Astronomers observe a star in the making

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Munich, Jan 30 : Astronomers at European Southern Observatory (ESO) have used the VLT (Very Large Telescope) Interferometer to probe the inner parts of the disc of material surrounding a young star, witnessing how it gains its mass before becoming an adult.

The object, known as MWC 147, is located in the constellation of Monoceros, which is about 2,600 light years away from Earth.

MWC 147 belongs to the family of Herbig Ae/Be objects. These have a few times the mass of our Sun and are still forming, increasing in mass by swallowing material present in a surrounding disc.

According to ESO, this stellar object is less than half a million years old. Compared with the 4.6 billion year old sun, MWC 17 is quite young.

The observations of the object was made by astronomers Stefan Kraus, Thomas Preibisch, and Keiichi Ohnaka, who used the four 8.2-m Unit Telescopes of ESO's VLT for this purpose, combining the light from two or three telescopes with the MIDI and AMBER instruments.

"Different wavelength regimes trace different temperatures, allowing us to probe the disc's geometry on the smaller scale, but also to constrain how the temperature changes with the distance from the star," said Stefan Kraus, lead author of the paper.

The near-infrared observations probe hot material with temperatures of up to a few thousand degrees in the innermost disc regions, while the mid-infrared observations trace cooler dust further out in the disc.

The observations show that the temperature changes with radius are much steeper than predicted by the currently favoured models, indicating that most of the near-infrared emission emerges from hot material located very close to the star, that is, within one or two times the Earth-Sun distance (1-2 AU).

This also implies that dust cannot exist so close to the star, since the strong energy radiated by the star heats and ultimately destroys the dust grains.

According to Kraus, "We have performed detailed numerical simulations to understand these observations and reached the conclusion that we observe not only the outer dust disc, but also measure strong emission from a hot inner gaseous disc. This suggests that the disc is not a passive one, simply reprocessing the light from the star."

"Instead, the disc is active, and we see the material, which is just transported from the outer disc parts towards the forming star," he added.


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