Atacama Pathfinder Experiment

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Atacama Pathfinder Experiment (APEX)[1]
The APEX telescope
Organization Max Planck Institute for Radio Astronomy (50%), Onsala Space Observatory (23%), ESO (27%)[2]
Location Chajnantor plateau, Chile
Coordinates 23°00′21″S 67°45′33″W / 23.00583°S 67.75917°W / -23.00583; -67.75917Coordinates: 23°00′21″S 67°45′33″W / 23.00583°S 67.75917°W / -23.00583; -67.75917
Altitude 5,100 m
Weather good
Wavelength millimetre and submillimetre (0.2 to 1.5 mm)
First light 2005
Diameter 12-metre antenna
Mounting altazimuth
Website and

The Atacama Pathfinder Experiment (APEX) is a radio telescope located at 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert, in northern Chile, 50 kilometers to the east of San Pedro de Atacama. The main dish has a diameter of 12 meters and consists of 264 aluminium panels with an average surface accuracy of 17 micrometres (r.m.s.). The telescope was officially inaugurated on September 25, 2005.

The APEX telescope is a modified ALMA (Atacama Large Millimeter Array) prototype antenna and is located at the site of the ALMA observatory. APEX is designed to work at sub-millimetre wavelengths, in the 0.2 to 1.5 mm range — between infrared light and radio waves, and to find targets which ALMA will be able to study in greater detail. Submillimetre astronomy provides a window into the cold, dusty and distant Universe, but the faint signals from space are heavily absorbed by water vapour in the Earth's atmosphere. Chajnantor was chosen as the location for such a telescope because the region is one of the driest on the planet and is more than 750 m higher than the observatories on Mauna Kea, and 2400 m higher than the Very Large Telescope (VLT) on Cerro Paranal.[1]

APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR) at 50%, Onsala Space Observatory (OSO) at 23%, and the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) at 27%.[2] The telescope was designed and constructed by VERTEX Antennentechnik GmbH (Germany), under contract by MPIfR.[3] The operation of APEX in Chajnantor is entrusted to ESO.


Observations made with the ESO's APEX telescope reveal the cold dusty clouds from which stars form in the Carina Nebula.[4]

Submillimetre astronomy is a relatively unexplored frontier in astronomy and reveals a Universe that cannot be seen in the more familiar visible or infrared light. It is ideal for studying the "cold Universe": light at these wavelengths shines from vast cold clouds in interstellar space, at temperatures only a few tens of degrees above absolute zero. Astronomers use this light to study the chemical and physical conditions in these molecular clouds — the dense regions of gas and cosmic dust where new stars are being born. Seen in visible light, these regions of the Universe are often dark and obscured due to the dust, but they shine brightly in the millimetre and submillimetre part of the spectrum. This wavelength range is also ideal for studying some of the earliest and most distant galaxies in the Universe, whose light has been redshifted into these longer wavelengths.[1]

APEX science goals include studying the formation of stars, planets, and galaxies, including very distant galaxies in the early Universe, and the physical conditions of molecular clouds.[1] Its first results proved the telescope lives up to the ambitions of the scientists by providing access to the "Cold Universe" with unprecedented sensitivity and image quality. As a demonstration, no less than 26 articles based on early science with APEX were published in July 2006 in a special issue of the research journal Astronomy & Astrophysics. Among the many new findings published then, most in the field of star formation and astrochemistry, are the discovery of a new interstellar molecule, and the detection of light emitted at 0.2 mm from CO molecules, as well as light coming from a charged molecule composed of two forms of Hydrogen.[5]

Recent APEX observations lead to the first ever discovery of hydrogen peroxide in space,[6] the first image of a dusty disc closely encircling a massive baby star, providing direct evidence that massive stars form in the same way as their smaller brethren,[7] and the first direct measurements of the size and brightness of regions of star-birth in a very distant galaxy.[8]

All ESO and Swedish APEX data are stored in the ESO archive. These data follow the standard ESO archive rules, i.e. they become publicly available 1 year after they have been delivered to the principal investigator of the project.[9]


APEX Stands Sentry on Chajnantor.[10]
Combined APEX and Spitzer data in an area known as Extended Chandra Deep Field South.[11]

APEX, the largest submillimetre-wavelength telescope operating in the southern hemisphere, has a suite of different instruments for astronomers to use in their observations, a major one being LABOCA, the Large APEX Bolometer Camera. LABOCA uses an array of extremely sensitive thermometers — known as bolometers — to detect submillimetre light. With almost 300 pixels, it is the largest such camera in the world. In order to be able to detect the tiny temperature changes caused by the faint submillimetre radiation, each of these thermometers is cooled to less than 0.3 degrees above absolute zero — a frigid minus 272.85 degrees Celsius. LABOCA's high sensitivity, together with its wide field of view (one third of the diameter of the full Moon), make it an invaluable tool for imaging the submillimetre Universe.[1]

For its first observations, APEX was equipped with state-of-the-art sub-millimetre spectrometers developed by MPIfR's Division for Sub-Millimetre Technology and, more recently, with the first facility receiver built at Chalmers University (OSO).[3]

For more information about APEX instruments, consult the instrumentation page.


In order to operate at the shorter sub-millimetre wavelengths, APEX presents a surface of exceedingly high quality: after a series of high precision adjustments, the APEX project team was able to adjust the surface of the mirror with remarkable precision: over the 12m diameter of the antenna, the deviation from the perfect parabola is now less than 17 thousandths of a millimetre. This is smaller than one fifth of the average thickness of a human hair.[3]

The Apex telescope is made up of three "receiver" cabins : Cassegrain, Nasmyth A and Nasmyth B.



  1. ^ a b c d e "ESO - APEX". ESO. Archived from the original on 22 June 2011. Retrieved 2011-06-14. 
  2. ^ a b "APEX - Atacama Pathfinder EXperiment". Archived from the original on 24 June 2011. Retrieved 2011-06-14. 
  3. ^ a b c "New Sub-Millimetre Light in the Desert — APEX telescope Sees First Light at Chajnantor". ESO. 2005-07-14. Retrieved 2011-08-19. 
  4. ^ "The Cool Clouds of Carina". ESO Photo Release. Retrieved 16 November 2011. 
  5. ^ "Sub-millimetre Astronomy in Full Swing on Southern Skies — Impressive set of APEX Results to be published in Special Issue of Astronomy & Astrophysics". ESO. 2006-07-13. Retrieved 2011-08-19. 
  6. ^ "Hydrogen Peroxide Found in Space". ESO. 2011-07-06. Retrieved 2011-08-19. 
  7. ^ "Unravelling the Mystery of Massive Star Birth — All Stars are Born the Same Way". ESO. 2010-07-14. Retrieved 2011-08-19. 
  8. ^ "APEX Snaps First Close-up of Star Factories in Distant Universe". ESO. 2010-03-21. Retrieved 2011-08-19. 
  9. ^ "APEX data archiving". Archived from the original on 25 July 2011. Retrieved 2011-08-19. 
  10. ^ "APEX Stands Sentry on Chajnantor". ESO Picture of the Week. Retrieved 16 April 2012. 
  11. ^ "The Wild Early Lives of Today's Most Massive Galaxies". ESO Press Release. Retrieved 27 January 2012. 
  12. ^ "Setting the Dark on Fire". ESO Press Release. Retrieved 12 February 2013. 

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