By Patricia Daukantas
Astronomers are tracking down a stellar mystery, but they still need your help!
As I wrote in the March 2009 issue of OPN, a binary star known as Epsilon Aurigae is undergoing a two-year eclipse cycle, and astronomers don’t fully understand the nature of the objects.
A binary star consists of two stars that orbit their common center of mass. If a binary system is close enough to us and its components are bright enough, we can see both of them. In other cases, we have to rely on indirect evidence, such as periodic dimming caused when one star eclipses the other.
Auriga, a Northern Hemisphere constellation, is that roughly pentagon-shaped group of stars that includes the bright star Capella. Epsilon Aurigae – some 2,000 light-years from us – is one of the three stars that make up a small triangle near Capella, and its roughly two-year-long eclipse began in the summer of 2009. (The eclipses happen every 27.1 years, and detector technology has improved a lot over that time period.)
At the recent Washington, D.C. (U.S.A.) meeting of the American Astronomical Society (AAS), scientists who have been looking at Epsilon Aurigae through NASA’s infrared Spitzer Space Telescope outlined a possible explanation for the behavior of the binary system. To Donald Hoard of the California Institute of Technology, the brighter half of the pair may be a dying star, with two or three times the mass of the Sun, that is sometimes eclipsed by a single star inside a disk. This contradicts a different hypothesis that says the brighter star is something called an “F supergiant,” 20 times as massive as our Sun. The infrared data also suggest that the disk, if it exists, is unusually deficient in small dust grains (the size of smoke particles) and higher in grains the size of sand.
How can you help figure out what’s going on over there? The Web site CitizenSky.org is a clearinghouse of information about Epsilon Aurigae itself and about what you need to collect meaningful observations, whether or not you have a telescope. The “Dr. Bob” on this Web site is University of Denver (Colorado, U.S.A.) astronomer Robert Stencel, whom I interviewed for last year’s OPN article along with the dedicated amateur astronomer Jeff Hopkins.
In fact, several high school and college students, along with their instructors, got to present their observational data at a poster session at the AAS meeting. Physics and astronomy professor Darryl Stanford of the two-year College of San Mateo (California, U.S.A.) and seven undergraduates have been using the college’s 8-inch Meade Schmidt-Cassegrain telescope outfitted with a self-guided spectrograph that gets 2.4-angstrom resolution. Sally Seebode, a science teacher at nearby San Mateo High School, and two of her students also participate in the measurement of prominent absorption lines in the spectrum of Epsilon Aurigae.
The Epsilon Aurigae project shows that so-called “classical” astronomy is alive and well, both for citizen scientists and for educational institutions with moderate-sized telescopes, said Arne Henden, president of the American Association of Variable Star Observers. Bright-star observing campaigns provide an opportunity to engage the public in science.