A better tool for more accurate planet hunting

The new calibration tool should allow for more accurate detection of exoplanets, an example of which is pictured here as an artist's impression(Credit: NASA/AMES/JPL-CALTECH)

A new calibration tool developed by researchers at the Carnegie Institute is set to have a big impact in the hunt for exoplanets. The technology allows astronomers to use a longer wavelength of light when analyzing distant stars, making it possible to pick out false positives in results.

While it's obvious that a planet is influenced by the gravity of its parent star, the relationship actually goes two ways, with the orbiting body also exerting a small influence of the star. The effect is, as you might expect, far more subtle, manifesting itself as a tiny shake or wobble induced as the planet tugs on the star.

Known as the radial velocity method, astronomers have used that little shake to pick out hundreds of exoplanets across the night sky, but it's not an entirely foolproof means of detection. In the case of certain low-mass stars, looking at that wobble may well indicate the presence of a planet, but other things can also cause the phenomenon, meaning that false positives can creep into results.

To fix the accuracy problem, the Carnegie Institute researchers decided to switch from visible to infrared wavelengths when making measurements. The wobble effect remains the same when observing in near-infrared as with visible light, but scientists can ascertain more from the data, picking out false positives caused by phenomena such as sunspots. Such things look the same as a planet in visible light, but are distinct at infrared wavelengths.

While infrared radial velocity measurements have been made before, the new calibration tool developed by the team significantly improves things, removing technological issues that have made visible light readings the preferred option until now.

They used the updated tool to study 32 low-mass stars with the NASA Infrared Telescope Facility located at the top of Mauna Kea in Hawaii. The results correlated well with existing confirmed data on the targets, identifying several planets and binary systems. Additionally, several new planerary candidates were identified.

"Our results indicate that this planet-hunting tool is precise and should be a part of the mix of approaches used by astronomers going forward," said researcher Peter Gao. "It's amazing to think that two decades ago we'd only just confirmed exoplanets actually existed and now we're able to refine and improve those methods for further discoveries."

Full details of the work are published online in The Astrophysical Journal.

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