New Method More Accurately Measures Far-Off Worlds
April 26, 2013

Characterization By Proxy Advances Understanding Of Milky Way’s Stars

John P. Millis, Ph.D. for — Your Universe Online

One commonly used method in astronomy is to study spectra and light curves from stars and compare the data to known values, allowing researchers to derive information such as chemical composition, size, and surface temperature. The trouble with this method is it only works on stars that are bright enough or close enough to study in detail.

Unfortunately, this precludes nearly three-quarters of the stellar population, which is composed of small, cool, red-dwarf stars. This makes the majority of objects in our galaxy extremely difficult to study.

But researchers at The University of Washington are attempting to change that. The team, led by post-doctoral researcher Dr. Sarah Ballard, is taking advantage of near-infrared data of very nearby M-dwarf stars that has been used to determine, with high precision, their size. Her team then uses these data as standards against which they can measure similar M-dwarf stars that are considerably more distant and fill in the information gap.

Ballard and her team initially studied the star Kepler-61, which is about 900 light-years away in the constellation Cygnus, using data from the Kepler Space Telescope. They used four nearby M-dwarf stars that have similar spectral profiles; all of which are within 25 light-years of Earth.

What they found was Kepler-61 was bigger and hotter than previously thought. Interestingly, this had an effect on the planets that have been found orbiting the star. Kepler-61b, for instance, was believed to reside in the star´s habitable zone — the area within which life could possibly arise if the conditions on the planet are appropriate.

Now, however, the team determined the planet would also be much larger and hotter than had been previously reported, making it unfit for life. This led Ballard to subtitle her paper, “How Nearby Stars Bumped a Planet out of the Habitable Zone,” which has been submitted for publication in The Astrophysical Journal.

This method, known as Characterization by Proxy, has the potential to significantly advance our understanding of most of the Milky Way´s stars. As this is applied to the broader stellar census, we may find previous measurements of dwarf stars were insufficient, potentially impacting our understanding of the planets that orbit them as well.