrument performance (Strehl ratios up to 80% in H band) enabled the detection of the innermost planet, HR 8799e ,a tH band for the first time. The H and KS magnitudes of HR 8799e are similar to those of planets c and d, with planet e being slightly brighter. Therefore, HR 8799e is likely slightly more massive than c and d .W e also explored possible orbital configurations and their orbital stability. We confirm that the orbits of planets b, c and e are consistent with being circular and coplanar; planet d should have either an orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c. Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion resonances with c and d, while coplanar and circular orbits are allowed for a 5:2 resonance. The analysis of dynamical stability shows that the system is highly unstable or chaotic when planetary masses of about 5 MJ for b and 7 MJ for the other planets are adopted. Significant regions of dynamical stability for timescales of tens of Myr are found when adopting planetary masses of about 3.5, 5, 5, and 5 MJ for HR 8799b, c, d ,a nde respectively. These masses are below the current estimates based on the stellar age (30 Myr) and theoretical models of substellar objects.

Optimal control techniques for the adaptive optics system of the LBT

In this paper we will discuss the application of different optimal control techniques for the adaptive optics system of the LBT telescope which comprises a pyramid wavefront sensor and an adaptive secondary mirror. We have studied the application of both the Kalman and the H∞ filter to estimate the temporal evolution of the phase perturbations due to the atmospheric turbulence and the telescope vibrations. We have evaluated the performance of these control techniques with numerical simulations in preparation of the laboratory tests that will be carried out in the Arcetri laboratories.

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.