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, EAGLE, albeit at 1/10th scale. The EAGLE 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 EAGLE, 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 (2013-2014): 4 x LGS WFS tomography and a woofer-tweeter DM configuration
In order to allow the 3 CANARY phases to be conducted with only minor modifications and upgrades required, the CANARY design is based around a set of reconfigurable optical modules. By re-arranging these modules, different instrumental configurations can be achieved for the three phases without redesigning the entire system.
The principal optomechanical modules are shown in their phase A (3 x NGS) configuration in the figure above. The optical layout of the main AO path modules is shown below.
The WFSs and DMs are linked together by the Real Time Control System (RTCS) which links to the rest of CANARY through the Instrument Control System (ICS). You can read more about both the RTCS and ICS under the 'Projects' heading.
Monte-Carlo simulations of the CANARY system were performed at Durham and at the Observatiore de Paris to determine the level of correction that could be achieved using standard asterisms and representative turbulence profiles for La Palma. For a 3-star triangular NGS asterism (30" radius) CANARY will achieve a Strehl ratio of approximately 0.22 at a wavelength of 1.65µm (323nm RMS error). The major source of error within this system is due to the sampling of the highest layers of turbulence at an altitude of approximately 15km above the telescope. With the defined asterism on a 4.2m diameter telescope, the distance between two of the projected pupils at 15km is approximately 3.8m. If the pupils do not overlap, then no tomographic information can be derived from this layer thereby degrading performance. Other significant sources of error within the system are the DM fitting and temporal errors.
In order to measure and characterise all error sources within CANARY the system contains many calibration and alignment tools that would not normally be included with a closed-loop facility-class instrument. One of the most critical components are the turbulence profilers that are able to characterise the vertical distribution of turbulence above the telescope. In addition to the WHT's own turbulence profilers, two SLODAR systems will be used. The first SLODAR system will use the information from the CANARY WFSs, while a second external SLODAR system will be installed on the WHT roof to measure the turbulence up to 20km.
Unlike most instruments deployed on large astronomical telescopes, the name CANARY isn't an acronym for anything. The CANARY name harks back to the first proposed MOAO instrument for one of the 8m-diameter VLTs, called FALCON. The final phase of CANARY is also demonstrating a single MOAO channel for the proposed EAGLE instrument on the future 42m diameter European ELT.
The avian-related naming scheme for MOAO instruments has recently been extended to include RAVEN, an MOAO instrument being developed by HIA. Other on-sky MOAO instruments include ViLLAGES and VOLT.
CANARY is a collaborative project between several institutions in the UK, France and Spain (shown below) and is funded by STFC (under the UK E-ELT Design Study), ANR Mauii, INSU, Observatiore de Paris, Durham University and the EU under FP7 Preparatory Fund WP9000 and FP7 OPTICON JRA-1
Current Status (12th September 2011)
CANARY is currently in Phase B AIT. The Phase B upgrades adds a new laser launch system, an upgraded calibration unit and a Laser Guide Star (LGS) WaveFront Sensor (WFS).
The laser launch system is due to be shipped to La Palma at the end of this month for integration on the telescope. The laser launch system combines the light from two 18W pulsed Nd:YAG lasers which is then sent into the existing William Herschel Telescope beam launch telescope. At this point, the combined beam is split into 4 separate LGS beams to create an asterism with a diameter of 30-90" on-sky.
The components for the laser guide star WFS are due to be integrated at LESIA in Paris at the end of October