Astronomer studies far-off worlds through 'characterization by proxy'

April 26, 2013 by Peter Kelley in Astronomy & Space / Astronomy



Ballard is lead author of a study accepted for publication in The Astrophysical Journal that used this method and observations from the Kepler to learn the nature of the Kepler-61.

Our understanding of the size and temperature of planets depends crucially on the size and temperature of the stars they orbit. Astronomers already have a robust way to discern the physical properties of solar-type stars—those like the sun—by measuring the light they emit at different wavelengths and matching that to synthetically created spectra.

"The challenge is that small stars are incredibly difficult to characterize," Ballard said. Those theoretical methods don't work well for what are called M-dwarf stars, lower-mass stars about half the size of the sun and smaller—which is too bad, because such stars make up about three-quarters of the universe.

Ballard is using the characterization by proxy method to try to fill this . She is building on what she calls "truly remarkable" work by astronomer Tabetha Boyajian, now at Yale University, who uses a near-infrared interferometer—an array of telescopes working in unison studying light wavelengths a bit longer than visible light—to resolve the physical size of relatively .


In the new paper, Ballard and co-authors used this reasoning to learn about Kepler-61b, a planet orbiting near the inner edge of the of the distant, low-mass star Kepler-61, about 900 light-years away in the Cygnus Constellation. A star's habitable zone is that swath of space just right for an orbiting planet's surface water to be in liquid form, thus giving life a chance.


A funny thing also happened along the way: Kepler-61 turned out to be bigger and hotter than expected, which in turn recalibrated planet -61b's relative size upward as well—meaning it, too, would be hotter than previously thought and no longer a resident of the star's habitable zone.

All of this caused Ballard to informally subtitle the paper, "How Nearby Bumped a Planet out of the Habitable Zone."

More information: iopscience.iop.org/0004-637X

Provided by University of Washington

"Astronomer studies far-off worlds through 'characterization by proxy'" April 26, 2013 http://phys.org/news/2013-04-astronomer-far-off-worlds-characterization-proxy.html