CHOUGH:The CANARY-Hosted Upgrade for High-Order Adaptive Optics;

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Astronomical Adaptive Optics is used to remove some of the effects of the Earth's atmosphere from observations of the sky made with optical telescopes. An example is the twinkling of the stars. Without AO, the sharpness and brightness of ground-based images is severely degraded with respect to what could be achieved by a telescope in space. The next generation of extremely large telescopes will have diameters of over 30m, compared with 8m today. They will not be able to go into space, so they basically require adaptive optics technology in order to fulfil their scientific missions.Up to now the UK has concentrated, via a key collaboration with France, on the adaptive optics technologies required to correct the images from these large telescopes over a wide range of the sky. This is important, for example, because it will enable many of the earliest and most distant galaxies to be surveyed simultaneously, so their formation can be compared with models, instead of individually. With one night of observing costing over £50000, AO will also ultimately save money as well as time and improve the quality of the data measured.Instead of moderate quality correction for many targets, we can instead concentrate on a very high degree of correction for one target in order to maximize the quality of the AO-enhanced images. This is called High-Order Adaptive Optics and enables us to study small, bright objects such as stars and their shape and current state. More excitingly, it will also let us look at the regions of space close to these stars where we can see if they have faint companions such as failed stars or brown dwarfs. Even more excitingly, these circumstellar regions can hold discs of dust and gas from which planets form so we need AO to better understand this aspect of astrophysics. HOAO is very difficult because we must apply AO correction both more finely and more quickly than is currently done which is why we focus on only one target.This project will enable to the UK to participate much more fully in this area of HOAO. It will do so by allowing us to re-use an existing experiment, CANARY, by extending it with a very high resolution deformable mirror, which corrects the starlight, and new measurement cameras to drive this mirror. The mirror is already in our possession, so this project is a low-cost but high-results experiment that will prove this novel type of AO using the William Herschel Telescope on La Palma, Canary Islands. Our project is called CHOUGH, or the Canary High Order UpGrade for High-order adaptive optics and its name comes from a type of crow commonly found on La Palma. The WHT telescope is particularly important as it has a purpose built laboratory to support the testing of new ideas such as CHOUGH, and this means it is possible to show that the ideas in CHOUGH work in real-life, which we call "on sky", instead of just in computer simulations.