Atacama Pathfinder Experiment

Atacama Pathfinder Experiment

The APEX telescope
Organisation	Max Planck Institute for Radio Astronomy (50%), Onsala Space Observatory (23%), ESO (27%)
Location(s)	Chajnantor plateau, Chile
Coordinates
Altitude	5,100 m
Weather	good
Wavelength	millimetre and submillimetre (0.2 to 1.5 mm)
Built	– (–)
First light	2005
Telescope style
Diameter	12-metre antenna
Collecting area
Mounting	altazimuth
Website	www.apex-telescope.org and www.eso.org/public/teles-instr/apex.html
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The Atacama Pathfinder Experiment (APEX) is a radio telescope 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert in northern Chile, 50 km east of San Pedro de Atacama. The main dish has a diameter of 12 m 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 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 that 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.

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%. The telescope was designed and constructed by the German firm VERTEX Antennentechnik GmbH, under contract by MPIfR. The operation of APEX in Chajnantor is entrusted to ESO.

Science

APEX instrument for finding water in the Universe.

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.

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. 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.

No fewer than 26 articles based on early science with APEX were published in July 2006 in a special issue of the research journal Astronomy and 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.

Recent APEX observations lead to the first ever discovery of hydrogen peroxide in space, 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, and the first direct measurements of the size and brightness of regions of star-birth in a very distant galaxy.

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 one year after they have been delivered to the principal investigator of the project.

Instruments

APEX Stands Sentry on Chajnantor.

Combined APEX and Spitzer data in an area known as Extended Chandra Deep Field South.

APEX, the largest submillimetre-wavelength telescope operating in the southern hemisphere, has a suite of 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. 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 — 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.

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).

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

Technology

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 12 m diameter of the antenna, the deviation from the perfect parabola is less than 17 thousandths of a millimetre. This is smaller than one fifth of the average thickness of a human hair.

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

Gallery

• Place to Unveil the Mysteries of the Cold Universe.jpg

  Panoramic view of the plateau.

• Setting the Dark on Fire.jpg

  Setting the Dark on Fire

• 

  APEX and clusters of white penitentes.

• 

  The APEX Antenna

• 

  Looking over to the ALMA site

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  APEX at Chajnantor

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  Image taken from APEX using solargraphy

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  Central region of the Milky Way (LABOCA on APEX)

• RCW 120 eso0840a.jpg

  Colour composite image of RCW 120 (LABOCA)

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  APEX 12m Telescope

External links

• Official website
• ESO APEX website
• Sub-millimetre Astronomy in Full Swing on Southern Skies — ESO Organisational Release