Astronomers have new method of weighing solitary stars

Accurately estimating a star's mass is critical to determining the mass and size of planets orbiting it.
By Laurel Kornfeld | Dec 19, 2017
Astronomers have come up with a new method of weighing solitary stars, a development especially important for estimating the masses and sizes of exoplanets orbiting them.

The most common method used to determine stellar masses is geared toward binary or double star systems. Using Isaac Newton's laws of motion, scientists are able to compute the masses of both stars in a binary system by accurately measuring their orbits.

Calculating the masses of solitary stars, which constitute more than half of the Milky Way's star systems, has been more difficult, relying on less accurate methods such as photometry, which classifies stars by color and brightness, and asteroseismology, which relies on light fluctuations caused by sound pulses that move through stellar interiors.

While the latter method is more accurate than the former, it is useful only for the closest and brightest stars.

Now, researchers led by Keivan Stassun of Vanderbilt University's Department of Physics and Astronomy, have developed a new method of weighing individual stars specifically designed for the European Space Agency's (ESA) Gaia Mission, which is mapping the Milky Way in three dimensions.

"We have developed a novel method for 'weighing' solitary stars. First, we use the total light from the star and its parallax to infer its diameter. Next, we analyze the way in which the light from the star flickers, which provides us with a measure of its surface gravity. Then we combine the two to get the star's total mass," Stassun explained.

Parallax is a phenomenon in which a star's direction and/or position appears to differ when viewed from different positions.

This new method will also work well with NASA's upcoming Transiting Exoplanet Survey Satellite (TESS) mission, which will search for Earth-like planets around the 200,000 brightest stars once launched next year.

Four-fifths of red dwarf stars, which scientists think might pose the best chances for having Earth-like planets, are solitary rather than part of binary systems.

Several years ago, Stassun developed a method of determining a star's surface gravity based on subtle patterns of flickering in its light.

Last year, he followed up with a means of measuring a star's diameter by combining information on its temperature and luminosity with parallax data collected by the Gaia mission.

"By putting together these two techniques, we have shown that we can estimate the mass of stars cataloged by NASA's Kepler mission with an accuracy of about 25 percent, and we estimate that it will provide an accuracy of about ten percent for the types of stars the TESS mission will be targeting," he stated.

A report on the study has been accepted for publication in the Astronomical Journal.


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