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Allen Telescope Array Fact Sheet
The Allen Telescope Array (ATA) —formerly known as the One Hectare Telescope (1hT)— is a joint effort by the SETI Institute and the Radio Astronomy Laboratory at the University of California, Berkeley to construct a Radio Interferometer that will be dedicated to astronomical and simultaneous search for extra-terrestrial intelligence observations. It is being constructed at the Hat Creek Radio Observatory, 290 miles northeast of San Francisco, California and will be composed of 350 antennas at completion.
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Contents
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Background
The idea has been a dream of the SETI Institute for years. However, it was not until early 2001 that research and development commenced after a donation of $11.5 million USD by the Allen Foundation. In March 2004, the SETI Institute unveiled a three tier construction plan for the telescope, following a successful completion of a three-year research and development phase. Construction began right after, thanks in part to the generous donation of $13.5 million USD by Paul Allen (co-founder of Microsoft) to support the construction of the first and second phases. The SETI Institute named the telescope in his honor.
Overview
The ATA is a centimeter-wave array that pioneers the Large-Number Small-Diameter (LNSD) concept of building radio telescopes. By taking advantage of Moore’s Law, the designers are replacing steel with silicon, resulting in a large cost saving over telescopes of more conventional design.
The ATA has four primary advantages for scientific studies over all ma jor radio telescopes built to date: a very wide field-of-view (2.45° at λ = 21cm), complete instantaneous frequency coverage from 0.5 to 11.2 GHz, multiple simultaneous backends, and active interference mitigation. The instantaneous area of sky imaged is 17 times that of the VLA. The instantaneous frequency coverage of more than 4 octaves is unprecedented in radio astronomy and is the result of a unique feed, input amplifier, and signal path design. Active interference mitigation will make it possible to observe even at frequencies of many terrestrial radio emitters.
Artist Rendering of ATA-350
Credit: Isaac Gary
(Click to enlarge)
Because all-sky surveys are an important part of the science program, the efficiency of the ATA will be increased by doing radio astronomy and SETI searches simultaneously. The telescope will do this by splitting the signals in the control room prior to final processing. Simultaneous observations are possible because for SETI, several target stars will lie within the large field-of-view afforded by the 6m dishes wherever the telescope is pointed. Thus, by agreement between the RAL and the SETI Institute, the needs of conventional radio astronomy will determine the pointing of the array.
The ATA will ultimately comprise 350 6-meter dishes and will make possible large, deep radio surveys that were not previously feasible. The telescope incorporates many new design features including hydroformed antenna surfaces, a log-periodic feed covering the entire range of frequencies from 500 MHz to 11.2 GHz, low noise, wide-band amplifiers with a flat response over the entire band making it possible to amplify the sky signal directly.
The instrument will be operated and maintained by the Radio Astronomy Laboratory (RAL) at the University of California, Berkeley. The RAL has worked hand in hand with the SETI Institute during design and prototyping, is the primary designer of the feed, correlator and imaging system for Radio Astronomy observations.
The ATA is being constructed in 4 stages, the ATA-42, ATA-98, ATA-206, and ATA-350; each number representing the number of dishes in the array at a given time (See Table 1). When completed it will be one of the largest and most powerful telescopes in the world.
The astronomy decadal panel, Astronomy and Astrophysics in the New Millenium, endorsed SETI and recognized the ATA (then, the 1 Hectare Telescope) as an important stepping-stone to the Square Kilometer Array (SKA).
After its completion, ATA is expected to be among the world’s largest and fastest observing instruments. It will also permit SETI astronomers to search for signals from many different target stars simultaneously.
Key Science
The science goals listed here represent the goals of the most important projects that will be conducted over the next three years with the ATA. Each of these goals is associated with one of the 4 stages of development (see Table). The bulleted items are the projects that will be undertaken and the subtopics are some of the science that will be produced. The ATA will:
- Determine the HI content of galaxies over three quarters of the sky, to measure how much intergalactic gas external galaxies are accreting; to search for dark, starless galaxies; to lay the foundation for SKA dark energy detection
- Classify 250, 000 extragalactic radio sources as active galactic nuclei or starburst galaxies, to probe and quantify star formation in the local Universe; to identify high redshift objects; to probe large scale structure in the Universe; to identify gravitational lens candidates for dark matter and dark energy detection
- Explore the transient sky, to probe accretion onto black holes; to discover of the orphan gamma-ray burst afterglows; to discover new and unknown transient phenomena
- Survey 1,000,000 stars for extraterrestrial signals with enough sensitivity to detect an Arecibo radar out to 300 pc within the range of 1 to 10 GHz
- Survey the 4×1010 stars of the inner Galactic Plane near the "magic" frequency of 1420 MHz for very powerful transmitters
- Measure the magnetic fields in the Milky Way and other Local Group Galaxies, to probe the role of magnetic fields in star formation and galaxy formation
- Detect the gravity-wave background from massive black holes through pulsar timing
- Measure molecular cloud and star formation properties using new molecular tracers, to map the star formation conditions on the scale of entire GMCs; to determine the metallicity gradient of the Milky Way
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| Note. Beam size and continuum sensitivity (Srms are estimated for a 6 minute, 100 MHz continuum snapshot observation at transit of a source at 40° declination at a wavelength of 21 cm. Speed is given for a survey at 21 cm observations with a bandwidth of 100 MHz that reaches 1 mJy rms.
†ATHIXS is an all-sky deep HI extragalactic HI survey. |
Instrument Details
The ATA-42 configuration will provide a maximum baseline of 300m (and ultimately the ATA-350, 900m). A cooled log-periodic feed on each antenna is designed to provide a system temperature of ~ 45 K from 1 to 10 GHz, with reduced sensitivity in the range 0.5-1.0GHz and 10-11.2GHz. Four separate frequency tunings (IFs) are available to produce 4x100MHz intermediate frequency bands. Two IFs support correlators for imaging; two will support SETI observing. All tunings can produce four dual polarization phased array beams which can be independently pointed within the primary beam and can be used with a variety of dectectors. The ATA can therefore synthesize up to 32 phased array beams.
The wide field of view of the ATA gives it an unparalleled capability for large surveys. The time required for mapping a large area to a given sensitivity is proportional to (ND)² , where N is the number of elements and D is the diameter of the dish. This leads to the surprising result that a large array of small dishes can outperform an array with smaller number of elements but considerably greater collecting area at the task of large surveys. As a consequence, even the ATA-42 is competitive with much larger telescopes in its capability for both brightness temperature and point-source surveys. For point-source surveys, the ATA-42 is comparable in speed with Arecibo and the Green Bank Telescope (GBT), but slower by a factor of 3 than the Very Large Array (VLA). The ATA-350, on the other hand, is an order of magnitude faster than the Very Large Array for point- source surveys and is comparable to the Expanded VLA (EVLA) in survey speed. For surveys to a specified brightness temperature sensitivity, the ATA-98 exceeds the survey speed of even the VLA-D configuration. The ATA-206 matches the brightness temperature sensitivity of Arecibo and the GBT. The ATA, however, provides better resolution than either these single dish telescopes.
The antenna for the ATA is a 6.1m × 7.0m hydroformed offset Gregorian with a 2.4-meter subreflector with an effective f/D of 0.65. The offset geometry eliminates blockage, which increases the efficiency and decreases the sidelobes. It also allows for the large subreflector, providing good low frequency performance. The hydroforming technology used to make these surfaces is the same hydroforming technique used to generate low-cost satellite reflectors by Andersen Manufacturing (Idaho Falls, ID). The unique, interior frame rim-supported compact mount allows excellent performance at a low cost. The drive system employs a spring-loaded passive anti-backlash azimuth drive train.
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