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Supergiant star gains
thick dusty waist

DR EMILY BALDWIN
ASTRONOMY NOW
Posted: 28 January 2011


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Astronomers using ESO's Very Large Telescope (VLT) have spied a hot supergiant star on the verge of death that is sporting a thick, dusty waist band usually only associated with young stars.

Florentin Millour from Observatoire de la Cote d’Azur and Anthony Meilland from Max Planck Institute for Radio Astronomy used the VLT's interferometer to generate the first three-dimensional, high angular and high spectral resolution image of the star, HD 62623, and its nearby environment, providing evidence for the rotation of the gas around the central star. HD 62623 is located 2,100 light years away.


Images of HD 62623, obtained with the VLTI (left), compared to the model of a rotating disc (right). Gas motions are shown in the insets – blue-coloured gas approaches the observer, while red-coloured gas is moving away. The inner boundary of the gas disc is located 1.3 AU from the star and stretches to 4AU. Image: F. Millour et al.

Hot supergiants would normally emit a strong stellar wind that would prevent matter condensing as dust next to the star, but Millour and Meilland think a solar-mass companion star might by gravitationally grabbing HD 62623's mass and swirling it into a disc around the two stars.

"The companion star is probably located inside the gas disc, very close to the main star," Millour tells Astronomy Now, who adds that if compared to our own Solar System, the companion star is located inside the Earth's orbit. "If it were located further away, it would produce deformations to the disc that we would be able to detect, and we do not detect it."

The configuration bears some resemblance to the epsilon Aurigae system, although there the two stars are separated by a greater distance and so it is the companion star that hosts the disc. In HD 62623 the disc surrounds the binary system. "Technically speaking, we talk about a circumsecondary disc for epsilon Aurigae, and a circumbinary disc for HD 62623," says Millour.


The likely fate of HD 62623? This is the aftermath of supernova 1987A – a shock wave of material unleashed in the blast slammed into a ring of debris likely shed by the star 20,000 years previously. Image: NASA, ESA, P. Challis and R. Kirshner (Harvard-Smithsonian Center for Astrophysics)

As for the fate of this system, HD 62623 has only 10-20 million years left before it will exhaust its fuel supply and explode in a supernova event, likely blasting the companion star and their dust disc clean out of the system.

"The torn-off disc will create a drag in the equatorial region of the explosion and it will likely result in the formation of a bright ring and a bipolar ejecta, pretty much like the ones seen today in SN1987A," says Millour.

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