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On the trail of a disk around a star
vendredi 17 juin 2011

It is the clearest image ever taken in the near infrared of the inner part of a disk made of gas and dust surrounding a newly formed star. It has been obtained by a team of researchers, led by astronomers at INAF, using the technique of interferometry with the telescopes of the Very Large Telescope and the AMBER instrument.

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Images of the interior of the disk around the star HR5999
Reconstructed image of the interior of the disk around the star HR5999 at a wavelength of 2.2 microns (left) and model of the star-disk system (right). For clarity, the axis scales are shown in linear scale (1 AU is the Earth-Sun distance). The disc is tilted with respect to the line of sight, so it is possible to observe the inner edge, whose emission is produced by thermal radiation of dust heated by the star central star . The excellent correspondence between the image and the model is apparent.

In the near infrared, it is the clearest view ever obtained of the inner region of a disk of gas and dust surrounding a ’young’ star. This disk corresponds to the matter from which the star was formed, a structure that could create planets in the future, like our Solar System more than four billion years ago. This image was obtained after a long and complex process which involved a team of scientists led by researchers at the Astrophysical Observatory of Arcetri of INAF. To get to the result, two years of observations, processing of specific software and verification of results were necessary.

"The resulting image clearly shows a newly formed stellar system," said Fabrizio Massi from Arcetri Astrophysical Observatory who, together with Antonella Natta and Myriam Benisty, is part of the team that conducted the study of HR5999, published online today in the Astronomy & Astrophysics journal. "We believe that the system which is about 500,000 year old, give us a representation of what could have been our Solar System initially".

"Although we are very pleased with these results, we are working to improve the image reconstruction process to obtain, for example, direct evidence of planet formation in circumstellar disks such as the one around HR 5999." said Massi.

Young stars such as HR 5999 are in fact surrounded by a disk of gas and dust, residuals from the process that led to their formation. It is believed that planetary systems are created from this disk, in a region that is very difficult to study. Its typical size is roughly at the scale of the distance between the Earth and the Sun : about 150 million kilometers. But at 700 light years from us, where HR 5999 is located, to obtain an image of this region requires the same accuracy as needed to see a one-Euro coin from a distance of 1000 km. A single telescope, even the largest, is unable to observe such sharp details. But this level of details can be greatly increased by combining the light of the object collected by several separated telescopes, that is, by using interferometry. Through a complex mathematical algorithm that combines data from many different combinations of positions of the telescopes, it is possible to reconstruct an image of the object.

To achieve this technique, the team of scientists used the AMBER instrument, built by a Franco-German-Italian consortium in which the INAF-Arcetri Astrophysical Observatory has had a major part, building about a quarter of the instrument . AMBER can combine the light from three telescopes among the eight telescopes (four 8 m and four 1.8 m ones) of the ’ESO’ Very Large Telescope Interferometer in the Chilean Andes. With this method of observation, it is possible to obtain images with much higher angular resolution than the one allowed by any single optical telescope available, up to a level of details of the order of a thousandth of an arcsecond : by comparison, about forty times more accurate than those produced by the Hubble Space Telescope, and the same one that could only be produced by a telescope with a primary mirror of 140 m diameter.

Traduced and adapted from an INAF press-release. Paper published in Astronomy & Astrophysics, 531, A84 (2011).

Contact : Fabrizio Massi, INAF Arcetri.

More information
- press release at INAF
- paper freely available at A&A

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