VISTA (telescope)
Encyclopedia
The VISTA is a reflecting telescope
with a 4.1 metre mirror, located at the Paranal Observatory
in Chile
. It is operated by the European Southern Observatory
and saw first light
in December 2009. VISTA is a survey telescope working at infrared wavelengths, and is by far the largest telescope in the world dedicated to surveying the sky at near-infrared wavelengths. The telescope has only one instrument: VIRCAM, the Vista InfraRed CAMera. This is a 3-tonne camera containing 16 special detectors sensitive to infrared light, with a combined total of 67 million pixels.
Observing at wavelengths longer than those visible to the human eye will allow VISTA to study objects that may be almost impossible to see in visible light because they are cool, obscured by dust clouds or because their light has been stretched towards redder wavelengths by the expansion of space during the light’s long journey from the early Universe.
VISTA was conceived and developed by a consortium of universities in the United Kingdom led by Queen Mary, University of London
and became an in-kind contribution to ESO as part of the UK's accession agreement, with the subscription paid by the UK Science and Technology Facilities Council
(STFC).
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.
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 a 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.
There are six large public surveys being conducted by VISTA: UltraVISTA, VIKING: VISTA Kilo-Degree Infrared Galaxy Survey, VMC: VISTA Magellanic Survey, VVV: VISTA Variables in the Via Lactea, VHS: VISTA Hemisphere Survey, VIDEO: VISTA Deep Extragalactic Observations Survey. These will take up the majority of the observing time in the telescope’s first five years of operations. The surveys cover different areas of sky to different depths to attack a wide range of scientific questions. 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.
VISTA observations will support research in many astronomical areas. Within our galaxy, VISTA is expected to find many new brown dwarf stars and be able to test ideas about the nature of dark matter. One VISTA survey is designed to find and study huge numbers of variable stars in our galaxy by taking images of the same areas of sky at different times. Using VISTA data astronomers will be able to map the structure of our galaxy in much more detail than ever before. Another VISTA survey will study our neighbouring small galaxies, the Magellanic Clouds, and their surroundings. VISTA data will also be used to created a 3D map of about 5% of the entire observable Universe. Further out, VISTA will be a powerful tool for discovering remote quasars and studying the evolution of galaxies and clusters of galaxies. It will help to probe the nature of dark energy by finding very distant galaxy clusters.
Other stunning nebula images include the VISTA views of the Orion Nebula
and the Lagoon Nebula
. The picture on the right is a wide-field view of the Orion Nebula (Messier 42), lying about 1350 light-years from Earth, taken with the VISTA infrared survey telescope at ESO’s Paranal Observatory in Chile. The telescope’s huge field of view allows the whole nebula and its surroundings to be imaged in a single picture and its infrared vision also means that it can peer deep into the normally hidden dusty regions and reveal the curious antics of the very active young stars buried there. 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.
-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, each array with 2048x2048 pixels of 20 μm size, corresponding on average to 0.34" on the sky. The focal length of 12.1 m combines with the baffled aperture of 3.7 m to a focal ratio of 3.26. The arrays are separated by 90% of their width in one direction and by just under 50% their width in the other direction. A single exposure therefore corresponds to a patchy "paw print" on the sky. To fill the gaps and obtain a conventional image at least six shifted paw prints have to be combined into a "tile", which then is 1.5° by 1.0°. The image plane of the camera also has wave front
detectors used to control the shape of the primary mirror and the position and tip/tilt of the secondary mirror (active optics
). This compensates for flexure and ensures a focussed image at all altitudes.
The hilltop where VISTA is located was flattened to erect the enclosure building and an auxiliary building. The auxiliary building includes facilities to wash, strip, and coat the primary mirror. The coating can be in aluminium, or normally in protected silver for better infrared performance. The fixed base of the enclosure supports the rotating steel dome. Two sliding doors form the dome slit. Further dome panels can be opened to increase ventilation, and a wind shield can be deployed to close parts of the slit. During the day, the dome is kept at night-time temperature.
, 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.
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
with a 4.1 metre mirror, located at the Paranal Observatory
Paranal Observatory
Paranal Observatory is an astronomical observatory located on Cerro Paranal at 2,635 m altitude and operated by the European Southern Observatory. The Very Large Telescope is the largest telescope on Paranal, actually composed of four separate 8.2 m telescopes...
in Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. It is operated by the European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
and saw first light
First light
In astronomy, first light is the first use of a telescope to take an astronomical image after it has been constructed. This is often not the first viewing using the telescope; optical tests have likely already been performed during daylight to adjust the components...
in December 2009. VISTA is a survey telescope working at infrared wavelengths, and is by far the largest telescope in the world dedicated to surveying the sky at near-infrared wavelengths. The telescope has only one instrument: VIRCAM, the Vista InfraRed CAMera. This is a 3-tonne camera containing 16 special detectors sensitive to infrared light, with a combined total of 67 million pixels.
Observing at wavelengths longer than those visible to the human eye will allow VISTA to study objects that may be almost impossible to see in visible light because they are cool, obscured by dust clouds or because their light has been stretched towards redder wavelengths by the expansion of space during the light’s long journey from the early Universe.
VISTA was conceived and developed by a consortium of universities in the United Kingdom led by Queen Mary, University of London
Queen Mary, University of London
Queen Mary, University of London is a public research university located in London, United Kingdom and a constituent college of the federal University of London...
and became an in-kind contribution to ESO as part of the UK's accession agreement, with the subscription paid by the UK Science and Technology Facilities Council
Science and Technology Facilities Council
The Science and Technology Facilities Council is a UK government body that carries out civil research in science and engineering, and funds UK research in areas including particle physics, nuclear physics, space science and astronomy .-History:It was formed in April 2007 as a merger of the Particle...
(STFC).
The project
VISTA is carrying out surveys of the southern sky at near infraredInfrared astronomy
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers...
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
United Kingdom Infrared Telescope
UKIRT, the United Kingdom Infra-Red Telescope, is a 3.8 metre infrared reflecting telescope, the largest dedicated infrared telescope in the world. It is operated by the Joint Astronomy Centre in Hilo and located on Mauna Kea, Hawai'i as part of Mauna Kea Observatory...
in Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
carries out infrared surveys of the northern sky, and the VLT Survey Telescope
VLT Survey Telescope
The VLT Survey Telescope is the latest telescope to be added to ESO’s Paranal Observatory in the Atacama Desert of northern Chile. It is housed in an enclosure immediately adjacent to the four Very Large Telescope Unit Telescopes on the summit of Cerro Paranal. The VST is a wide-field survey...
in Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
carries out surveys of the southern sky in visible light.
The project was initiated in 1999 by the VISTA Consortium of 18 universities in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
(UK), which obtained funding from a joint infrastructure fund of the UK government and further funding from the Particle Physics and Astronomy Research Council
Particle Physics and Astronomy Research Council
The Particle Physics and Astronomy Research Council was one of a number of Research Councils in the United Kingdom. It directed, coordinated and funded research in particle physics and astronomy for the people of the UK...
. The project is valued at €46M (£36M).
After considering several sites in Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, the consortium chose the Paranal Observatory
Paranal Observatory
Paranal Observatory is an astronomical observatory located on Cerro Paranal at 2,635 m altitude and operated by the European Southern Observatory. The Very Large Telescope is the largest telescope on Paranal, actually composed of four separate 8.2 m telescopes...
of the European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
(ESO), namely a secondary peak 1,500 m from the Very Large Telescope
Very Large Telescope
The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
(VLT). The consortium selected the UK Astronomy Technology Centre
UK Astronomy Technology Centre
The UK Astronomy Technology Centre is based at the Royal Observatory in Edinburgh, Scotland, and is part of the Science and Technology Facilities Council....
to take technical responsibility for design and construction of the telescope. Two years later – in 2002 – the UK joined ESO, and VISTA became a in-kind
Payment in kind
Payment in kind refers to payment for goods or services with a medium other than legal tender ....
component of the joining fee. The consortium then completed the construction and commissioning of the telescope, and the Science and Technology Facilities Council
Science and Technology Facilities Council
The Science and Technology Facilities Council is a UK government body that carries out civil research in science and engineering, and funds UK research in areas including particle physics, nuclear physics, space science and astronomy .-History:It was formed in April 2007 as a merger of the Particle...
– 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.There are six large public surveys being conducted by VISTA: UltraVISTA, VIKING: VISTA Kilo-Degree Infrared Galaxy Survey, VMC: VISTA Magellanic Survey, VVV: VISTA Variables in the Via Lactea, VHS: VISTA Hemisphere Survey, VIDEO: VISTA Deep Extragalactic Observations Survey. These will take up the majority of the observing time in the telescope’s first five years of operations. The surveys cover different areas of sky to different depths to attack a wide range of scientific questions. 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.VISTA observations will support research in many astronomical areas. Within our galaxy, VISTA is expected to find many new brown dwarf stars and be able to test ideas about the nature of dark matter. One VISTA survey is designed to find and study huge numbers of variable stars in our galaxy by taking images of the same areas of sky at different times. Using VISTA data astronomers will be able to map the structure of our galaxy in much more detail than ever before. Another VISTA survey will study our neighbouring small galaxies, the Magellanic Clouds, and their surroundings. VISTA data will also be used to created a 3D map of about 5% of the entire observable Universe. Further out, VISTA will be a powerful tool for discovering remote quasars and studying the evolution of galaxies and clusters of galaxies. It will help to probe the nature of dark energy by finding very distant galaxy clusters.
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.Other stunning nebula images include the VISTA views of the Orion Nebula
Orion Nebula
The Orion Nebula is a diffuse nebula situated south of Orion's Belt. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. M42 is located at a distance of and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light...
and the Lagoon Nebula
Lagoon Nebula
The Lagoon Nebula is a giant interstellar cloud in the constellation Sagittarius. It is classified as an emission nebula and as an H II region....
. The picture on the right is a wide-field view of the Orion Nebula (Messier 42), lying about 1350 light-years from Earth, taken with the VISTA infrared survey telescope at ESO’s Paranal Observatory in Chile. The telescope’s huge field of view allows the whole nebula and its surroundings to be imaged in a single picture and its infrared vision also means that it can peer deep into the normally hidden dusty regions and reveal the curious antics of the very active young stars buried there. 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.
Telescope Design
The objective to repeatedly image large areas of sky at seeingAstronomical seeing
Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...
-limited resolution led to a unique optical design. The primary mirror is a concave
Curved mirror
A curved mirror is a mirror with a curved reflective surface, which may be either convex or concave . Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices...
hyperboloid with 4.1 m diameter and about f/1 focal ratio. The mirror has a meniscus
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
shape of 17 cm thickness with a central 1.2 m hole to accommodate the camera at the Cassegrain
Cassegrain reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas....
focus. It was cast from Zerodur
Zerodur
Zerodur®, a registered trademark of Schott Glass Technologies, is a lithium aluminosilicate glass-ceramic produced by Schott AG since 1968. It has been used for a number of very large telescope mirrors including Keck I and Keck II. With its very low coefficient of expansion it can be used to...
by Schott in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and subsequently polished and figured
Figuring
Figuring is the process of final polishing of an optical surface to remove imperfections or modify the surface curvature to achieve the shape required for a given application.-Types of figuring:...
by LZOS, Moscow
Moscow
Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...
. 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
Pneumatic actuator
A pneumatic actuator converts energy into motion. The motion can be rotary or linear, depending on the type of actuator.Some types of pneumatic actuators include:*Tie rod cylinders*Rotary actuators*Grippers...
(81 on the back and 24 around the edge), which allow its shape to be controlled by computers.
The secondary mirror is a convex
Curved mirror
A curved mirror is a mirror with a curved reflective surface, which may be either convex or concave . Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices...
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
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...
are also computer-controlled.
The infrared camera was built by a consortium composed of the Rutherford Appleton Laboratory
Rutherford Appleton Laboratory
The Rutherford Appleton Laboratory is one of the national scientific research laboratories in the UK operated by the Science and Technology Facilities Council . It is located on the Harwell Science and Innovation Campus at Chilton near Didcot in Oxfordshire, United Kingdom...
, the UK Astronomy Technology Centre
UK Astronomy Technology Centre
The UK Astronomy Technology Centre is based at the Royal Observatory in Edinburgh, Scotland, and is part of the Science and Technology Facilities Council....
, and Durham University
Durham University
The University of Durham, commonly known as Durham University, is a university in Durham, England. It was founded by Act of Parliament in 1832 and granted a Royal Charter in 1837...
, 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
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
seen by any point in the image plane is 3.7 m. This design requires the camera's vacuum cryostat
Cryostat
A cryostat is a device used to maintain cold cryogenic temperatures. Low temperatures may be maintained within a cryostat by using various refrigeration methods, most commonly using cryogenic fluid bath such as liquid helium. Hence it is usually assembled into a vessel, similar in construction...
– 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, each array with 2048x2048 pixels of 20 μm size, corresponding on average to 0.34" on the sky. The focal length of 12.1 m combines with the baffled aperture of 3.7 m to a focal ratio of 3.26. The arrays are separated by 90% of their width in one direction and by just under 50% their width in the other direction. A single exposure therefore corresponds to a patchy "paw print" on the sky. To fill the gaps and obtain a conventional image at least six shifted paw prints have to be combined into a "tile", which then is 1.5° by 1.0°. The image plane of the camera also has wave front
Wavefront
In physics, a wavefront is the locus of points having the same phase. Since infrared, optical, x-ray and gamma-ray frequencies are so high, the temporal component of electromagnetic waves is usually ignored at these wavelengths, and it is only the phase of the spatial oscillation that is described...
detectors used to control the shape of the primary mirror and the position and tip/tilt of the secondary mirror (active optics
Active optics
Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, mechanical stress...
). This compensates for flexure and ensures a focussed image at all altitudes.
The hilltop where VISTA is located was flattened to erect the enclosure building and an auxiliary building. The auxiliary building includes facilities to wash, strip, and coat the primary mirror. The coating can be in aluminium, or normally in protected silver for better infrared performance. The fixed base of the enclosure supports the rotating steel dome. Two sliding doors form the dome slit. Further dome panels can be opened to increase ventilation, and a wind shield can be deployed to close parts of the slit. During the day, the dome is kept at night-time temperature.
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 ObservatoryParanal Observatory
Paranal Observatory is an astronomical observatory located on Cerro Paranal at 2,635 m altitude and operated by the European Southern Observatory. The Very Large Telescope is the largest telescope on Paranal, actually composed of four separate 8.2 m telescopes...
, remotely from the VLT
Very Large Telescope
The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
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
Garching bei München
Garching bei München or Garching is a city in Bavaria, Germany near Munich. It is the home of several research institutes and university departments. It became a city on 14 September 1990.-Location:...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, 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
- List of largest infrared telescopes
- VLT Survey TelescopeVLT Survey TelescopeThe VLT Survey Telescope is the latest telescope to be added to ESO’s Paranal Observatory in the Atacama Desert of northern Chile. It is housed in an enclosure immediately adjacent to the four Very Large Telescope Unit Telescopes on the summit of Cerro Paranal. The VST is a wide-field survey...
- Very Large TelescopeVery Large TelescopeThe Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...
- European Southern ObservatoryEuropean Southern ObservatoryThe European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
Further reading
- "The ESO survey telescopes". European Southern ObservatoryEuropean Southern ObservatoryThe European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
. Retrieved 23 September 2009. - "VISTA - Visible and Infrared Survey Telescope for Astronomy". European Southern ObservatoryEuropean Southern ObservatoryThe European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
. Retrieved 23 September 2009. - "VISTA: Pioneering new survey telescope starts work". ESO Press Release 49/09, 11 December 2009. Retrieved 11 December 2009. Includes a number of pictures of or taken by the telescope.
External links
- VISTA web site
- VISTA pages at the UK Astronomy Technology CentreUK Astronomy Technology CentreThe UK Astronomy Technology Centre is based at the Royal Observatory in Edinburgh, Scotland, and is part of the Science and Technology Facilities Council....