Indiana University      Research & Creative Activity      April 1998 Volume XXI Number 2



Tabloid

Scoping the Skies

with WIYN, RoboScope, and SpectraBot

by Eric Pfeffinger


The office doors and bulletin boards in the halls of the Astronomy Department in Swain Hall West on the Bloomington campus are festooned with cartoons and tabloid articles that illustrate the hold astronomy exerts on the popular imagination. The sketches of aliens and Enquirer photos make it clear that, for better or worse, this serious and highly technical academic discipline enjoys a distinct cachet in the mass media.

One cartoon in the hallway also shows succinctly the chasm that exists between that popular perception and the day-to-day reality of astronomy. A youth in a classroom raises his hand and asks what the difference is between astronomy and astrology. "Lots and lots of math," the cartoon professor replies. The classroom clears out. Meticulous measurement and instrumentation aren't for everyone.

Honeycutt
R. Kent Honeycutt, Professor of Astronomy and Chairperson of the Department of Astronomy at IUB, is reflected in the primary mirror of IU's new fifty-inch telescope. The secondary mirror at the top of this Cassegraintype telescope, as well as part of the slit of the observatory dome, can also be seen in reflection. SpectraBot, as this new automated instrument is called, is located at the Morgan-Monroe Station of the Goethe Link Observatories, about twelve miles north of the Bloomington campus. --credit

At least one door in this hallway has no such ironic displays. Although R. Kent Honeycutt, professor of astronomy and chairperson of the Department of Astronomy, is good-humored and quick to smile, he's less overt about it. He is, however, intimately involved with the kinds of meticulous measurement and instrumentation that scared off the would-be cartoon astronomers. He relies on instrumentation because his research focus, accretion disks, are things no human has ever glimpsed.

"Accretion disks are fairly common in the universe, but no one's ever seen one," he explains. To understand what they are, one first has to understand the notion of "compact objects." "In most of my nontechnical talks I start by recognizing that most people think nuclear energy is the most powerful force in the universe, but the most exotic and brightest and hottest phenomena in nature"--compact objects--"are due to plain old gravity." Gravity is the force behind heavenly phenomena like white dwarfs, neutron stars, and black holes. Black holes get their name from their incredible density; they're so dense that even light can't escape their gravitational pull.

"There is no analogous material on Earth for compact objects," Honeycutt emphasizes. "White dwarfs have a density a million times that of water. It's completely foreign to our everyday experience."

Accretion disks can be formed when material, such as gas, falls toward one of these compact objects. The material, seized by the gravitational pull, spirals around the object, forming a disk. Often when a nearby star is losing its mass, that lost material forms the spiraling disk around the high-gravity object. "I've spent much of my professional life studying accretion disks," Honeycutt says. "They are the way nature has most often chosen to release gravitational energy."

Accretion
The strong gravity and rapid revolution of close binary stars sometimes combine to cause gas to flow from one star into a whirling accretion disk surrounding the companion star. If the mass-gaining star is a compact stellar object, such as a white dwarf, a neutron star, or a black hole, then friction can heat the infalling disk so the disk glows more brightly than either of the stars. Such accretion disk systems are often unstable, producing regular flaring activity know as dwarf nova, as well as more powerful and rare nova explosions. --credit

Honeycutt has begun to find a few surprises. "The theory of accretion disks was this: When they're hot enough, they should be stable," he says. That stability should preclude any irregular behaviors such as outbursts, or dwarf-nova-like cataclysmic eruptions. "But we've found that hot accretion disks nevertheless have outbursts no one had ever looked closely enough to see before," Honeycutt says. "This has led to revisions in our understanding of how accretion disks work. We're really just at the beginning--now that we know these outbursts occur, we can try to study how and why."

Obviously, this means more observation and measurement. For Honeycutt and his group, measurement and instrumentation aren't merely tools--they're part of a fundamental mindset. "Everyone has a different way of approaching a problem. My group traditionally has built a new instrument to gather new kinds of data. That's not the only way to do it: you could build a new computer model or reserve time at a national observatory. But we take the instrumental approach." So when Honeycutt's team runs up against the problem of distortions caused by the Earth's atmosphere--the "twinkling" of a star, for instance--they work to design a new instrument that will move the telescope's secondary mirror and achieve greater resolution. "Rather than getting more time on a bigger telescope, we're trying to use image stabilization to collect higher quality data on our smaller telescopes," Honeycutt says.

In another area of research closer to Earth, Honeycutt and his group found it difficult to study the fainter regions around Saturn, so they again took the instrumental approach. Recognizing that the problem was the overpowering light from the bright planet itself, the team built a specialized coronagraph, a device that blocks the light of a central object to render the object's fainter parts more visible. Using the WIYN 3.5-meter telescope in Arizona, the technique was used to study Saturn's fainter rings and small moons as Earth passed through the plane of Saturn's rings in 1996. WIYN (pronounced "win") is so named because it was developed by a consortium of Wisconsin, Indiana, Yale, and the National Optical Astronomy Observatories. The precise WIYN optics and the WIYN electronic imaging system, built at Indiana, gave excellent coronographic images for the Saturn experiment, one of the first observations at the new observatory. "With a name like WIYN," Honeycutt jokes, "we just expect all the experiments there to be successful."

Honeycutt
High quality sites for research telescopes are high, dry, and dark. The WIYN Observatory is atop 6,900-foot Kitt Peak, about forty-five miles southwest of Tucson, Arizona, on the land of the Tohono O'Odham Indian Nation. --credit

The instrumental approach has been key in Honeycutt's recent work. Tucked away among the winding roads and remote beauty of the Morgan-Monroe State Forest is an observatory (a station of the Goethe Link Observatories that Honeycutt directs) collecting some of his data. What makes both the older sixteen-inch telescope and the new fifty-inch telescope in the forest distinctive is their extensive level of automation. "Automation for small telescopes isn't unusual," Honeycutt says. "What is unusual is automation for very faint electronic imaging like we're doing with our sixteen-inch telescope. We were, I think, the first in the world to do that, and still no one else does spectroscopy with automation. Yet spectroscopy--analyzing light from stars to detect chemical composition, physical conditions, and movement--is just what IU's new fifty-inch telescope will do."

Automation is crucial in Honeycutt's instrumentation because, he says, "the time scales involved in the behavior of accretion disks are longer than you can conveniently study in a few days. Nature doesn't accommodate astronomers' day-night schedules; these things happen over the course of weeks or months and so can only be studied with a dedicated facility like this." Only automation enables the production of long, homogeneous data streams revealing the nature and behavior of irregularities like outbursts. Honeycutt has been regularly observing some objects for nearly eight years now, which promises entirely new levels of accuracy and discovery.

Every night, if the observatory's sensor--a little wire grid mounted outside the building--determines it isn't raining or snowing, and if a tiny external telescope aimed at Polaris determines that visibility is sufficient, the slot in the white dome slides open and the older high-tech telescope, looking with its homemade additions like a hybrid of NASA and science fair, automatically goes to work. The black mirror cover, like a felt-covered cymbal on an archaic robotic arm, swings away and the telescope comes to life. It tilts and whirs and rotates until, by morning, it has collected four-minute exposures of approximately 100 heavenly objects on its program. It can even make decisions about altering its program if sufficiently significant anomalies appear.

"Sometimes a week goes by with no one out here," Honeycutt says, and he estimates that the telescope's eyepiece probably hasn't been used for years. With a few keystrokes on a computer terminal he demonstrates how just about everything the telescope does can be monitored remotely. From home or his office in Swain West, with either a textual or graphical computer interface, Honeycutt can check on the telescope's temperature, the position of the nitrogen probe (liquid nitrogen is used to cool the sensitive image detector), the area's relative humidity, the status of the dome slit, the direction of the telescope, and dozens of other variables. He can also override program elements from afar. The tyranny of needing a human being at the observatory to collect data has been overthrown.

Telescope
The WIYN 3.5-meter telescope provides superior image sharpness by controlling the temperature of the dome, telescope, and optics, as well as the shape of the primary mirror and the tilt of the secondary mirror. In this view, the primary mirror is hidden in the lower structure and the secondary mirror is inside the black cylindrical baffle at the top of the telescopes. The large instrument attached to the near side of the telescope is part of the WIYN Multiple Object Spectrograph. --credit

This past winter, however, the observatory has been heavily populated. The team building the new telescope--students, retired faculty, electronic engineers--lends the observatory an ambience of scruffy and casual camaraderie with their stocking caps, sweatshirts, and shaggy beards. "We call it a clubhouse," says Honeycutt, who, in his sweater-vest, looks decidedly paternal. The students named the telescopes; the older one is RoboScope and the new one has already been christened SpectraBot- although Honeycutt voted for what he calls "the more prosaic name of 'automated photometric telescope.'" The livelier names prevailed, and RoboScope is now cited in the scholarly papers produced by Honeycutt and his colleagues.

On one occasion a debate erupts regarding the setting and placement of the telescope's 325-pound, 1.25-meter mirror. "We argue every step of the way," one team member asserts in a delighted aside. "We've got these heavy, massive things and yet they're very accurate and fragile," another chimes in. "We're using techniques you might use in the junkyard, only very, very carefully."

"It is a team effort," Honeycutt says, "and has to be. There are so many skills involved. We've developed within the astronomy department bits and pieces of engineering skills: optical design, electronics, vacuum technology."
Already accustomed to collaboration, Honeycutt hopes the new Linda and Jack Gill Center for Instrumentation and Measurement Science will foster cooperation across disciplines by encouraging more interaction among the several departments that work with precise measurements. "We have to work to avoid compartmentalizing," he says. "To the extent the Gill Center gets us talking to each other, it will be a success. And that's not even a particularly ambitious thing. Hopefully truly cross-disciplinary projects can emerge in both the research and instructional areas of instrumentation design."

Meanwhile, Honeycutt will continue his work, which promises to bring rewards both personal and disciplinary. "I just like working with my hands," he says. "I like machinery and neat physical objects. I like building machines that'll do things. That's the day-to-day satisfaction of it. You need a little bit of an engineering mentality, even on a campus with no engineering school."

Continuing to do what he likes may lead to discoveries with wider implications; the significance of accretion disks is not just academic. "I always tell my undergraduate classes: We are made of star stuff," Honeycutt says. "Calcium, phosphorus, iron: these don't exist most places in the universe. There are lots of heavy chemical elements in our part of the solar system, and that's lucky for us. Accretion disks are part of the process of the formation of planets and could have a lot to do with how our solar system formed." In short, the remote data collected by RoboScope and SpectraBot hits pretty close to home. As close as the Morgan-Monroe State Forest, in fact. That's why, night after night into the next millennium, gleaming white domes in Indiana and at WIYN in Arizona will turn, slits will slide open, and three quirkily named telescopes will watch the skies. dingbat


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