VISTA (telescope)

VISTA is carrying out surveys of the southern sky at near infrared wavelengths. Such surveys should both return direct scientific results and help select objects for further studies with larger telescopes. There are two related projects: the Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope in Hawaii carries out infrared surveys of the northern sky, and the VLT Survey Telescope in Chile carries out surveys of the southern sky in visible light. summit. ). The project was initiated in 1999 by the VISTA Consortium of 18 universities in the United Kingdom (UK), which obtained funding from a joint infrastructure fund of the UK government and further funding from the Particle Physics and Astronomy Research Council. The project is valued at €46M (£36M). After considering several sites in Chile, the consortium chose the Paranal Observatory of the European Southern Observatory (ESO), namely a secondary peak 1,500 m from the Very Large Telescope (VLT). The consortium selected the UK Astronomy Technology Centre to take technical responsibility for design and construction of the telescope. Two years later – in 2002 – the UK joined ESO, and VISTA became an in-kind component of the joining fee. The consortium then completed the construction and commissioning of the telescope, and the Science and Technology Facilities Council – on behalf of the UK – handed over the telescope to ESO, for the benefit of astronomers in all its member countries. ==VISTA Surveys==

The scientific goals of the VISTA surveys, which started in 2010, include many of the most exciting problems in astrophysics today, ranging from the nature of dark energy to the threat of near-Earth asteroids. More information about each of the VISTA surveys can be found on the ESO — VISTA Surveys website and in the ESO — Public Surveys Projects webpage. ==Science with VISTA==

Because VISTA is a large telescope that also has a large field of view it can both detect faint sources and also cover wide areas of sky quickly. Each VISTA image captures a section of sky covering about ten times the area of the full Moon and it will be able to detect and catalogue objects over the whole southern sky with a sensitivity that is forty times greater than that achieved with earlier infrared sky surveys such as the highly successful Two Micron All-Sky Survey. This jump in observational power—comparable to the step in sensitivity from the unaided eye to Galileo's first telescope—will reveal vast numbers of new objects and allow the creation of far more complete inventories of rare and exotic objects in the southern sky. Infrared measurements from the VVV astronomical survey have been employed to bolster the cosmic distance ladder, namely by providing reliable distances to star clusters and Cepheid variable stars. ==Selection of VISTA Images==

The first released image (left) shows the Flame Nebula (NGC 2024), a spectacular star-forming cloud of gas and dust in the familiar constellation of Orion (the Hunter) and its surroundings. In visible light the core of the object is hidden behind thick clouds of dust, but the VISTA image, taken at infrared wavelengths, can penetrate the murk and reveal the cluster of hot young stars hidden within. The wide field of view of the VISTA camera also captures the glow of NGC 2023 and the ghostly form of the famous Horsehead Nebula. An image of the "Blue Lagoon" is seen on the left (below the Flame Nebula picture) — it is an infrared image taken as part of the VVV survey. It shows the stellar nursery called the Lagoon Nebula (also known as Messier 8), which lies about 4000–5000 light-years away in the constellation of Sagittarius (the Archer). VISTA can also stare far beyond our galaxy. In the example on the left (below the image of the Orion Nebula) the telescope took a family photograph of a cluster of galaxies in the constellation of Fornax (the Chemical Furnace). The wide field allows many galaxies to be captured in a single image including the striking barred-spiral NGC 1365 and the big elliptical galaxy NGC 1399. The image was constructed from images taken through Z, J and Ks filters in the near-infrared part of the spectrum and has captured many of the cluster members in a single image. At the lower-right is the elegant barred-spiral galaxy NGC 1365 and to the left the big elliptical NGC 1399, surrounded by a swarm of faint globular clusters. The image is about 1 degree by 1.5 degrees in extent and the total exposure time was 25 minutes. == Technical details ==

Telescope design ) The objective to repeatedly image large areas of sky at seeing-limited resolution led to a unique optical design. The primary mirror is a concave hyperboloid with 4.1 m diameter and about f/1 focal ratio. The mirror has a meniscus shape of 17 cm thickness with a central 1.2 m hole to accommodate the camera at the Cassegrain focus. It was cast from Zerodur by Schott in Germany and subsequently polished and figured by LZOS, Moscow. It is the largest mirror of this shape and of such short focal ratio; polishing it took 2 years, which was longer than anticipated. The mirror is supported by a number of actuators (81 on the back and 24 around the edge), which allow its shape to be controlled by computers. The secondary mirror is a convex hyperboloid of 1.24 m diameter. The combination of the two hyperbolic mirrors makes this a quasi-Ritchey-Chrétien design. The combined focal ratio is about f/3, but the image quality of the two mirrors alone would be poor. The secondary mirror is mounted on a hexapod support so that its position, tip, and tilt are also computer-controlled. The infrared camera was built by a consortium composed of the Rutherford Appleton Laboratory, the UK Astronomy Technology Centre, and Durham University, and is the world's largest at almost three tonnes. Telescope and camera form a single optical design, as the three field correction lenses in the camera are essential for the projection of a focussed image of the sky on the detectors. For an infrared camera, it is also vital to block heat radiation from the telescope and dome. This is accomplished by a sequence of cooled baffles in front of the field corrector lenses. Also, the secondary mirror is undersized to avoid edge detectors viewing warm structure outside the edge of the primary; this means the aperture seen by any point in the image plane is 3.7 m. This design requires the camera's vacuum cryostat – which cools the detectors as well as the baffles – to be more than 2 m long, with a front window of 95  cm diameter. A filter wheel just in front of the detectors allows the selection of a particular infrared wavelength range. Over an area corresponding to 1.65° diameter on the sky, the image plane has 16 arrays of infrared detectors, Operation and data flow . On completion, the telescope was handed over to ESO, which has selected six public surveys for VISTA, taking up 75% of the available observing time. Proprietary surveys to occupy the remaining time are proposed to ESO, which will schedule approved proposals for observation. The observations are carried out by operators at the Paranal Observatory, remotely from the VLT control building. The combination of the large detector array and the short and frequent exposures necessary at infrared wavelengths results in a high data rate of 200–300 GB per night. A quick-look reduction at the Paranal Observatory will be used for daily quality control, but the principal data flow is to transfer the raw data to ESO headquarters in Garching near Munich, Germany, for ingestion into the data archive. Users can extract paw prints (see above) and pass them through a calibration pipeline to remove instrumental artefacts and calibrate the astrometry and photometry. The archive data will also be copied to the VISTA Data Flow System in the UK, where the paw prints will be combined into tiles (see above) and where source catalogues will be prepared from these. == See also ==