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Last Updated: Thursday, 3 July, 2003, 14:43 GMT 15:43 UK
First for Hawaiian telescope link-up
By Dr David Whitehouse
BBC News Online science editor

The first scientific result from a pair of linked telescopes - the mighty Keck twins on Mauna Kea - has been released. It is the observation of a young star surrounded by a disc of dust in which planets may be forming.

Artist's impression of DG Tau's dust disc

When the two 10-metre (33 feet) Kecks - sited up a volcano in Hawaii, US - open their eyes on the heavens in tandem, they form what is arguably the world's largest optical telescope system.

Acting in unison, they create an interferometer, in which the outputs from several smaller telescopes are combined to mimic that from a much larger, single telescope.

The swirling dust disc seen around the star DG Tau is an important discovery, say astronomers. Observations of such systems, now possible at higher resolution, will cast light on how worlds like our Earth formed.

Combining signals

Interferometry is a technique used routinely in radio astronomy where the long wavelengths involved make the bringing together of signals from different dishes relatively straightforward.

In the optical region of the spectrum, things are more difficult, however, because the shorter wavelengths involved demand a greater accuracy when combining the light beams.

Still under development, the Keck interferometer is equivalent to a single 85-metre (279 feet) telescope.

An added complication for engineers trying to bring the different light signals together is that the individual Keck telescopes employ an adaptive optics system. This adjusts the shape of the telescopes' mirrors to remove distortion caused by the Earth's atmosphere.

It all has to be taken into account to provide a final pin-sharp image.

Immature star

The Keck interferometer's inaugural scientific observation was of the young star DG Tau, a star that is not yet mature because it has not yet started to burn hydrogen in its core.

"We're trying to measure the size of the hot material in the dust disc around DG Tau, where planets may form," says Rachel Akeson, of the California Institute of Technology, in Pasadena, US.

"Studies like this teach us more about how stars form, either alone or in pairs, and how planets eventually form in discs around stars," she adds.

The observations reveal a gap of 29 million kilometres (18 million miles) between DG Tau and its orbiting dust disc.

This may be significant because the gap is larger than that seen in other systems. Of the planets known to orbit other stars, roughly one in four lies within 16 million km (10 million miles) of the parent star.

Because planets are believed to form within a dust disc, either DG Tau's disc has a larger-than-usual gap, or planets form farther out from a star and migrate inward.

By measuring dust around other stars where planets may form, the Keck interferometer will pave the way for the US space agency's Terrestrial Planet Finder mission which will look for Earth-like planets.




SEE ALSO:
Two become one: Giant telescopes linked
15 Mar 01  |  Science/Nature
Europe plans world's biggest telescope
05 Dec 02  |  Science/Nature
Six telescopes act as one
19 Mar 02  |  Science/Nature


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