Pre-HEAT
PreHEAT telescope integrated onto PLATO in Sydney
The submillimeter-wave instrument on PLATO is called Pre-HEAT. Its name reflects that it is a prototype for the HEAT (High Elevation Antarctic Terahertz) telescope, a larger, more sophisticated telescope which is targeted for deployment on the 2010 timeframe. Pre-HEAT will perform astronomical observations and measure the transparency of the sky above Dome A at submillimeter wavelengths using a high frequency heterodyne receiver. The principles behind the operation of Pre-HEAT's heterodyne receiver are very similar to an ordinary FM radio. However, the Pre-HEAT receiver is many orders of magnitude more sensitive and is operating at frequencies that are 6600 times higher -- 660 GHz, or equivalently 0.66 THz.
Why Submillimeter Astronomy?
Of the many varied "colors" in the electromagnetic spectrum of light, submillimeter-waves are perhaps the last unexplored frontier. Nestled between traditional radio astronomy and optical/infrared astronomy, the submillimeter part of the spectrum is one of the richest treasure-troves for understanding the cold gas in galaxies that gives rise to the formation of stars and planets. On a larger scale, distant galaxies give off prodigious amounts of thermal energy at submillimeter wavelengths. It is possible that the oldest and most distant galaxies in the Universe will be detected at submillimeter wavelengths.The submillimeter-wave Universe has gone mostly unexplored because of the difficulty of instrumentation, and the fact that even minute traces of water vapor in the air absorb submillimeter light from space before reaching the ground. Thus, submillimeter-wave telescopes must be placed on the highest, driest sites on the planet. Large telescopes have already been placed on sites like Mauna Kea, Hawaii and (increasingly) on the high plains of the Atacama desert in northern Chile. However, because cold air holds less water vapor than warm air, expectations are that the high plateau of Antarctica will be even better, due to the extreme conditions which prevail there.
This was the motivation for building the prototype Pre-HEAT telescope for PLATO.
Site Testing
To measure the transparency of the sky above Dome A, the Pre-HEAT telescope scans the sky in elevation while measuring its brightness. The following sketches depict what Pre-HEAT would see in three different weather scenarios:
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If the submillimeter-wave sky is exceptionally clear, then Pre-HEAT will see a dark, cold sky at all elevation angles, from the zenith to the horizon. |
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In imperfect weather, the sky will be most opaque looking toward the horizon, through the most air. It will be clearest looking straight up, through the least amount of air. Thus, Pre-HEAT will see a darker and colder sky near zenith, getting gradually brighter and warmer as it looks toward the horizon. |
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If the submillimeter-wave sky is mostly opaque, then Pre-HEAT will see a bright, warm sky at all elevation angles, but especially so toward the horizon, where it must look through the greatest amount of air. |
Data collection began on 24 January 2008, with fully automated operation beginning in early March. Aside from some loss of receiver sensitivity compared to lab tests in Sydney, the instrument is working well and providing good measurements of the submillimeter sky over Dome A. Below is a single data measurement from early February, demonstrating that even in comparatively poor summer weather, the atmospheric transparency above Dome A is exceptional! In this single example, if you were to collect all of the water vapor over Dome A and condense it into an ocean, it would be only 0.22 millimeters deep. During the depths of the Antarctic winter, we expect it to get ~4 times drier still!
 By measuring how the sky brightens from zenith to horizon, Pre-HEAT measures the transparency of the atmosphere at submillimeter (radio) wavelengths. |
 Careful modeling of the atmosphere turns Pre-HEAT's measurements of the sky into a measurement of the total amount of water vapor over Dome A. Not only is this measurement important to astronomy, it is also relevant to our understanding of climate change on Earth! |
Astronomical Measurements
Pre-HEAT is a complete submillimeter-wave observatory. Not only does Pre-HEAT measure the atmosphere above Dome A, but it is also capable of performing detailed astronomical observations. Over the course of the season, Pre-HEAT will perform spectroscopic observations of the plane of the Milky Way in the light of the carbon monoxide (CO) molecule, our best tracer of the dark, cold clouds of gas and dust in interstellar space from which all stars are born.
Pre-HEAT's surveys will lead the way toward the even higher frequency surveys of atomic carbon, ionized carbon, ionized nitrogen, and CO to be performed by the follow-on HEAT telescope, which will help us understand how molecular clouds themselves are born in our Galaxy. Since we as human beings were an eventual product of these clouds' evolution, the mystery that Pre-HEAT and HEAT will help solve is a part of the story of our own origins!
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This infrared image of the Milky Way, taken by the 2MASS survey, shows the rich assemblage of stars, dust and gas that comprises our Milky Way Galaxy. Pre-HEAT will detect regions where cold and dark molecular clouds give birth to new stars, and the follow-on HEAT telescope will learn how these clouds are made! |
Learn more!
Coming in March 2008, the main web site for the current status of Pre-HEAT and information about HEAT is:
http://soral.as.arizona.edu/preheat/
http://soral.as.arizona.edu/heat/
Contacts
Craig Kulesa at the University
of Arizona, Tucson (USA)
Chris Walker at the University
of Arizona, Tucson (USA)
Mark McCaughrean at the University
of Exeter (UK)
Nick Tothill at the University
of Exeter (UK)
Participating institutions in alphabetical order
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Pre-HEAT was made possible by a Small Grant for Exploratory Research (SGER) from the National Science Foundation (ANT-0735854). |
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European Commission (Sixth Framework Programme - grant MIRG-CT-2006-044961) |
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Purple Mountain Observatory, China |
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University of Arizona, USA |
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University of Exeter, UK |
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University of New South Wales, Australia |