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Star's twinkle may help reveal exoplanets' size

Washington, August 23 : Astronomers have devised a new way that slices and dices the flickering light from a distant star to determine the strength of gravity at its surface.


The new technique can also be used to significantly improve estimates of the sizes of the hundreds of exoplanets that have been discovered in the last 20 years.

The technique was developed by a team of astronomers headed by Vanderbilt Professor of Physics and Astronomy Keivan Stassun.

According to Stassun, once you know a star's surface gravity then you only need one other measurement, its temperature, which is pretty easy to obtain, to determine its mass, size and other important physical properties.

There are three traditional methods for estimating a star's surface gravity: photometric, spectroscopic and asteroseismic. The new flicker method is simpler than the older methods and more accurate than all but one of them.

Asteroseismology is the gold standard, with accuracies of a few percent, but the measurements are even more difficult to make than spectroscopy and it is restricted to several hundred of the closest, brightest stars. The technique traces sound pulses that travel through the interior of a star at specific frequencies that are tied to its surface gravities. Small stars, like the Sun, ring at a higher pitch while giant stars ring a lower pitch.

The new flicker method looks at variations in the star's brightness, In this case it zeroes in on variations that last eight hours or less. These variations appear to be linked to granulation, the network of small cells that cover the surface of a star that are caused by columns of gas rising from the interior. On stars with high surface gravity, the granulation is finer and flickers at a higher frequency. On stars with low surface gravity, the granulation is coarser and they flicker at a lower frequency.

The new method requires only five lines of computer code to make the basic measurement, which substantially reduces the cost and effort required to calculate the surface gravities of thousands of stars.

After conducting an experiment, researchers found that it has an uncertainty of less than 25 percent, which is better than both the photometric and spectroscopic methods.

The study has been published in the journal Nature.

--ANI (Posted on 23-08-2013)

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