VLT-Interferometer untersucht Exoplaneten

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Na, wenn das keine Sensation ist, die erste direkte Untersuchung eines Exoplaneten mit den vier interferometrisch gekoppelten 8-Meter Teleskopen des VLT:

First direct detection of an exoplanet by optical interferometry - Astrometry and K-band spectroscopy of HR 8799 e

To date, infrared interferometry at best achieved contrast ratios of a few times 10^−4 on bright targets. GRAVITY, with its dual-field mode, is now capable of high contrast observations, enabling the direct observation of exoplanets. We demonstrate the technique on HR 8799, a young planetary system composed of four known giant exoplanets. We used the GRAVITY fringe tracker to lock the fringes on the central star, and integrated off-axis on the HR 8799 e planet situated at 390 mas from the star. Our results demonstrate the power of interferometry for the direct detection and spectroscopic study of exoplanets at close angular separations from their stars.

Aus früheren Untersuchungen mit adaptiver Optik am Keck- und Gemini-Observatorium weiß man bereits, dass der Stern HR 8799 vier riesige Planeten besitzt. Der innere mit der Bezeichnung HR 8799e in einem Abstand von 15 AU wurde jetzt mit dem GRAVITY Interferometer am VLT unter die Lupe genommen. Dabei konnte erstmals das Spektrum der Planetenatmosphäre erfasst werden. Dabei fand man überraschenderweise nicht Methan, sondern stattdessen Kohlenmonoxid.

GRAVITY instrument breaks new ground in exoplanet imaging

This is the first time that optical interferometry has been used to reveal details of an exoplanet, and the new technique furnished an exquisitely detailed spectrum of unprecedented quality - ten times more detailed than earlier observations. The team's measurements were able to reveal the composition of HR8799e's atmosphere - which contained some surprises.

"Our analysis showed that HR8799e has an atmosphere containing far more carbon monoxide than methane - something not expected from equilibrium chemistry," explains team leader Sylvestre Lacour researcher CNRS at the Observatoire de Paris-PSL and the Max Planck Institute for Extraterrestrial Physics. "We can best explain this surprising result with high vertical winds within the atmosphere preventing the carbon monoxide from reacting with hydrogen to form methane."

The team found that the atmosphere also contains clouds of iron and silicate dust. When combined with the excess of carbon monoxide, this suggests that HR8799e's atmosphere is engaged in an enormous and violent storm.
 
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