Seeing into the heart of planetary systems
14-Apr-2010, Plain html version.
Royal Astronomical Society Press Release
RAS PN 10/34 (NAM 19)
April 12th 2010
Seeing into the heart of planetary systems
Using four of the world’s largest telescopes, scientists have obtained the most detailed information yet from the regions around two young stars tens of light years away, finding compact discs of rocky and dusty material at distances comparable to that from the Earth to the Sun. Keele University astronomer Dr Rachel Smith will present the team’s results on Wednesday 14th April at the RAS National Astronomy Meeting (NAM 2010) in Glasgow.
The astronomers used data from the MIDI interferometer, an instrument that combines the infrared light from the 8-m diameter telescopes of the European Southern Observatory’s Very Large Telescope in Chile to simulate the performance of a single telescope with a mirror more than 100 metres across.
Two of the stars observed with MIDI are similar to our Sun – one is a little cooler and one a little hotter. The first, catalogued as HD69830, is an orange star with spectral type K0V and is thought to be about 2 billion years old (compared with the Sun’s age of 4.5 billion years). It lies in the direction of the southern constellation of Puppis, is around 41 light years from the Sun and is known to have three planets with masses comparable to Neptune. The second star, eta Corvi (in the constellation of Corvus and 59 light years from the Sun) is spectral class F2V, equivalent to a yellow-white colour, and is about 1.3 billion years old. Earlier observations hinted at discs of material around both stars. Cold material was confirmed around eta Corvi as it lies 22.5 billion km from that star and so was easier to spot.
With MIDI the region of the relatively small dusty disc around HD69830 is clearly seen and lies between 7.5 and 360 million km from the star. If you were standing on the surface of one of its planets, this dust would be a spectacular sight, several thousand times brighter than the similar but much fainter zodiacal dust that can be seen from the Earth on a dark night.
One intriguing possibility for the source of the dust is that the planets around HD69830 are experiencing a high rate of impacts from asteroids and comets smashing into their surfaces. A similar disc is also found close in to eta Corvi, lying between 24 to 450 million km from its stellar host. For comparison the Earth is on average about 150 million km away from the Sun.
These results represent the first resolution of dusty discs so close in to their parent stars, observations made possible using an interferometer like MIDI. The ages of the two stars and the locations of the dusty disks suggests that they may either originate from the debris of recent collisions of massive objects or travel there from an outer, cooler disc like the one around eta Corvi.
Dr Smith sees this work as part of the overall quest to find Earth-like planets around other stars. “With MIDI we have access to a truly giant telescope that can see the Universe in unprecedented detail. By probing regions of a similar scale to the Earth’s orbit we have the potential to observe the dusty results of massive collisions in the final stages of rocky planet formation, and learn about the conditions Earth-like planets in other planetary systems may experience. The opportunities for directly testing our theories for how planets form and evolve have never been greater.”
Dr Rachel Smith
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IMAGES AND CAPTION
Images available from the password-protected site http://www.astro.gla.ac.uk/~iain/nam_temp/press/ username: nam2010, password: 67$%nam
The images can also be downloaded from http://www.astro.keele.ac.uk/~rs/
The star HD69830 observed in the mid-infrared on a single 8-m telescope. This image looks the same as the image of a star with no dust around it. Credit: ESO / Rachel Smith. Full size version
A star with no dust around is compared with HD69830 to confirm we do not see extended dust emission with a single telescope. Credit: ESO / Rachel Smith Full size version
When we subtract the image of a normal star from the image of HD69830 we can see very clearly that we cannot resolve the dust emission with a single telescope. Credit: ESO / Rachel Smith Full size version
When we combine the light from two 8-m telescopes with MIDI we can simulate the resolving power of a telescope with diameter of about 100m. These observations give a 'visibility function', which measures how resolved a source is: a visibility of 1 happens when a source is completely unresolved, lower visibilities indicate increased resolution. For HD69830 we do not resolve the star itself, but do resolve the dust emission, as the visibility clearly does not match the pattern of an unresolved source (dashed blue line). The levels of dust emission vary in the wavelength range covered in the observation (8-13um, a region of the mid-infrared spectral range) and this variation can also be seen in the visibility function.
These results and the imaging shown above show that the dust lies between 7.5 and 360 million km from the star (0.05-3 times the Earth-Sun distance). Credit: ESO / Rachel Smith Full size version
The results of this study are published in the journal Astronomy and Astrophysics. The paper can be seen at http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/full_html/2009/31/aa11626-09/aa11626-09.html
NOTES FOR EDITORS
RAS NATIONAL ASTRONOMY MEETING (NAM 2010)
The RAS National Astronomy Meeting 2010 will take place from 12-16th April at the University of Glasgow. The conference is held in conjunction with the UK Solar Physics (UKSP) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST) meetings. NAM2010 (www.astro.gla.ac.uk/nam2010/) is principally sponsored by the Royal Astronomical Society (RAS) and the University of Glasgow.
THE ROYAL ASTRONOMICAL SOCIETY
The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
THE UNIVERSITY OF GLASGOW
The University of Glasgow (founded 1451) is one of the world’s top 100 research universities with more than 70 per cent of its research rated as world-leading or internationally excellent. The Physics and Astronomy Department is one of the top four in the UK’s major research-intensive universities, the Russell Group.
The conference comes to Glasgow during the 250th anniversary year of the founding of the Regius Chair of Astronomy at the University of Glasgow, first held by astronomer and meteorologist Alexander Wilson in 1760. The present incumbent is Prof. John Brown, 10th Astronomer Royal for Scotland.