New Collaboration Bags First Planet

by Paul Gilster on May 20, 2006

One of the most exciting things about the exoplanet hunt is that it isn’t confined to huge observatories, nor does it demand bankrolling by billionaires. Consider the news that a team of professional and amateur astronomers has collaborated on a new planetary find, using off-the-shelf equipment and modest telescopes. The Jupiter-sized world orbits a Sun-like star some 600 light years away in the constellation Corona Borealis. The work is significant not just for the planet it discovered but for its implications for future collaborative work.

Four amateurs worked with Peter McCullough of the Space Telescope Science Institute (Baltimore) to nail down the discovery. McCullough used a 200-millimeter telephoto camera lens mounted on an inexpensive device called the XO telescope on the summit of the Haleakala volcano in Hawaii (total cost for the equipment: roughly $60,000), while the amateurs contributed their own telescopes.

Here’s the search method: McCullough’s XO telescope makes nightly sweeps and feeds data to a computer that analyzes starlight looking for the dips that might indicate a transit. Out of tens of thousands of observed stars, the few hundred possibilities considered the most interesting are pared to several dozen and then passed along to the four amateur astronomers for detailed study.

McCullough describes the recent find this way:

“It was a wonderful feeling because the team had worked for three years to find this one planet. The discovery represents a few bytes out of nearly a terabyte of data: It’s like trying to distill gold out of seawater.”

We’re dealing with a planetary transit here, signaled by a dip in the star’s light output as the planet crosses between it and the Earth. The observations were also good enough to peg the planet’s rotational period at four days. Centauri Dreams is jazzed not only by the discovery itself but by the boost the work gives to transitsearch.org, which champions the use of data from amateurs and small observatories. In the hands of exoplanet hunter Greg Laughlin (UC-Santa Cruz), transitsearch is continuing to build a collaborative network for such analysis, concentrating on known planet-bearing stars.

Be aware that this is only the 10th planet detected using transit methods. Throw that in with the inexpensive means used and you can see that transit hunting holds rich possibilities for future work. This discovery went on to be confirmed at the University of Texas’ McDonald Observatory, which was able to make a radial velocity measurement that allowed the calculation of the planet’s mass, finding it to be slightly less than that of Jupiter.

Up next may be Spitzer studies that could observe the infrared radiation from this planet and measure the eccentricity of its orbit. Still to be determined, among many other things, is an answer to the riddle of why this object’s diameter seems too large for a body of its calculated mass. And who knows, close observation of the planet may also help reveal the existence of others as they affect its orbit. But that’s for the future. Right now let’s celebrate the new kind of collaboration that is sure to bring in many more transit detections in coming years.

The paper on this work is McCullough, Stys, Valenti et al., “A Transiting Planet of a Sun-like Star,” accepted for publication in the Astrophysical Journal, and now available here (PDF warning).

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