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Radio telescopes awaiting erection at Cedar Flat site
Nine pedestals and six reflector dishes rest at the Cedar Flat site in the Inyo Mountains of eastern California, where they eventually will be joined by six other telescopes operated by Caltech to form the Combined Array for Research in Millimeter-wave Astronomy. (Dick Plambeck photo)

Out with the BIMA, in with the ATA

– UC Berkeley's Hat Creek Observatory in northern California is undergoing a sea change as the nine 6.1-meter radio antennas of the Berkeley-Illinois-Maryland Array (BIMA) are dismantled and trucked south to the Inyo Mountains near Bishop to make way at the observatory for the world's largest radio telescope, the Allen Telescope Array (ATA).

All the pedestals and six of the nine BIMA reflector dishes are now resting at Cedar Flat near the California-Nevada border, awaiting better weather so that the remaining three dishes can make the long journey via backroads and freeways with a Highway Patrol escort. Next year, these nine antennas will be set up and joined by the six 10.4-meter radio dishes of Caltech's Owens Valley Radio Observatory to form a new Combined Array for Research in Millimeter-wave Astronomy (CARMA) dedicated to galactic, extragalactic and solar system astronomy. CARMA is a joint venture of Caltech, UC Berkeley, the University of Illinois at Urbana-Champaign and the University of Maryland.

Convoy moves telescope dish
The first convoy of reflectors detours past Nevada’s Pyramid Lake on its way to Cedar Flat. The reflectors are 21 feet wide, so the Highway Patrol closed off sections of road to allow the trucks to pass. (Dick Plambeck photo)

The move is a prelude to construction of an ambitious 350-dish radio array at Hat Creek, which, when completed, will be the largest radio telescope in the world. It will be used to observe everything from black holes to distant galaxies, while at the same time searching for intelligent signals from space. The first 32 6.1-meter radio dishes of the ATA should be erected at Hat Creek by the end of the year, with first observations possible by spring.

Planning for the BIMA move started earlier this year, with UC Berkeley's Radio Astronomy Laboratory splitting each antenna in two and then contracting with Bigge Crane and Rigging to truck the pedestals and reflectors to Cedar Flat. The pedestals arrived without incident via three convoys in September. The extra-wide dishes were transported this month, requiring a Highway Patrol escort that often flagged cars off to the side of the road to allow passage of the trucks, which, with their 21-foot-wide loads, took up two lanes of traffic. The trek involved a detour north of Reno to Pyramid Lake to avoid underpasses and low-hanging electrical wires around the "Biggest Little City in the World." The final convoy arrived at the 7,300-foot Cedar Flat site on Oct. 15.

Reflector arrives at Cedar Flat
The first convoy of reflectors arrives at Cedar Flat. Oct. 14, 2004. (Curt Giovanine photo)

"It went quite smoothly, so far, but we still have three dishes to go. Hopefully everything will go well," said Dick Plambeck, a research astronomer who helped coordinate the move.

The 15 telescopes of the CARMA array will be movable, so that astronomers can trade off the sensitivity of a closely packed array with the fine resolution of the array when spread out, Plambeck said. Astronomers wanting to measure the emission from carbon monoxide throughout a big molecular cloud might want the antennas close together, while those mapping the dust disk around a distant star might spread out the antennas to resolve the pinpoint source. The array will be most sensitive in the radio bands around 1 millimeter and 3 millimeters.

"People have used the BIMA array to learn about the chemistry in a cold molecular cloud, to find the total mass of a star-forming region, or to track a cloud's motion and dynamics," he said. "Molecular clouds are mostly hydrogen, but since molecular hydrogen is hard to measure, we look at the CO as a proxy."

The high-elevation Cedar Flat site is better for millimeter-wave astronomy than Hat Creek, Plambeck said, because there is less water vapor to interfere with radio observations. Conversely, Hat Creek is situated in a shallow valley in the southern Cascade range and thus has less radio interference, which could disrupt the sensitive measurements planned with the ATA.

Close-up of reflector dish
Telescope reflector dishes and pedestal sit side by side at Cedar Flat. (Curt Giovanine photo)

The full 350-antenna ATA will have unprecedented sensitivity over a large range of wavelengths centered in the centimeter radio band, spanning the equivalent of about four and a half octaves. The receivers of most radio telescopes span less than half an octave, and optical telescopes span perhaps one or two. The wavelength range stretches from 2 to 50 centimeters, including the important 21.1-centimeter radio emissions of cold hydrogen that have allowed astronomers to map the Milky Way galaxy's spiral arms.

As astronomers use the ATA to study galaxies, dust clouds or black holes, others will be analyzing the radio signals for patterns that indicate they came from intelligent civilizations far, far away. The ATA is a joint project between UC Berkeley and the SETI Institute of Mountain View, Calif., funded by $25 million from investor and philanthropist Paul G. Allen, and another $1 million from former Microsoft Chief Technology Officer Nathan P. Myhrvold. Another $16 million is needed to expand the array from 32 to 206 dishes, on the way to a full 350-dish array. Some development costs also are being funded by the National Science Foundation.

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