ESO’s Very Large Telescope Interferometer (VLTI) at Paranal Observatory, Chile, has taken the sharpest image ever seen of the disc of gas and dust around an old star.
The dusty ring around IRAS 08544-4431: the inset shows the VLTI reconstructed image, with the brighter central star removed; the background view shows the surroundings of this binary star in the constellation of Vela. Image credit: ESO / Digitized Sky Survey 2 / Davide De Martin.
Although there are many dusty discs associated with infant stars that are sufficiently near to us to be studied in depth, there are no corresponding old stars with discs that are close enough for us to obtain detailed images.
But this has now changed — an international team of scientists, led by Dr. Michel Hillen of KU Leuven in Belgium, has used the power of the VLTI telescope, armed with several instruments.
Their target was IRAS 08544-4431, an old binary star located in the southern constellation of Vela, approximately 4,000 light-years away.
Also known as V390 Velorum, this binary consists of a red giant star, which expelled the material in the surrounding dusty disc, and a less-evolved more normal star orbiting close to it.
“By combining light from several instruments of the VLTI, we obtained an image of stunning sharpness – equivalent to what a telescope with a diameter of 150 m would see,” said team member Dr. Jacques Kluska, of Exeter University, UK.
“The resolution is so high that, for comparison, we could determine the size and shape of a one euro coin seen from a distance of 2,000 km.”
Thanks to the unprecedented sharpness of the VLTI images, the team could dissect all the building blocks of the IRAS 08544-4431 binary system for the first time.
The most prominent feature of the image is the clearly resolved ring. The inner edge of the dust ring, seen for the first time in these observations, corresponds very well with the expected start of the dusty disc: closer to the stars, the dust would evaporate in the fierce radiation from the stars.
“We were also surprised to find a fainter glow that is probably coming from a small accretion disc around the companion star,” Dr. Hillen said.
“We knew the star was double, but weren’t expecting to see the companion directly.”
The astronomers find that discs around old stars are indeed very similar to the planet-forming ones around young stars.
Whether a second crop of planets can really form around these old stars is yet to be determined, but it is an intriguing possibility.
“Our observations and modeling open a new window to study the physics of these discs, as well as stellar evolution in double stars,” said team member Dr. Hans Van Winckel, also from KU Leuven.
The results were published online in the March 9 issue of the journal Astronomy & Astrophysics.
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M. Hillen et al. 2016. Imaging the dust sublimation front of a circumbinary disk. A&A 588, L1; doi: 10.1051/0004-6361/201628125
