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No 58 - December 2008

Exoplanets come into view

As I was waiting for the No 41 bus, I watched two Nos 42 pass each other, and I thought to myself: "This is like exoplanets - first you wait for years for someone to take a picture of them, then three pictures turn up within a single month."

First off, at least in terms of page numbers in Science (Science Express of 2008-11-14, Science of 2008-11-28), is a US/Canadian team who used the Hubble Space Telescope to obtain visible-light coronagraph images of Fomalhaut, 25 light years away and brightest star in the constellation Piscis Austrinus. They find one planet of about 3 Jupiter masses 115 AU from the star. This is present in images from 2004 and 2006 and has moved during that interval. The coronagraph is needed to block out the 1000 million times brighter star.

Next up is a Canadian/US/Exeter team who find no less than three planets around HR 8799, a 6.0 mag star in Pegasus, 129 light years away and not really better known as BD+20 5278. This team used the 10-metre Keck and 8-metre Gemini telescopes in infrared, where adaptive optics are employed to make good use of the aperture superior to the Hubble. The three planets are 10, 10 and 7 Jupiter masses and at distances of 24, 38 and 68 AU from the star.

On 2008-11-21 the European Organisation for Astronomical Research in the Southern Hemisphere - formerly known as European Southern Observatory and still known as ESO - made a press release announcing a likely image of a planet around β Pictoris, 70 light years from Earth and well known to have a circumstellar disc. A French team used one of ESO's four 8-metre VLT telescopes, and again adaptive optics at infrared wavelengths was employed. This planet has 8 Jupiter masses, but at about 8 AU it is rather closer to the star than in the cases of Fomalhaut and HR 8799.

In all three cases, dust discs were known before the search for the planets began, and indeed detail in these discs had hinted at the presence of planets.

These were in fact not the first images of exoplanets. In 2004 the VLT had taken an image of 2M1207, 170 light years away. That was rather simpler to do, since the central object is not a star, but a brown dwarf only 100 times brighter than the planet. That planet is between 3 and 10 Jupiter masses and 40 AU from the brown dwarf. This object is at -40° declination and not visible from Scotland. The brown dwarf is 20 mag, well beyond most amateur telescopes, anyway.


Horst Meyerdierks


Cover page

IYA astro-happening at Science Festival

Johann von Lamont - Bavaria's Scottish Astronomer Royal

Never the TWAN shall meet?

Total eclipse of the sun on 1st August 2008

Forthcoming events

Exoplanets come into view

Recent observations

Variable star observing workshop

Society news

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