Cookies

We use cookies to ensure that we give you the best experience on our website. You can change your cookie settings at any time. Otherwise, we'll assume you're OK to continue.

Centre for Advanced Instrumentation

CANARY

CANARY is an open-loop Adaptive Optics system that will be deployed on the 4.2m William Herschel Telescope in La Palma from July 2010. CANARY will use multiple laser guide stars and deformable mirrors and will be the instrument that provides the first on-sky test of combined wide-field LGS tomography and open-loop AO control. On-sky validation of these combined techniques will be performed with the goal of emulating a single channel of the proposed E-ELT MOAO instrument, MOSAIC, albeit at 1/10th scale. The MOSAIC webpages contain many examples of the type of science that could be performed with such an MOAO instrument on the E-ELT.

Building and testing an MOAO instrument with the same configuration as MOSAIC, with multiple DMs and both natural and artificial (Laser) reference stars is undoubtedly complex. In order to reduce the overall difficulty of building and testing such a system, the CANARY team have adopted a phased approach to CANARY development with on-sky runs over 5 years from July 2010.

  • Phase A (2010): 3 x NGS WFS tomography and a single low-order DM
  • Phase B (2012): 4 x LGS WFS tomography and a single low-order DM
  • Phase C (2013-2015): 4 x LGS WFS tomography and a woofer-tweeter DM configuration
  • Phase D (2016-): 1 x off-axis sodium LGS for ELT-scale WFS testing

Status updates

23rd August 2016

The latest upgrade to the CANARY adaptive optics system was commissioned between the 19th and 25th July with the installation of the European Southern Observatory’s ‘Wendelstein’ sodium Laser Guide Star Unit (WLGSU) in a new custom-built laser enclosure next to the 4.2m William Herschel Telescope in La Palma.

The 20 Watt 589nm laser was used to excite fluorescence of a thick layer of sodium atoms which are typically observed between 80 and 100km above sea level. The wavefront distortions caused by the turbulent atmosphere in the returned laser light were measured using CANARY 150 times a second and will be compared to the distortions measured from a constellation of background stars.

Unlike other LGS systems in operation, the laser is situated 40m off-axis from the WHT, recreating the LGS geometry expected for the upcoming European Extremely Large Telescope (http://www.eso.org/sci/facilities/eelt/) and turning the WHT into a 4.2m diameter segment of this giant telescope. Recreating this geometry is important because the variable thickness and density of the sodium layer means that the LGS suffers from 20-30 arcseconds of perspective elongation in the CANARY wavefront sensors. LGS on existing 8-10m class telescopes typically observe 2-5 arcseconds of elongation, which is inside the isoplanatic patch size of the atmosphere. The first generation of instruments proposed for the E-ELT all rely on adaptive optics system to fulfil their scientific goals, and errors in the wavefront sensing coming from the highly-elongated LGS will affect performance. There are several proposed methods for wavefront sensing from such an elongated LGS, but these have never been investigated on-sky in real-world environment

Image of the transportable ‘Wendelstein’ sodium laser guide star unit in its new enclosure just after sunset. The Nordic Optical Telescope can be seen in the background.

To ensure a measurement of the LGS wavefront that can be disentangled from the effects of density variations in the sodium layer the 2.5m INT is also being used to observe the LGS. The INT is 420m off-axis from the LGS launch location resulting in elongations of up to 5 arcminutes. A 6.5 arcminute field of view laser plume imager running at 150Hz (synchronised with the CANARY wavefront sensors) was used to provide a high vertical resolution image of the plume that can be used to calibrate the CANARY wavefront sensor measurements. The INT telescope control system was integrated with the CANARY systems to allow pointing, focus and rotation commands to be offloaded automatically from either CANARY or the plume imager, turning the INT into a robotic (albeit monitored!) telescope. Simultaneous measurements of LGS return flux and atmospheric transmission are also provided by the WLGSU via an auxiliary 35cm diameter telescope installed next to the laser enclosure.

The CANARY AO demonstrator at the WHT with ESO’s WLGSU is the only facility worldwide capable of performing a comprehensive field investigation of the effects of extreme LGS elongation on AO performance. Results and analysis from CANARY will feed directly into the next generation of ELT scale AO instrumentation.

CANARY Phase D is an international collaboration consisting of Durham University, Observatoire de Paris, European Southern Observatory, INAF - Osservatorio Astronomico di Roma, Instituto de Astrofisica de Canarias, UK Astronomy Technology Centre and the Isaac Newton Group of Telescopes. CANARY is funded in the UK by STFC through the UK E-ELT program (Ref ST/M007669/1), by CNRS/INSU and Observatoire de Paris in France and by the European Commission OPTICON project (EC FP7 grant agreement 312430). The WLGSU is funded by ESO. The CANARY and LGS teams would like to thank the ING and IAC for their support before and during the run.

Synchronised images from the CANARY on-axis laser and natural guide star wavefront sensors showing the difference between non-elongated and elongated sources as observed by the 4.2m William Herschel Telescope.

Image of the sodium LGS, Rayleigh plume and background natural guide star asterism using the auxiliary 35cm telescope situated 10m off-axis from the laser guide star launch location.

CANARY Phase D is an international collaboration consisting of Durham University, Observatoire de Paris, European Southern Observatory, INAF - Osservatorio Astronomico di Roma, Instituto de Astrofisica de Canarias, UK Astronomy Technology Centre and the Isaac Newton Group of Telescopes. CANARY is funded in the UK by STFC through the UK E-ELT program (Ref ST/M007669/1), by CNRS/INSU and Observatoire de Paris in France and by the European Commission OPTICON project (EC FP7 grant agreement 312430). The WLGSU is funded by ESO. The CANARY and LGS teams would like to thank the ING and IAC for their support before and during the run.

More information:

“Proposal for a field experiment of elongated Na LGS wave-front sensing in the perspective of the E-ELT”, G. Rousset et al, Proc. SPIE 9148, Adaptive Optics Systems IV, 91483M (2014); doi:10.1117/12.2056366

“MOAO first on-sky demonstration with CANARY”, E. Gendron et al. A&A 529, L2 http://www.aanda.org/component/content/article?id=699

“Comparison between observation and simulation of sodium LGS return flux with a 20W CW laser on Tenerife”, R. Holzlöhner et al, Proc. SPIE 9909, Adaptive Optics Systems V, 99095E (2016); doi: 10.1117/12.2233072

"The ESO transportable LGS Unit for measurements of the LGS photon return flux and other experiments", Bonaccini Calia et al, Proc. SPIE 8450, (2012); doi:10.1117/12.926898, https://www.eso.org/sci/libraries/SPIE2012/8450-61.pdf

“CANARY: the on-sky NGS/LGS MOAO demonstrator for EAGLE”, Richard M. Myers et al, Proc. SPIE 7015, Adaptive Optics Systems, 70150E (2008); doi:10.1117/12.789544