AO systems aim at detecting and correcting for optical distortions induced by atmospheric turbulences. They are also extremely sensitive to extraneous sources of perturbation such as vibrations, which degrade the performance. The Gemini South telescope has currently two main AO systems: the Gemini Multi Conjugated AO System GeMS and the Gemini Planet Imager GPI. GeMS is operational and regularly used for science observation delivering close to diffraction limit resolution over a large field of view (85×85 arcsec2). Performance limitation due to the use of an integrator for tip-tilt control is here explored. In particular, this type of controller does not allow for the mitigation of vibrations with an arbitrary natural frequency. We have thus implemented a tip-tilt Linear Quadratic Gaussian (LQG) controller with different underlying perturbation models: (i) a sum of autoregressive models of order 2 identified from an estimated power spectrum density (s-AR2) of the perturbation,1 already tested on CANARY2 and routinely used on SPHERE;3 (ii) cascaded ARMA models of order 2 identified using prediction error minimization (c-PEM) as proposed in.4, 5 Both s-AR2 and c-PEM were parameterized to produce tip or tilt state-space models up to order 20 and 30 respectively. We discuss the parallelized implementation in the real time computer and the expected performance. On-sky tests are scheduled during the November 2016 run or the January 2017 run.
ELTs equipped with MCAO systems will be powerful astrometric tools in the next two decades. With sparse-field precisions exceeding 30 uas for V > 18, the ELTs will surpass even GAIA's per-epoch precision for faint stars (V > 12). We present results from an ongoing astrometry program with Gemini GeMS and discuss synergies with WFIRST and GAIA. First, we present a fit to the relative orbit of the individual L/T components of Luhman16 AB, the nearest brown dwarf binary known. Exploiting GeMS' wide field of view to image reference stars, we are able to track the relative motion to better than 0.2 mas. We find that a mutual Keplerian orbit with no perturbing planets fits the binary separation to within the measurement errors, ruling out companions down to 14 earth masses for certain orbits and periods.
GeMS, the Gemini South MCAO System, has now been in operation for 3 years with the near infrared imager GSAOI. We first review the performance obtained by the system, the science cases and the current operational model. In the very near future, GeMS will undergo a profound metamorphosis, as we will integrate a new NGS wavefront sensor, replace the current 50W laser with a more robust one and prepare for a new operational model where operations will shift from the mountain to the base facility. Along this major evolution, we are also presenting several improvements on the loop control, calibrations and automatization of this complex system. We discuss here the progress of the different upgrades and what we expect in terms of performance improvements and operational efficiency.
AutoCAD, Zemax Optic Studio 15, and Interactive Data Language (IDL) with the Proper Library are used to computationally model and test a diffractive mask (DiM) suitable for use in the Gemini Multi-Conjugate Adaptive Optics System (GeMS) on the Gemini South Telescope. Systematic errors in telescope imagery are produced when the light travels through the adaptive optics system of the telescope. DiM is a transparent, flat optic with a pattern of miniscule dots lithographically applied to it. It is added ahead of the adaptive optics system in the telescope in order to produce diffraction spots that will encode systematic errors in the optics after it. Once these errors are encoded, they can be corrected for. DiM will allow for more accurate measurements in astrometry and thus improve exoplanet detection. The mechanics and physical attributes of the DiM are modeled in AutoCAD. Zemax models the ray propagation of point sources of light through the telescope. IDL and Proper simulate the wavefront and image results of the telescope. Aberrations are added to the Zemax and IDL models to test how the diffraction spots from the DiM change in the final images. Based on the Zemax and IDL results, the diffraction spots are able to encode the systematic aberrations.
NGS2 is an upgrade for the multi-natural guide star tip-tilt & plate scale wavefront sensor for GeMS (Gemini Multi-Conjugate Adaptive Optics system). It uses a single Nüvü HNü-512 Electron-Multiplied CCD array that spans the entire GeMS wavefront sensor focal plane. Multiple small regions-of-interest are used to enable frame rates up to 800Hz. This set up will improve the optical throughput with respect to the current wavefront sensor, as well as streamline acquisition and allow for distortion compensation.
The Gemini Multi-conjugate adaptive optics System (GeMS) at the Gemini South telescope in Cerro Pachon is the first sodium Laser Guide Star (LGS) adaptive optics (AO) system with multiple guide stars. It uses five LGSs and two deformable mirrors (DMs) to measure and compensate for distortions induced by atmospheric turbulence. After its 2012 commissioning phase, it is now transitioning into regular operations. Although GeMS has unique scientific capabilities, it remains a challenging instrument to maintain, operate and upgrade. In this paper, we summarize the latest news and results. First, we describe the engineering work done this past year, mostly during our last instrument shutdown in 2013 austral winter, covering many subsystems: an erroneous reconjugation of the Laser guide star wavefront sensor, the correction of focus field distortion for the natural guide star wavefront sensor and engineering changes dealing with our laser and its beam transfer optics. We also describe our revamped software, developed to integrate the instrument into the Gemini operational model, and the new optimization procedures aiming to reduce GeMS time overheads. Significant software improvements were achieved on the acquisition of natural guide stars by our natural guide star wavefront sensor, on the automation of tip-tilt and higher-order loop optimization, and on the tomographic non-common path aberration compensation. We then go through the current operational scheme and present the plan for the next years. We offered 38 nights in our last semester. We review the current system efficiency in term of raw performance, completed programs and time overheads. We also present our current efforts to merge GeMS into the Gemini base facility project, where night operations are all reliably driven from our La Serena headquarter, without the need for any spotter. Finally we present the plan for the future upgrades, mostly dedicated toward improving the performance and reliability of the system. Our first upgrade called NGS2, a project lead by the Australian National University, based a focal plane camera will replace the current low throughput natural guide wavefront sensor. On a longer term, we are also planning the (re-)integration of our third deformable mirror, lost during the early phase of commissioning. Early plans to improve the reliability of our laser will be presented.
We measure the long-term systematic component of the astrometric error in the GeMS MCAO system as a function of field radius and Ks magnitude. The experiment uses two epochs of observations of NGC 1851 separated by one month. The systematic component is estimated for each of three field of view cases (15'' radius, 30'' radius, and full field) and each of three distortion correction schemes: 8 DOF/chip + local distortion correction (LDC), 8 DOF/chip with no LDC, and 4 DOF/chip with no LDC. For bright, unsaturated stars with 13 < Ks < 16, the systematic component is < 0.2, 0.3, and 0.4 mas, respectively, for the 15'' radius, 30'' radius, and full field cases, provided that an 8 DOF/chip distortion correction with LDC (for the full-field case) is used to correct distortions. An 8 DOF/chip distortion-correction model always outperforms a 4 DOF/chip model, at all field positions and magnitudes and for all field-of-view cases, indicating the presence of high-order distortion changes. Given the order of the models needed to correct these distortions (~8 DOF/chip or 32 degrees of freedom total), it is expected that at least 25 stars per square arcminute would be needed to keep systematic errors at less than 0.3 milliarcseconds for multi-year programs. We also estimate the short-term astrometric precision of the newly upgraded Shane AO system with undithered M92 observations. Using a 6-parameter linear transformation to register images, the system delivers ~0.3 mas astrometric error over short-term observations of 2-3 minutes.
During the 2012 commissioning of the Gemini MCAO System (GeMS) in Gemini South Observatory, we briefly explored the performance improvement brought by pairing GeMS with the Gemini Multi-Object Spectrograph (GMOS), compared to GMOS in natural seeing mode. GMOS is an instrument sensitive in the visible band with imaging and spectroscopic capabilities, hence pushing MCAO toward the visible, a mode for which it was not specifically designed.
We report in this paper the first results obtained with the GeMS +GMOS pair. Several globular clusters were observed in imaging mode only. We have derived performance in term of FWHM and determined the improvement against natural seeing. We also obtain photometric, relative and absolute astrometric precision for the AO enhanced images. We also studied the influence of the NGS constellation on the photometric performance.
Finally, we also looked at the expected performance of the GeMS+GMOS system once the CCD upgrade, scheduled during 2014, will occur.
CANARY is an on-sky Laser Guide Star (LGS) tomographic AO demonstrator that has been in operation at the 4.2m William Herschel Telescope (WHT) in La Palma since 2010. In 2013, CANARY was upgraded from its initial configuration that used three off-axis Natural Guide Stars (NGS) through the inclusion of four off-axis Rayleigh LGS and associated wavefront sensing system. Here we present the system and analysis of the on-sky results obtained at the WHT between May and September 2014. Finally we present results from the final ‘Phase C’ CANARY system that aims to recreate the tomographic configuration to emulate the expected tomographic AO configuration of both the AOF at the VLT and E-ELT.
Many concepts of Wide Field AO (WFAO) systems are under development, especially for Extremely Large Tele scopes (ELTs) instruments. Multi-Object Adaptive Optics (MOAO) is one of these WFAO concepts, well suited to high redshifts galaxies observations in very wide Field of View (FoV). The E-ELT instrument EAGLE will use this approach. CANARY, the on-sky pathfinder for MOAO, has obtained the first compensated images on Natural Guide Stars (NGSs) at the William Herschel Telescope in September 2010. We present in this paper numerical and experimental validations of a Linear Quadratic Gaussian (LQG) control. This is an appealing strategy that provides an optimal control in the sense of minimum residual phase variance. It also provides a unified formalism that allows accounting for multi WaveFront Sensors (WFSs) channels, both on Laser Guide Stars (LGSs) and NGSs, and for various disturbance sources (turbulence, vibrations). We show how the specific MOAO CANARY configuration can be embedded in a state-space framework. We present experimental laboratory validations that demonstrate the gain brought by tomographic LQG control for CANARY, together with comparative simulations. Model identification necessary for a robust on-sky operation is discussed.
We present in this paper an analysis of several tip-tilt on-sky data registered on adaptive optics systems installed on different telescopes (Gemini South, William Herschel Telescope, Large Binocular Telescope, Very Large Tele scope, Subaru). Vibration peaks can be detected, and it is shown that their presence and location may vary, and that their origin is not always easy to determine. Mechanical solution that have been realized to mitigate vibrations are presented. Nevertheless, residual vibrations may still affect the instruments' performance, ranging from narrow high frequency vibration peaks to wide low frequency windshake-type perturbations. Power Spectral Densities (PSDs) of on-sky data are presented to evidence these features. When possible, indications are given regarding the gain in performance that could be achieved with adequate controllers accounting for vibration mitigation. Two examples of controller identification and design illustrate their ability to compensate for various types of disturbances (turbulence, windshake, vibration peaks, ...),showing a significant gain in performance.
Perturbations affecting image formation on ground-based telescopes are composed of signals that are not only generated by the atmosphere. They often include vibrations induced by wind excitation on the system's structure, or induced by other sources of excitation like cryo-coolers, shutters, etc.
Using state-space control design techniques (e.g., LQG control), efficient perturbation compensation can be obtained in adaptive optics systems. This requires in return an accurate dynamical perturbation model with manageable complexity. The purpose of this paper is to investigate how tip/ tilt state-space models can be constructed and identified from wavefront sensor (WFS) measurements and used for tip/ tilt correction. Several off-the-shelf time-domain identification approaches are considered, ranging from techniques such as subspace identification to extended Kalman filter.
Results are compared with controllers that do not account for vibrations, like an integrator or an MMSE reconstructor. Performance improvement is illustrated by replay with on-sky data sets from Gemini South (GeMS and Altair).