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A Double Astrono-Whammy of Exoplanet Finds November 13, 2008

Posted by Sarah in science.
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P. Kalas, UC Berkeley.

Image of the Fomalhaut debris disk with the image of Fomalhaut b inset. Image credit: P. Kalas, UC Berkeley.

National Research Council of Canada.

The HR8799 planetary system imaged with the Keck telescope. Image credit: National Research Council of Canada.

Since the detection of the first exoplanet in 1995, exoplanet astronomy has advanced in leaps and bounds. With well over 300 planets known to orbit stars other than the Sun, something special is needed for a discovery to hit the headlines. Today, two separate teams of astronomers are publishing results with a great big X-factor in the journal Science.

For the first time, astronomers have managed to produce images of planetary systems around other stars.

What about this, you ask? This image of the 2M1207 system, hailed as the first even exoplanet image on its release in 2005, is indeed an exoplanet image. But its host is a brown dwarf; a sub-stellar sized object that isn’t massive enough to burn fuel its core.

The first team of exoplanet searchers, led by Christian Marois of the Herzberg Institute of Astrophysics in Victoria, Canada, used the Gemini and Keck Telescopes with powerful adaptive optics systems to correct for image-blurring atmospheric turbulence to spot no fewer than 3 planetary companions around the star HR8799. Using a combination of high-contrast imaging and coronagraphy, where the light from the central star is blocked out with a mask, the team were able to establish that they were indeed co-moving with the star HR8799, and from their brightness inferred that they have a mass indicative of planets rather than brown dwarfs. While the planets show similarities with the 2M1207 system, it is set apart by the fact that the HR8799 is a real star not unlike our Sun.

The second exoplanet image, produced with the Hubble Space Telescope’s Advanced Camera for Surveys by a team led by Paul Kalas of UC Berkeley, is special as its host star is one of our nearest neighbours, Fomalhaut. Like many stars in our solar neighbourhood, bright star Fomalhaut is surrounded by a disk of dusty debris. Such disks are produced in the aftermath of star formation when smaller bodies around the star collide and break up into dusty rubble. Fomalhaut’s companion, Fomalhaut b, whose presence was confirmed with 6 independent HST observations over almost 2 years, is thought to be up to 3 Jupiter masses in size, orbiting at a distance of around 115 AU from the parent star. Interestingly, based on these figures, Fomalhaut b should be some 100 times fainter than was observed in the images. The researchers suggest that the excess in visible light from the planet may be due to an extensive ring system around the planet that is scattering and reflecting light.

Of the hundreds of known exoplanets, the majority were discovered using indirect detection methods, such as observing the wobble in a star’s motion caused by the tug of an exoplanet, or catching the dip in brightness of the star when a large planet passes in front of it. Obtaining a direct image of a planet is a very challenging task, with the starlight completely swamping the photons from its tiny faint companion. In a companion piece in this week’s edition of Science, Mark Marley discusses the techniques the astronomers used to obtain these fantastic images.

On a more personal note, as someone who helps design instruments to do this kind of work, it’s hard not to be blinded by the immense difficulties we face in collecting the light from these faintest of sourcs. I admit to being quite pessimistic about direct imaging of exoplanets. Every once in a while an image comes by that makes me sit up and realise that, WOW, this stuff actually WORKS! And today we got two of those.

We’re still a long way away from imaging other Earths in extrasolar systems, but if these new results are anything to go by, exoplanet research is definitely alive and kicking.

UPDATE, 14/11: Check out Discovery Space, which features an IM interview with Dr. Sara Seager, an expert on exoplanet research from MIT.


1. When you’ve seen one planet…. « In the Dark - November 14, 2008

[…] Well, actually, we knew that. We live on one. And anyway, the International Astronomical Union recently stipulated that planets could only be things orbiting the Sun.  Don’t ask me why. So the new things have to be called exoplanets. And over 300 hundred of these were known before today anyway.  A rose by any other name would smell as sweet, so we won’t worry about the taxonomy. But what’s the big deal? […]

2. SarahAskew » The benefit of hindsight - October 14, 2010

[…] interesting paper turned up on astro-ph last week. Remember HR8799, the star with a whole family of exoplanets imaged directly last year? A Canadian-American team of […]

3. SarahAskew » Super-earth confirmed, first of many? - October 14, 2010

[…] reported the discovery of 51 Peg b, has seen a number of “major breakthroughs” (see here, here, and many more) in the detection and characterisation of planets around other stars in our […]

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