Survey telescope nears completion

A 4.1 metre diameter primary mirror, a vital part of the world's newest and fastest survey telescope, VISTA [the Visible and Infrared Survey Telescope for Astronomy] has been delivered to its new mountain top home at Cerro Paranal Observatory, Chile. The mirror will now be installed on the telescope and coupled with a small test camera for initial testing prior to installing the main camera in June. Full scientific operations are due to start early next year. VISTA, a survey telescope being constructed for ESO (the Organisation for Astronomical Research in the Southern Hemisphere), will form part of ESO's Very Large Telescope (VLT) facility. It is an in-kind contribution to ESO as part of the UK's accession agreement, with the subscription paid by the Science and Technology Facilities Council (STFC).

The mirror arrived over the Easter weekend at the Cerro Paranal Observatory where the telescope is being assembled at an altitude of 2518m, in Chile's Atacama Desert.

VISTA Project Manager Alistair McPherson from STFC's UK Astronomy Technology Centre (UK ATC) travelled to Moscow to accompany the mirror on its journey to Chile. "Constructing modern telescopes brings together expertise from all over the world - such as a specialist mirror from Russia, for a British led telescope, project-managed from Edinburgh to be assembled in Chile! This has been a major milestone for VISTA. The precious mirror was loaded on to a plane in a special cradle that used tennis balls to cushion it from impact for its arduous journey across three continents."

Dr Will Sutherland of Queen Mary, University of London and Project Scientist on VISTA said, "The mirror had a difficult four-day journey, by air and by road, from Moscow, where it had been polished. It arrived in perfect condition and now that it has been coated, we will install the mirror in the telescope with a small test camera for about four weeks testing. We plan to install the main camera in June."

The VISTA 4.1 metre diameter primary mirror is the most strongly curved large mirror ever polished to such a precise and exacting surface accuracy - deviations from a perfect surface of less than 1/3000th of the thickness of a human hair. On arrival at Cerro Paranal it was safely craned into the telescope dome where it was washed and coated with a thin layer of protected silver in the facility's coating plant. Silver is the best metal for the purpose since it reflects over 98% of near-infrared light, better than the more commonly used aluminium. To date, the reflectivity produced by the silver coating- a relatively new venture - is well above that specified and exceeds all other telescopes.

VISTA will survey large areas of the southern sky at near infrared wavelengths (2 to 4 times the wavelength of visible light) to study objects that are not seen easily in optical light either because they are too cool (such as brown dwarfs), or are surrounded by interstellar dust which infrared light penetrates much better than optical, or whose optical light is redshifted into the near infrared by the expansion of the Universe. Amongst other things VISTA's surveys will help our understanding of the nature and distribution and origin of known types of stars and galaxies, map the 3-D structure of our galaxy, and help determine the relation between the 3-D structure of the universe and the mysterious 'dark energy' and dark matter'. Samples of objects will be followed up in detail with further observations by other telescopes and instruments such as the nearby Very Large Telescope (VLT).

Professor Richard Wade, STFC Chief Operating Officer and President of ESO Council said "The delivery of the last component of VISTA is a significant milestone and we are delighted with the progress made since the mirror arrived. Now astronomers can really look forward to being able to perform unparalleled observing of our Southern skies."


Images

Uncoated Mirror

Primary Mirror after being washed and prior to placement into the coating plant to recieve a protected silver coating on 03 April 2008. Credit: VISTA (Andy Born)

 

Coated Mirror

Primary Mirror in the Mirror cell after being coated in 3-layer protected silver (NiCr-Ag-Nicr) on 04 April 2008. The secondary mirror support structure is not yet refitted. Credit: VISTA (Andy Born)

 

Further Images are available at the VISTA webiste.


Contacts

Natalie Bealing, Science and Technology Facilities Council Press Office
n.d.bealing@stfc.ac.uk
01235 445484

Will Sutherland, Project Scientist, Queen Mary, University of London
w.j.sutherland@qmul.ac.uk
07889 396 348

Sian Halkyard, Press Officer Queen Mary, University of London
s.halkyard@qmul.ac.uk
020 7882 7454

Henri Boffin, European Southern Observatory Press Office
hboffin@eso.org
+49 89 32006 222


Notes to Editors

VISTA Consortium

VISTA is a £36 million project, funded by grants from the DTI's Joint Infrastructure Fund and the STFC to Queen Mary, University of London, the lead institute of the VISTA consortium. VISTA is project managed by STFC's UK Astronomy Technology Centre.

The VISTA consortium consists of: Queen Mary University of London, Queen's University of Belfast, University of Birmingham, University of Cambridge, Cardiff University, University of Central Lancashire, University of Durham, The University of Edinburgh, University of Hertfordshire, Keele University, Leicester University, Liverpool John Moores University, University of Nottingham, University of Oxford, University of St Andrews, University of Southampton, University of Sussex, University College London. The delivery of VISTA is an in-kind payment as part of UK's contribution to ESO.

VISTA Telescope

The VISTA telescope will have an extremely large field of view covering an area of the sky ten times the area of the moon in a single image. This makes it ideal for mapping large areas of the sky. Being a dedicated survey telescope, the optical design has been optimised for this purpose. The focusing power of the telescope is in the two mirrors, and three smaller lenses are used to give sharp images over the wide field of view. When it is completed it will be the world's largest telescope dedicated to ground based survey work. Initially it will be equipped with the world's largest infrared camera, and later may be augmented with an optical camera. The delivery of VISTA is an in-kind payment as part of UK's contribution to ESO.

VISTA Science

VISTA is designed to be capable of making wide-field imaging observations from optical wavelengths out to 2.5 micrometres, thereby supporting a huge variety of existing projects from Solar System studies to cosmology:

VISTA Telescope Facility

The Enclosure is a 19 metre diameter building which is designed to protect the telescope from the environment. The environmental management system maintains the internal atmosphere at the predicted night-time temperature to stop unwanted warm air currents causing blurring of the images. In addition, at night, the enclosure rotates in harmony with the telescope and includes a moon screen to stop moonlight impinging on the primary mirror and a wind screen and ventilation doors to control air flow throughout the observing night.

VISTA primary mirror

The VISTA primary mirror is 4.1 metres in diameter, with a 1.2 metre central hole for the camera; it is 17 centimetres thick and weighs nearly 5.5 tonnes. It is made of a special ultra-low expansion glass-ceramic called Zerodur, from Schott Glas in Germany, and has been polished to the precise shape (a hyperboloid) by LZOS in Moscow; this polishing process has taken nearly two years.