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September 1, 2016

Scanning the night skies: Pitt part of worldwide effort to discover new planets

Physics and astronomy faculty member Michael Wood-Vasey,

Physics and astronomy faculty member Michael Wood-Vasey,

On Aug. 24, the world was surprised to learn a potentially habitable, rocky planet that could contain the essential ingredient of life — water — was detected around the nearest star, Proxima Centauri, a mere 4.2 light-years away — albeit a planet that orbits its red star so closely it has only an 11-day year.

Such news would not surprise the physics and astronomy majors in Pitt’s STEPUP program: the Survey of Transiting Extrasolar Planets at the University of Pittsburgh (, an undergraduate research project overseen by Michael Wood-Vasey, faculty member in physics and astronomy.

Since August 2009, STEPUP has used a 16-inch telescope at Pitt’s Allegheny Observatory on the North Side to take part in a worldwide effort to find new planets around stars other than our sun — “exoplanets” — as they cross, or “transit,” the face of their star. STEPUP has used many nights of observation to confirm planets previously detected by other research groups and contribute this data to an international planetary database. STEPUP also is participating in a Hubble telescope program looking at a small set of stars to refine exoplanet-detecting methods.

 Observatory manager Lou Coban, with the project’s 16-inch telescope

Observatory manager Lou Coban, with the project’s 16-inch telescope

The first exoplanet was discovered in 1995 and dubbed a “hot Jupiter,” since it is a gas giant similar to Jupiter but orbiting much closer to its sun, which is 50 light-years from Earth. Researchers found the first planetary system in 1999, and one of the smallest exoplanets in 2005, just seven-and-a-half times the mass of Earth. Since then other, more Earthlike, rocky planets have been detected, albeit with conditions that may preclude potential life, such as being “tidally locked,” with one side always facing away from their suns, creating prohibitively hot or cold conditions on either side.

The first potentially habitable planet was observed in 2011, called Kepler-22b. It is a rocky planet in an orbit that would allow water to be liquid — its average surface temperature is estimated at 72 degrees — but its mass would result in a gravity 36 times that of Earth, which is not exactly friendly to life as we know it.

Other planets have since been under observation by STEPUP and various research programs, but none as close as the planet around Proxima Centauri, dubbed Proxima Centauri b.

Detecting planets at such distances is no easy task, said Wood-Vasey; Proxima Centauri is still more than 24 trillion miles distant. STEPUP uses a telescope that is not powerful enough to detect stars as more than a point of light; no star surface (if a star can even be said to have a surface) is visible. Planets crossing in front of their stars are thus detected by the amount of light they block from observers (about 1 percent) and the fact that each transit happens regularly, on a predictable and observable schedule, indicating an orbit.

STEPUP observers see no image of those transiting exoplanets. Instead, they gather data indicating a drop in the light output of a star as a planet crosses its edge, a stable amount of decreased light as the planet cruises across the body of the star, and then an increase in light back to the star’s known magnitude as the planet finishes its journey across the star’s face. Most transits last one-and-a-half to three hours, although some are longer and some less than an hour. “So we like to observe for twice that length of time,” Wood-Vasey said, to capture both the transit and the measurable light before and after it, for comparison.

Pittsburgh’s sky has lots of light pollution, so STEPUP observers are restricted to the brighter, or higher magnitude, stars. And they do all their observing remotely, controlling the Allegheny Observatory telescope, dome, computers and cameras from a room in Allen Hall that is crowded with 17 computer screens, a star atlas and posters celebrating planets already found: “Experience the gravity” of HD 40307g, “a super earth,” says one poster. “Relax on Kepler-16b,” a binary star system with a red star and a white star, “Where your shadow always has company,” says another.

At a recent meeting of the STEPUP team, Wood-Vasey quizzed a student about project progress while Allegheny Observatory manager Lou Coban added updates about equipment maintenance and software improvements.

Ian Cooper, a senior this year, told Wood-Vasey about the status of light-detecting software and debated adjusting the camera’s aperture to get the whole star surface. If the aperture is too wide, light from other stars begins to intrude; too narrow and not enough light is detected.

They discussed their choice of a reference star during observations — a star whose brightness has long been measured and determined to be steady, so that, if it dims while STEPUP researchers are trying to observe a transit (due to interference from Earth’s atmosphere), they will know that the dip in brightness they also observe in their target star is not necessarily due to an orbiting planet.

Star spots — analogous to sunspots — are the biggest contaminant of STEPUP data, since star spots also move across their suns. Anything close to Earth that moves across a star won’t be mistaken for a planet — it will simply be so large, relatively speaking, as to eclipse any star being observed.
Are certain types of stars more likely to have planets? “That is indeed one of the big questions people are pursuing,” Wood-Vasey said. Right now STEPUP is shifting to look at more binary star systems than single-sun systems like our own.

While most planets so far detected would not be easy for Earth life to inhabit, some of their moons may have potential for life, and moons may be detectable, since their orbits affect planet transits. “It would be really nice if we could find a moon around one of these planets,” he said — particularly one larger than our moon, which could hold an atmosphere.

“I started the summer with grand dreams,” Wood-Vasey told the group: that all the undergrads in STEPUP had a system to look at and, for the first time, all would publish a paper based on their observations. But too many cloudy or stormy nights have intervened, which is par for the course in Pittsburgh. “It’s always been a challenge for us, observing, because half the nights you can’t,” Wood-Vasey said. He still hopes his students can publish this fall.

“These types of observations teach the basics of astronomical observation,” Wood-Vasey explained. “Observations require not big telescopes but time, and time is one area where undergraduates can compete with professionals. My hope is that the group’s effort provides opportunities at Pitt” — opportunities for undergrads to do real research, and for them to develop their technical skills of observing and analysis, not to mention teamwork and research documentation.

Senior Cooper, who has been a member of the STEPUP team since 2014, said: “I really enjoy the idea of looking at the planets, the idea to look at other worlds that have the potential ….” He stopped himself. “I’m not going to say we’re going to find aliens here at STEPUP. But …. ”

It’s the larger telescopes, and those stationed in orbit, that are doing the even more technically sophisticated work of looking for new transits for groups like STEPUP to confirm, and of measuring the spectra of elements in planetary atmospheres to tell whether they might harbor life.

At the end of the STEPUP meeting, Wood-Vasey called out: “Does everyone have shirts?” The project has its own logo, with a planet transiting the Cathedral of Learning.

At Allegheny Observatory, inside one of the 30-foot domes, Lou Coban sat at a computer beneath the STEPUP’s 16-inch Meade reflecting telescope and commanded it to orient to Venus. He then told the dome to open, and its two doors slid to either side squeakily, creating a 6-foot-wide slit through which the telescope could point. Then he synced the dome to the telescope’s movements and it rotated once again along its bottom edge, aligning the opening with the telescope’s view.

The Meade telescope is a mere three feet long. “It is such a peanut in this dome,” Coban said — especially compared to the observatory’s 100-year-old, 47-foot-long, 30-inch refracting telescope, which looms above a visitor like an ocean-going ship hoisted into dry dock.

About four years ago, Coban and two Pitt students motorized the dome opening, which previously had to be turned by hand with a kind of ship’s wheel, which still sits propped against the dome wall.
Today, as the telescope rotates with the night sky, the dome also shifts position. It is capable of turning 360 degrees.

Another Pitt student, an undergraduate mechanical engineer, added a remotely controlled lens cap for the STEPUP students to use as well.

Coban sat at a quartet of screens on a small table beside the telescope’s arm and started Starry Night College 6, a commercial telescope-orienting program, and connected it to the telescope. Red crosshairs indicated where in the night sky the telescope is aiming.

Since all of STEPUP’s observations are of course at night — some are in the middle of the night — it’s good that no one has to be physically in the observatory, he said, although students must run each observation, and check on its progress, from Allen Hall.

“It works very well,” he reported. “It took a long time to get it like that. I’ve had to come over once or twice and I’ve had to kick it and push it,” he joked. Happily, he lives nearby.

Coban turned on the telescope’s main camera, its focuser and finder cameras and the lens cap control. The finder camera is external to the telescope, giving a lower-powered but wider view of the night sky to help orient it. The telescope points to coordinates in space, of course — no one is eyeballing the aim. But the finder camera can help if telescope users get lost or the target is not quite in focus.

The telescope’s main camera view is a tiny box on Coban’s computer screen within the much larger full-sky seen by the finder camera. And within the main camera view is an even smaller viewing guide chip. If users can get a guide star, such as the North Star, inside that much smaller box, that will be tracked throughout the night, helping keep the telescope centered on the actual star being observed, since everything in the sky rises and sets.

Coban turned on a controller that showed the four compass directions for aiming the telescope, plus different speeds for tracking stars. He used Starry Night to speed up a picture of the night sky, which spun in a dizzying circle, with the North Star in the tightest, tiniest circle at the center. In real time, to the naked eye, it appeared not to move at all — hence its use by sailors for navigation.

Outside, another camera is videotaping the weather, so that the STEPUP crew can log in and see local sky conditions during current and even past observations. They also can remotely check a clear-sky monitor — an infrared sensor measuring the temperature of the atmosphere, since warmer conditions can indicate cloudy skies. A third remotely accessible item outside, the “seeing” monitor, measures the steadiness of the atmosphere — how easy it is to see the stars. “You look up and you see the stars twinkling like crazy?” said Coban. “That’s a bad seeing night.” Pollution isn’t to blame, or credit, for the twinkling; instead, it’s radiational cooling — the heat rising from the ground — at work. Clear nights allow more radiational cooling, which interferes with telescope views.

Transparency — a measure of the clearness of the sky — in the atmosphere is best in winter, when the dew point is low and there is much less moisture in the air.

But winter is the worst for seeing. In the summer, the haze of the atmosphere tamps down turbulence.
When all the best atmospheric factors align, said Coban, “It only happens about 10 times a year – you can really see the constellations over the city of Pittsburgh.”

—Marty Levine 

Filed under: Feature,Volume 49 issue 1

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