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65-647: With its 4-meter class primary mirror, the Lowell Discovery Telescope is the fifth largest telescope in the continental United States (as of 2019). Final construction of the telescope was completed by February 2012 and first light images were taken in April 2012. The LDT uses a Ritchey–Chrétien design with an f/1.9 primary mirror. The 6700-pound primary mirror measures 4.3 m (170 in) in diameter yet only about 10 cm (3.9 in) in thickness. This finely figured, thin meniscus mirror, held in shape by

130-459: A primary mirror that measures 8.2 meters in diameter. These optical telescopes , named Antu , Kueyen , Melipal , and Yepun (all words for astronomical objects in the Mapuche language ), are generally used separately but can be combined to achieve a very high angular resolution . The VLT array is also complemented by four movable Auxiliary Telescopes (ATs) with 1.8-meter apertures. The VLT

195-463: A surface brightness high enough to be observed in the mid-infrared, and objects must be at several thousands of degrees Celsius for near-infrared observations using the VLTI. This includes most of the stars in the solar neighborhood and many extragalactic objects such as bright active galactic nuclei , but this sensitivity limit rules out interferometric observations of most solar-system objects. Although

260-518: A 1.1 metre lightweight beryllium secondary mirror. A flat tertiary mirror diverts the light to one of two instruments at the f/15 Nasmyth foci on either side, with a system focal length of 120 m, or the tertiary tilts aside to allow light through the primary mirror central hole to a third instrument at the Cassegrain focus. This allows switching between any of the three instruments within 5 minutes, to match observing conditions. Additional mirrors can send

325-706: A 102 cm (40 in) instrument constructed by Ritchey for the United States Naval Observatory ; that telescope is still in operation at the Naval Observatory Flagstaff Station . As with the other Cassegrain-configuration reflectors, the Ritchey–Chrétien telescope (RCT) has a very short optical tube assembly and compact design for a given focal length . The RCT offers good off-axis optical performance, but its mirrors require sophisticated techniques to manufacture and test. Hence

390-566: A 156-element active optics system, regularly delivers sub-arcsecond seeing. The mirror was ground and polished into its hyperbolic shape at the Optical Engineering and Fabrication Facility of the University of Arizona College of Optical Sciences (in Tucson, Arizona ). The telescope is one of the most powerful in the world, thanks to a unique housing that can accommodate up to five instruments at

455-634: A Ritchey–Chrétien system, the conic constants K 1 {\displaystyle K_{1}} and K 2 {\displaystyle K_{2}} of the two mirrors are chosen so as to eliminate third-order spherical aberration and coma; the solution is: and Note that K 1 {\displaystyle K_{1}} and K 2 {\displaystyle K_{2}} are less than − 1 {\displaystyle -1} (since M > 1 {\displaystyle M>1} ), so both mirrors are hyperbolic. (The primary mirror

520-568: A broken pump in a giant washing machine and resolving a rigging issue. The procedure is part of routine scheduled maintenance. The area surrounding the Very Large Telescope was featured in the 2008 film Quantum of Solace . The ESO Hotel , the Residencia, served as a backdrop for part of the James Bond movie. Producer Michael G. Wilson said: "The Residencia of Paranal Observatory caught

585-520: A large set of instruments permitting observations to be performed from the near-ultraviolet to the mid-infrared (i.e. a large fraction of the light wavelengths accessible from the surface of the Earth ), with the full range of techniques including high-resolution spectroscopy, multi-object spectroscopy , imaging, and high-resolution imaging. In particular, the VLT has several adaptive optics systems, which correct for

650-411: A larger usable field of view compared to the parabolic designs actually used. However, Ritchey and Hale had a falling-out. With the 100-inch project already late and over budget, Hale refused to adopt the new design, with its hard-to-test curvatures, and Ritchey left the project. Both projects were then built with traditional optics. Since then, advances in optical measurement and fabrication have allowed

715-547: A small optical device called a null corrector that makes the hyperbolic primary look spherical for the interferometric test. On the Hubble Space Telescope , this device was built incorrectly (a reflection from an un-intended surface leading to an incorrect measurement of lens position) leading to the error in the Hubble primary mirror. Incorrect null correctors have led to other mirror fabrication errors as well, such as in

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780-518: Is a specialized variant of the Cassegrain telescope that has a hyperbolic primary mirror and a hyperbolic secondary mirror designed to eliminate off-axis optical errors ( coma ). The RCT has a wider field of view free of optical errors compared to a more traditional reflecting telescope configuration. Since the mid 20th century, a majority of large professional research telescopes have been Ritchey–Chrétien configurations; some well-known examples are

845-408: Is capable of observing both visible and infrared wavelengths . Each individual telescope can detect objects that are roughly four billion times fainter than what can be seen with the naked eye . When all the telescopes are combined, the facility can achieve an angular resolution of approximately 0.002 arcsecond. In single telescope mode, the angular resolution is about 0.05 arcseconds. The VLT

910-466: Is done using 1.8 meter Auxiliary Telescopes (ATs), which are dedicated to full-time interferometric measurements. The first observations using a pair of ATs were conducted in February 2005, and all the four ATs have now been commissioned. For interferometric observations on the brightest objects, there is little benefit in using 8 meter telescopes rather than 1.8 meter telescopes. The first two instruments at

975-447: Is introduced, the limiting magnitude of the VLTI is expected to improve by a factor of almost 1000, reaching a magnitude of about 14. This is similar to what is expected for other fringe tracking interferometers. In spectroscopic mode, the VLTI can currently reach a magnitude of 1.5. The VLTI can work in a fully integrated way, so that interferometric observations are actually quite simple to prepare and execute. The VLTI has become worldwide

1040-481: Is one of the most productive facilities for astronomy, second only to the Hubble Space Telescope in terms of the number of scientific papers produced from facilities operating at visible wavelengths. Some of the pioneering observations made using the VLT include the first direct image of an exoplanet , the tracking of stars orbiting around the supermassive black hole at the centre of the Milky Way , and observations of

1105-560: Is the gravitational redshift . In fact, the observation has been conducted for over 26 years with the SINFONI and NACO adaptive optics instruments in the VLT while the new approach in 2018 also used the beam-combiner instrument GRAVITY. The Galactic Centre team at the Max Planck Institute for Extraterrestrial Physics (MPE) used these observations to reveal these effects for the first time. Other discoveries with VLT's signature include

1170-564: Is the capital to write about the implications of these names. It drew many entries dealing with the cultural heritage of ESO's host country. The winning essay was submitted by 17-year-old Jorssy Albanez Castilla from Chuquicamata near the city of Calama . She received the prize, an amateur telescope, during the inauguration of the Paranal site. Unit Telescopes 1–4 are since known as Antu (Sun), Kueyen (Moon), Melipal ( Southern Cross ), and Yepun (Evening Star), respectively. Originally there

1235-460: Is typically quite close to being parabolic, however.) The hyperbolic curvatures are difficult to test, especially with equipment typically available to amateur telescope makers or laboratory-scale fabricators; thus, older telescope layouts predominate in these applications. However, professional optics fabricators and large research groups test their mirrors with interferometers . A Ritchey–Chrétien then requires minimal additional equipment, typically

1300-610: The GRAVITY instrument on their Very Large Telescope Interferometer (VLTI), announced the first direct detection of an exoplanet , HR 8799 e , using optical interferometry . One of the large mirrors of the telescopes was the subject of an episode of the National Geographic Channel 's reality series World's Toughest Fixes , where a crew of engineers removed and transported the mirror to be cleaned and re-coated with aluminium . The job required battling strong winds, fixing

1365-512: The Hubble Space Telescope , the Keck telescopes and the ESO Very Large Telescope . The Ritchey–Chrétien telescope was invented in the early 1910s by American astronomer George Willis Ritchey and French astronomer Henri Chrétien . Ritchey constructed the first successful RCT, which had an aperture diameter of 60 cm (24 in) in 1927 (Ritchey 24-inch reflector). The second RCT was

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1430-550: The New Technology Telescope . In practice, each of these designs may also include any number of flat fold mirrors , used to bend the optical path into more convenient configurations. This article only discusses the mirrors required for forming an image, not those for placing it in a convenient location. Ritchey intended the 100-inch Mount Wilson Hooker telescope (1917) and the 200-inch (5 m) Hale Telescope to be RCTs. His designs would have provided sharper images over

1495-664: The RCT design to take over – the Hale telescope, dedicated in 1948, turned out to be the last world-leading telescope to have a parabolic primary mirror. Very Large Telescope The Very Large Telescope ( VLT ) is an astronomical facility operated since 1998 by the European Southern Observatory , located on Cerro Paranal in the Atacama Desert of northern Chile . It consists of four individual telescopes, each equipped with

1560-535: The Ritchey-Chrétien focus. The LDT can switch between any of these instruments in about a minute, making it uniquely suited for time-domain programs as well as opportunity targets such as gamma ray bursts and supernovae. Lowell Observatory and Discovery Communications formed a partnership to build the Discovery Channel Telescope in February 2003. A special-use permit for construction and operation of

1625-533: The Ritchey–Chrétien configuration is most commonly found on high-performance professional telescopes. A telescope with only one curved mirror, such as a Newtonian telescope , will always have aberrations. If the mirror is spherical, it will suffer primarily from spherical aberration . If the mirror is made parabolic, to correct the spherical aberration, then it still suffers from coma and astigmatism , since there are no additional design parameters one can vary to eliminate them. With two non-spherical mirrors, such as

1690-504: The Ritchey–Chrétien telescope, coma can be eliminated as well, by making the two mirrors' contribution to total coma cancel. This allows a larger useful field of view. However, such designs still suffer from astigmatism. The basic Ritchey–Chrétien two-surface design is free of third-order coma and spherical aberration . However, the two-surface design does suffer from fifth-order coma, severe large-angle astigmatism , and comparatively severe field curvature . When focused midway between

1755-509: The Schmidt requires a full-aperture corrector plate, which restricts it to apertures below 1.2 meters, while a Ritchey–Chrétien can be much larger. Other telescope designs with front-correcting elements are not limited by the practical problems of making a multiply-curved Schmidt corrector plate, such as the Lurie–Houghton design . In a Ritchey–Chrétien design, as in most Cassegrain systems,

1820-515: The UTs are 8.2 meters in diameter but, in practice, the pupil of the telescopes is defined by their secondary mirrors, effectively reducing the usable diameter to 8.0 meters at the Nasmyth focus and 8.1 meters at the Cassegrain focus . The 8.2 m-diameter telescopes are housed in compact, thermally controlled buildings, which rotate synchronously with the telescopes. This design minimises any adverse effects on

1885-570: The UTs started operating in May 1998 and was offered to the astronomical community on 1 April 1999. The other telescopes became operational in 1999 and 2000, enabling multi-telescope VLT capability. Four 1.8-metre Auxiliary Telescopes (ATs) have been added to the VLTI to make it available when the UTs are being used for other projects. These ATs were installed and became operational between 2004 and 2007. The VLT's 8.2-meter telescopes were originally designed to operate in three modes: The UTs are equipped with

1950-418: The VLTI lab, along with ESPRESSO fed via fibre-optics (not interferometric). From 2014 to 2020 it underwent a major upgrade to CRIRES+ to provide ten times larger simultaneous wavelength coverage. A new detector focal plane array of three Hawaii 2RG detectors with a 5.3 μm cut-off wavelength replaced the existing detectors, a new spectropolarimetric unit is added, and the calibration system is enhanced. One of

2015-486: The VLTI were VINCI (a test instrument used to set up the system, now decommissioned) and MIDI, which only allow two telescopes to be used at any one time. With the installation of the three-telescope AMBER closure-phase instrument in 2005, the first imaging observations from the VLTI are expected soon. Deployment of the Phase Referenced Imaging and Microarcsecond Astrometry (PRIMA) instrument started 2008 with

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2080-441: The afterglow of the furthest known gamma-ray burst . The VLT consists of an arrangement of four large (8.2 metre diameter) telescopes (called Unit Telescopes or UTs) with optical elements that can combine them into an astronomical interferometer (VLTI), which is used to resolve small objects. The interferometer also includes a set of four 1.8 meter diameter movable telescopes dedicated to interferometric observations. The first of

2145-560: The aim to allow phase-referenced measurements in either an astrometric two-beam mode or as a fringe-tracker successor to VINCI, operated concurrent with one of the other instruments. After falling drastically behind schedule and failing to meet some specifications, in December 2004 the VLT Interferometer became the target of a second ESO "recovery plan". This involves additional effort concentrated on improvements to fringe tracking and

2210-643: The angular diameters of four red dwarfs including Proxima Centauri . During this operation it achieved an angular resolution of ±0.08 milli-arc-seconds (0.388 nano-radians). This is comparable to the resolution achieved using other arrays such as the Navy Prototype Optical Interferometer and the CHARA array . Unlike many earlier optical and infrared interferometers, the Astronomical Multi-Beam Recombiner (AMBER) instrument on VLTI

2275-537: The detection of carbon monoxide molecules in a galaxy located almost 11 billion light-years away for the first time, a feat that had remained elusive for 25 years. This has allowed astronomers to obtain the most precise measurement of the cosmic temperature at such a remote epoch. Another important study was that of the violent flares from the supermassive black hole at the centre of the Milky Way. The VLT and APEX teamed up to reveal material being stretched out as it orbits in

2340-412: The effects of atmospheric turbulence, providing images almost as sharp as if the telescope were in space. In the near-infrared, the adaptive optics images of the VLT are up to three times sharper than those of the Hubble Space Telescope , and the spectroscopic resolution is many times better than Hubble. The VLTs are noted for their high level of observing efficiency and automation. The primary mirrors of

2405-462: The enclosure and transporter are mechanically isolated from the telescope, to ensure that no vibrations compromise the data collected. The transporter section runs on tracks, so the ATs can be moved to 30 different observing locations. As the VLTI acts rather like a single telescope as large as the group of telescopes combined, changing the positions of the ATs means that the VLTI can be adjusted according to

2470-407: The exoplanetary atmosphere . This important wavelength region is covered by CRIRES+, which will additionally allow tracking multiple absorption lines simultaneously. In its interferometric operating mode, the light from the telescopes is reflected off mirrors and directed through tunnels to a central beam combining laboratory. In the year 2001, during commissioning, the VLTI successfully measured

2535-430: The first extrasolar planet so imaged, tracking individual stars moving around the supermassive black hole at the centre of the Milky Way, and observing the afterglow of the furthest known gamma-ray burst . In 2018, the VLT helped to perform the first successful test of Albert Einstein 's General Relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole, that

2600-462: The first general user optical/infrared interferometric facility offered with this kind of service to the astronomical community. Because of the many mirrors involved in the optical train, about 95% of the light is lost before reaching the instruments at a wavelength of 1 μm, 90% at 2 μm and 75% at 10 μm. This refers to reflection off 32 surfaces including the Coudé train, the star separator,

2665-432: The first time using the VLT. The planet, which is known as GJ 1214b , was studied as it passed in front of its parent star and some of the starlight passed through the planet's atmosphere. In all, of the top 10 discoveries done at ESO's observatories, seven made use of the VLT. Each Unit Telescope is a Ritchey-Chretien Cassegrain telescope with a 22-tonne 8.2 metre Zerodur primary mirror of 14.4 m focal length, and

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2730-473: The four VLT Unit Telescopes, to replace the original technical designations of UT1 to UT4. In March 1999, at the time of the Paranal inauguration, four meaningful names of objects in the sky in the Mapuche language were chosen. This indigenous people lives mostly south of Santiago de Chile. An essay contest was arranged in this connection among schoolchildren of the Chilean II Region of which Antofagasta

2795-519: The four smaller 1.8-metre ATs are available and dedicated to interferometry to allow the VLTI to operate every night. The top part of each AT is a round enclosure, made from two sets of three segments, which open and close. Its job is to protect the delicate 1.8-metre telescope from the desert conditions. The enclosure is supported by the boxy transporter section, which also contains electronics cabinets, liquid cooling systems, air-conditioning units, power supplies, and more. During astronomical observations

2860-453: The individual telescopes. The light beams are combined in the VLTI using a complex system of mirrors in tunnels where the light paths must be kept equal within differences of less than 1 μm over a light path of a hundred metres. With this kind of precision, the VLTI can reconstruct images with an angular resolution of milliarcseconds. It had long been ESO's intention to provide "real" names to

2925-504: The inner structure of the mysterious Eta Carinae . In March 2011, the PIONIER instrument for the first time simultaneously combined the light of the four Unit Telescopes, potentially making VLTI the biggest optical telescope in the world. However, this attempt was not really a success. The first successful attempt was in February 2012, with four telescopes combined into a 130-meter diameter mirror. In March 2019, ESO astronomers, employing

2990-507: The intense gravity close to the central black hole. Using the VLT, astronomers have also estimated the age of extremely old stars in the NGC 6397 cluster. Based on stellar evolution models, two stars were found to be 13.4 ± 0.8 billion years old, that is, they are from the earliest era of star formation in the Universe. They have also analysed the atmosphere around a super-Earth exoplanet for

3055-400: The light via tunnels to the central VLTI beam-combiners. The maximum field-of-view (at Nasmyth foci) is around 27 arcminutes diameter, slightly smaller than the full moon, though most instruments view a narrower field. Each telescope has an alt-azimuth mount with total mass around 350 tonnes, and uses active optics with 150 supports on the back of the primary mirror to control the shape of

3120-418: The main delay line, beam compressor and feeding optics. Additionally, the interferometric technique is such that it is very efficient only for objects that are small enough that all their light is concentrated. For instance, an object with a relatively low surface brightness such as the moon cannot be observed, because its light is too diluted. Only targets which are at temperatures of more than 1,000° C have

3185-496: The mirror, which weighs about 3,000 kg (6,700 lb), was completed by the University of Arizona 's College of Optical Sciences. This process took about three years. The mirror was delivered to the site in June 2010, subsequently aluminized, and mounted on the telescope in August 2011. The telescope saw first light in 2012 and it was fully operational that year. The telescope's mirror

3250-477: The needs of the observing project. The reconfigurable nature of the VLTI is similar to that of the Very Large Array . Results from the VLT have led to the publication of an average of more than one peer-reviewed scientific paper per day. For instance in 2017, over 600 refereed scientific papers were published based on VLT data. The telescope's scientific discoveries include direct imaging of Beta Pictoris b ,

3315-504: The observing conditions, for instance from air turbulence in the telescope tube, which might otherwise occur due to variations in the temperature and wind flow. The principal role of the main VLT telescopes is to operate as four independent telescopes. The interferometry (combining light from multiple telescopes) is used about 20 percent of the time for very high-resolution on bright objects, for example, on Betelgeuse . This mode allows astronomers to see details up to 25 times finer than with

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3380-416: The performance of the main delay lines . Note that this only applies to the interferometer and not other instruments on Paranal. In 2005, the VLTI was routinely producing observations, although with a brighter limiting magnitude and poorer observing efficiency than expected. As of March 2008 , the VLTI had already led to the publication of 89 peer-reviewed publications and had published a first-ever image of

3445-711: The primary and secondary mirrors, respectively, in a two-mirror Cassegrain configuration are: and where If, instead of B {\displaystyle B} and D {\displaystyle D} , the known quantities are the focal length of the primary mirror, f 1 {\displaystyle f_{1}} , and the distance to the focus behind the primary mirror, b {\displaystyle b} , then D = f 1 ( F − b ) / ( F + f 1 ) {\displaystyle D=f_{1}(F-b)/(F+f_{1})} and B = D + b {\displaystyle B=D+b} . For

3510-498: The result is a three-mirror anastigmat . Alternatively, a RCT may use one or several low-power lenses in front of the focal plane as a field-corrector to correct astigmatism and flatten the focal surface, as for example the SDSS telescope and the VISTA telescope ; this can allow a field-of-view up to around 3° diameter. The Schmidt camera can deliver even wider fields up to about 7°. However,

3575-407: The sagittal and tangential focusing planes, stars appear as circles, making the Ritchey–Chrétien well suited for wide field and photographic observations. The remaining aberrations of the two-element basic design may be improved with the addition of smaller optical elements near the focal plane. Astigmatism can be cancelled by including a third curved optical element. When this element is a mirror,

3640-508: The scientific objectives of CRIRES+ is in-transit spectroscopy of exoplanets, which currently provides us with the only means of studying exoplanetary atmospheres. Transiting planets are almost always close-in planets that are hot and radiate most of their light in the infrared (IR) . Furthermore, the IR is a spectral region where lines of molecular gases like carbon monoxide (CO) , ammonia (NH 3 ) , and methane (CH 4 ) , etc. are expected from

3705-487: The secondary mirror blocks a central portion of the aperture. This ring-shaped entrance aperture significantly reduces a portion of the modulation transfer function (MTF) over a range of low spatial frequencies, compared to a full-aperture design such as a refractor. This MTF notch has the effect of lowering image contrast when imaging broad features. In addition, the support for the secondary (the spider) may introduce diffraction spikes in images. The radii of curvature of

3770-608: The telescope at the Happy Jack site was received from the United States Forest Service in November 2004 and improvement of an existing road to the site commenced immediately. The primary mirror blank was completed by Corning in late 2005. Construction of the 26-meter-tall (85-foot), 19-meter-diameter (62-foot) telescope enclosure and an auxiliary support building began in mid-September 2005. Final figuring and polishing of

3835-485: The thin (177mm thick) mirror by computers. The VLT instrumentation programme is the most ambitious programme ever conceived for a single observatory. It includes large-field imagers, adaptive optics corrected cameras and spectrographs, as well as high-resolution and multi-object spectrographs and covers a broad spectral region, from deep ultraviolet (300 nm) to mid-infrared (24 μm) wavelengths. In addition to these, GRAVITY and MATISSE are currently installed in

3900-477: The use of large telescope diameters and adaptive optics correction can improve the sensitivity, this cannot extend the reach of optical interferometry beyond nearby stars and the brightest active galactic nuclei . Because the Unit Telescopes are used most of the time independently, they are used in the interferometric mode mostly during bright time (that is, close to full moon). At other times, interferometry

3965-601: Was identified as a comet using observations from the Discovery Channel Telescope. When the comet approached Earth within 2.2 million miles (about 9 lunar distances), the size of the nucleus to be calculated was 250 meters (820 feet) in diameter. The object was discovered by a PanSTARRS telescope, but not identified as a comet at that time. In 2017, the LDT achieved 282 nights out of the year (365 days) of scheduled observations for science. Ritchey%E2%80%93Chr%C3%A9tien telescope A Ritchey–Chrétien telescope ( RCT or simply RC )

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4030-428: Was initially designed to perform coherent integration (which requires signal-to-noise greater than one in each atmospheric coherence time). Using the big telescopes and coherent integration, the faintest object the VLTI can observe is magnitude 7 in the near infrared for broadband observations, similar to many other near infrared / optical interferometers without fringe tracking. In 2011, an incoherent integration mode

4095-493: Was introduced called AMBER "blind mode", which is more similar to the observation mode used at earlier interferometer arrays such as COAST, IOTA and CHARA. In this "blind mode", AMBER can observe sources as faint as K=10 in medium spectral resolution. At more challenging mid-infrared wavelengths, the VLTI can reach magnitude 4.5, significantly fainter than the Infrared Spatial Interferometer . When fringe tracking

4160-831: Was only expected to be 4.2 m, but it turned out that a 4.3 m (14 ft) mirror could be used. According to Director Jeffrey Hall, the telescope's original intent was for the study of comets, exoplanets, star formation in the Milky Way and other outer solar system projects. Other research includes observing the Kuiper belt , and exploring distant stars and galaxies. The telescope will make space exploration easier, more effective, and efficient for existing programs as well. Initial Project Leaders include Dr. Jeffrey Hall, Director, Lowell Observatory; Dr. Stephen Levine, Commissioning Scientist; Bill DeGroff, Project Manager; Byron Smith, Project Manager; Dr. Edward Dunham, Instrument Manager; and Ralph Nye, Director of Technical Services. P/2016 BA14

4225-421: Was some confusion as to whether Yepun actually stands for the evening star Venus, because a Spanish-Mapuche dictionary from the 1940s wrongly translated Yepun as "Sirius". Although the four 8.2-metre Unit Telescopes can be combined in the VLTI , their observation time is spent mostly on individual observations, and are used for interferometric observations for a limited number of nights every year. However,

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