NASA instrument observes nova explosion

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Washington, Jan 29 : Scientists have observed a nearby nova called RS Ophiuchi with the help of a NASA-funded instrument at the W.M. Keck Observatory in Hawaii. Novas are powerful cosmic explosions caused by the accretion of hydrogen onto the surface of a white dwarf star.

"We were getting ready for a routine engineering run when all of a sudden the nova went off. It was very bright and easy to observe," said team member Marc Kuchner of NASA's Goddard Space Flight Center in Greenbelt, Maryland, US. Kuchner and his colleagues used the "nulling" mode of the Keck Interferometer, which is part of the NASA-funded Keck Interferometer for the observation. This instrument combines starlight using two 10-meter (33 feet) telescopes.

In the nulling mode, the interferometer suppresses the blinding light of a star so researchers can study the surrounding environment. The instrument helps researchers observe very faint objects near bright sources and produces ten times more resolving power than a single Keck telescope working alone.

The Keck Nuller was undergoing tests on February 12, 2006, when a nova flared up in the constellation Ophiuchus.

The system, known as RS Ophiuchi, consists of a white dwarf and a red giant. The red giant is gradually shedding its massive gaseous outer layers, and the white dwarf is sweeping up much of this wind, growing in mass over time.

As the matter builds up on the white dwarf's surface, it eventually reaches a critical temperature that ignites a thermonuclear explosion that causes the system to brighten 600-fold.

Just 3.8 days after the nova was detected, the group observed the explosion with the Keck Nuller. The team set the instrument to cancel out the nova's light, allowing the group to see the much fainter surrounding material. The group next adjusted the nuller to observe the extremely bright blast zone.

The instrument's versatility was key to a surprising discovery.

The nuller saw no dust in the bright zone, presumably because the nova's blast wave vaporized dust particles.

But farther from the white dwarf, at distances starting around 20 times the Earth-Sun distance, the nuller recorded the spectral signature of silicate dust. The blast wave had not yet reached this zone, so the dust must have pre-dated the explosion.

"This flies in the face of what we expected. Astronomers had previously thought that nova explosions actually create dust," said Richard Barry of NASA Goddard, lead author of a paper on the Keck observations.

"The RS Ophiuchi observations are just a small taste of the power and potential we expect from the Keck Nuller," said coauthor William Danchi of NASA Goddard.

"But ultimately we want to launch a nulling interferometer into space to image extrasolar planets. These Keck results are a technological and scientific pathfinder toward that future," he added.


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