UMass researchers to build South Pole receiver; expected to offer new perspectives on galactic evolution

Project funded by $1.79 million in major grants

AMHERST, Mass. – A team of researchers led by Sigfrid Yngvesson, professor of electrical engineering at the University of Massachusetts, has received three federal grants totaling more than $1.79 million to build and improve a receiver that can detect the presence of nitrogen plus, one of our galaxy’s basic components. To date, there is no receiver that can detect nitrogen plus from the Earth’s surface. The ability to map the location and amount of nitrogen plus "will provide a new perspective on stellar, chemical, and galactic evolution," Yngvesson said. The receiver will be built into an existing radio telescope at the South Pole, and will be designed to capture signals at one of the finest resolutions scientists have ever achieved from Earth’s surface. The three grants are from NASA and the National Science Foundation.

The project, under the direction of Yngvesson, and Eyal Gerecht of astronomy, will also involve researchers from UMass Lowell, the Harvard/Smithsonian Center for Astrophysics, the University of Arizona, and the University of Wales. The new receiver will be built into the existing AST/RO 1.7 m diameter submillimeter wave telescope at the U.S. South Pole Station. The telescope is operated by the Harvard/Smithsonian Center for Astrophysics.

Nitrogen plus, which is ionized nitrogen, was first detected by the Cosmic Background Explorer (COBE) satellite launched in 1989, Yngvesson said. Atoms and molecules are found throughout interstellar space. These chemicals send out signals at particular frequencies, which allow scientists to identify them. Nitrogen plus has been difficult to detect because the signal it emits is extremely high, at 1.5 terahertz (THz), he explained. That’s 100 times faster, or higher, than the signals received by a television satellite dish. In fact, the frequency of the signal from nitrogen plus is so high, it is largely blocked by water vapor in the atmosphere, and can only be detected by special receivers, he said. "Since the Antarctic is so dry, the problem of water vapor blocking the signal will be greatly reduced, and the atmosphere there is sufficiently transparent that one can take advantage of the new advances in receiver technology," said Yngvesson.

"In order to study space at even higher frequencies, one must eventually construct instruments for operation in space, or in high-flying airplanes and balloons," explained Gerecht. "The reason for this is that the atmosphere becomes essentially opaque as the frequency goes up. The technology of receivers for these higher frequencies has recently made enormous strides, and much more sensitive receivers are now available."

"Astronomers have successfully detected and studied a number of atomic and molecular species in the interstellar medium (ISM) of our galaxy, and a few even in quite remote galaxies, in the last few decades," notes Yngvesson. "These investigations have primarily been performed with radio telescopes which are outfitted with sensitive receivers in order to pick up very high-frequency radio waves from space. Our ability to do this has vastly improved as technology has improved."

The UMass receiver, currently in the prototype stage, is able to detect such high frequencies because the instrument itself is kept cold and because it uses a unique new superconducting device, explained Yngvesson. "Astronomers use instrumentation that’s very cold. When it’s cold, it’s much quieter," he said. "In order to listen to very weak signals from space, you have to go to extremes of keeping your receiver’s own intrinsic noise down." Currently, the most sensitive receivers must operate at four kelvin – four degrees above absolute zero. The goal of one of the NASA grants is to develop a prototype receiver that is expected to operate at 12 kelvin. Yngvesson explains that by raising the temperature by a factor of three, the receiver becomes at least three times less expensive to run. UMass has previously constructed a number of sensitive receivers, ranging from the millimeter wave telescope in the Quabbin reservoir watershed, to the ongoing Large Millimeter Wave Telescope (LMT) project and SWAS, a submillimeter satellite observatory now operating in space.

This will be the first astronomical receiver for frequencies well above 1 THz and will provide a testing ground for future uses of "low-noise" THz receivers in both airborne and spaceborne receivers. Researchers expect that the specialized receiver will be used in other ways in the future, as well. Some THz receivers are now being built to monitor the Earth’s atmosphere from space.

Details on the grants follow:

• The first NASA grant is for $822,000 over three years, plus an additional $30,000 for an educational and public outreach component.
• The second NASA grant from the Space Astrophysics Research and Analysis Program, is a subcontract through the National Institute of Standards and Technology (NIST) in Boulder, Co., and is for $258,000 over two years. The principal investigator at NIST is Erich Grossman.
• The National Science Foundation grant is for $684,000 over three years. The grant will go toward refining the terahertz receiver for use at the South Pole.

Note: Sigfrid Yngvesson can be reached at 413/545-0771 or [email protected]