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Interferometer Receivers Mounted on PARI Telescopes

Receiver is readied for hoisting. Photo by Perry Hebard.ASHEVILLE NC – Installation Caps Six-Year Project by Scientists and Students at UNC Asheville, Furman University and PARI, to Design and Build Equipment that will Detect Rarely Observed Events in Space.  Six years of design, engineering and computer programming were brought to a climax this week with the hoisting and mounting of two highly specialized receivers onto radio telescopes at the Pisgah Astronomical Research Institute (PARI), in Transylvania County, N.C. Faculty and students at UNC Asheville and Furman University, and PARI staff, designed and constructed this new instrument for studying signals from space. The two custom-built receivers, each mounted on PARI’s 26-meter radio telescopes, will be linked using specialized, high-speed computers to create a complex piece of equipment called an interferometer.

A team led by Brian Dennison, UNC Asheville’s Glaxo Wellcome Professor and professor of Physics, will use the interferometer to monitor some fifty distant quasars for “extreme scattering events.” These rare disturbances in interstellar space distort the otherwise fairly constant signals from quasars and have only been detected about a dozen times. Dennison was part of a group of scientists that first discovered this rare phenomenon 25 years ago. Securing a series of grants from the National Science Foundation totaling more than $1 million, Dennison led the effort to design and build the new interferometer, which he calls the best tool for monitoring and learning more about extreme scattering events.

PARI is dedicated to providing hands-on educational and research opportunities for a broad cross-section of users in science, technology, engineering and math (STEM) disciplines. “This interferometer project is a perfect application of PARI’s goal to have scientists and students working side by side on our campus,” said PARI President Don Cline. “PARI’s Facilities Director Thad McCall, Site Engineer Ben Goldsmith and the entire PARI team did a magnificent job installing these receivers into our 26-meter radio telescopes. It was a great collaborative effort with Dr. Dennision and UNC Asheviille. The result is a world-class research-grade instrument of which we can all be proud.”

The first receiver is hoisted 75 feet in the air for installation. Photo by Perry Hebard.The installation was completed Tuesday and Wednesday, Dec. 12 and 13. On Tuesday, the receiver boxes, each weighing more than 1,500 pounds, were hoisted 75 feet off the ground by crane and installed by skilled PARI staff in raised buckets. Wednesday morning, the work crew checked the receivers’ positioning, bolted the equipment in, and attached tubing to bring in dry air; a dehumidified environment is crucial for some of the components.

Faculty and student interns worked during semester breaks and in addition to their everyday work over six years to complete the project. Said Dennison, “At national observatories, the engineers have the equipment set up, you take your data and leave. That is efficient but it means that scientists and students don’t necessarily get their hands on the equipment they’re using. Here, it’s nuts and bolts from the get-go, and our students are intimately involved with the instrumentation, which is a great experience. If you’re involved in the design of equipment, you know what it’s capable of and can come up with new applications. It is wonderful that PARI provides this unique environment for undergraduate students to gain experience they cannot get elsewhere.”

Brian Dennison (left) and Joseph Daugherty. Photo by Perry Hebard.Many people have been crucial to the interferometer project, including Joseph Daugherty, recently retired UNC Asheville professor of computer sciences; Chuck Bennett, UNC Asheville physics professor and director of PARSEC (Pisgah Astronomical Research and Science Education Center, a research center of UNC Asheville); Michael Castelaz, PARI astronomer; Don Cline, PARI director; and David Moffett, Furman University associate professor of Physics.

UNC Asheville student interns also played key roles in constructing the interferometer receivers. Junior Mechatronics Engineering major Micah Prendergast worked through the summer debugging the temperature and humidity control systems, and designing the specialized door hinge system. He wasn’t able to observe the installation because he was studying for a final exam, but upon hearing that it was successful, he said, “All of us feel like a weight lifted off of our shoulders, to know that it’s up there. Of course, my feelings aren’t comparable to what the professors who’ve spent years on this must be feeling.” Prendergast will likely stay involved, tweaking and maintaining the equipment he helped create.

Daugherty, although retired, will continue to update and troubleshoot the software programming he created for the interferometer’s computer system. The hardware correlator at the heart of the interferometer system was built by a team at the University of California, Berkeley. It processes data at one trillion bytes per second and has the computing power of several hundred conventional PCs.

Dennison confessed to “only a little bit” of nervousness when the telescope dishes were rotated for the first time Wednesday morning with six years of work attached. “Everything remained perfectly rigid – the PARI staff did a great job.” said Dennison. “This was a tremendous milestone for us. Now we can start testing the system. In early January, we’ll begin the process of commissioning, actually getting the system working as an astronomical interferometer and calibrating all of its properties.”

Once the interferometer becomes fully operational sometime this spring, Dennison and his colleagues will begin generating the data that may help reveal the cause of extreme scattering events. Dennison believes the likely cause is shock waves in the interstellar medium, but a few scientists believe that dark matter is the cause. “If they are right, that would be the discovery of dark matter, which would be a huge event,” says Dennison. “While that would be exciting, I fully expect that we are seeing the effects of gas compressed by violent shock waves such as those caused by supernova explosions.”

While only about a dozen extreme scattering events have been observed to this point, Dennison is expecting the new interferometer to lead to observations of such events perhaps on an annual basis. These interstellar disturbances last about a month or longer, and once they are discovered with the interferometer at PARI, other observatories around the globe will also monitor the event to provide more refined data. “I think we’ll be busy,” said Dennison. “I’m really anxious to get started.”

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