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Jane Platt 818-354-0880
Jet Propulsion Laboratory, Pasadena, Calif.
Jane.platt@jpl.nasa.gov
NEWS RELEASE: 2008-016 Jan. 28, 2008
Linked Hawaiian Telescopes Catch a Nova Surprise
First results from a new NASA-funded scientific instrument at the W. M. Keck Observatory
at Mauna Kea, Hawaii, are helping scientists overturn long-standing assumptions about
powerful explosions called novae and have produced specific information about one nearby
nova.
This sophisticated new system, called the Keck Interferometer, combines the observing power
of the two 10-meter (33 feet) Keck telescopes into a single mega-telescope. Using the
interferometer's "nulling" mode, data were taken by the Keck Interferometer team on a nearby
nova called RS Ophiuchi.
In "nulling" mode, the Keck Interferometer suppresses the blinding light of a star so
researchers can study the surrounding environment. The instrument helps them observe very
faint objects near bright sources and produces 10 times more resolving power than a single
Keck telescope working alone. It is the only instrument of its kind in operation.
The nulling mode was developed to search for dust regions around nearby stars, where planets
might be forming, but the bright starlight poses a great challenge. "Because a star is so much
brighter than the dust, something has to block the light, which is what the nuller does," said
Rachel L. Akeson, Keck Interferometer project scientist at the California Institute of
Technology's Michelson Science Center. "This technique turns out to be useful for lots of
other kinds of objects, including this one, where dust is near a star that just went nova."
These nova data were taken by a team led by Wes Traub of NASA's Jet Propulsion
Laboratory, Pasadena, Calif., and the data analysis and unified model for the nova were
produced by a team led by Richard Barry and William Danchi of the Goddard Space Flight
Center, Greenbelt, Md.
The star in the constellation Ophiuchus went nova at the perfect time for the team, on Feb. 12,
2006. "We were extremely lucky, because we had astronomers in place at two mountain-top
interferometers, Keck in Hawaii and Infrared Optical Telescope Array in Arizona. Within
minutes of hearing about the discovery of the nova, we alerted both teams to start observing it
that night," said Traub, a senior research scientist at JPL.
The nova system, known as RS Oph 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. RS Oph was previously observed blowing its stack in 1898,
1933, 1958, 1967 and 1985, so astronomers were eagerly anticipating the 2006 eruption.
About three-and-a-half days after the nova was detected, the group observed the explosion
with the Keck nuller. They set the instrument to cancel the nova's light, allowing them to see
the much fainter surrounding material, and then 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 chemical 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 Goddard, lead author of the paper on
the observations that will appear in the Astrophysical Journal. The team thinks the dust is
created as the white dwarf plows through the red giant's wind, creating a pinwheel pattern of
higher-density regions that is reminiscent of galaxy spiral arms. Inside these arms, atoms
become cool enough and dense enough to allow atoms to stick together to form dust particles.
The nova's blast wave has since destroyed RS Oph's pinwheel pattern, but it should re-form
over the next few years, and future observations by NASA's Spitzer Space Telescope could
see it. Barry is also coauthor of a paper based on Spitzer observations of RS Oph.
Most studies of RS Oph have relied on spectroscopic models, which have not been able to
distinguish various nova components with as much detail as the interferometer. The Keck
nuller measured one component of the RS Oph system to an accuracy of just
4 milliarcseconds, or about the size of a basketball seen 7,500 miles away.
The Keck Interferometer is part of NASA's ongoing quest to search for planets orbiting other
stars. JPL, a division of Caltech, manages the Keck Interferometer for NASA. The Keck
Interferometer was developed by JPL, the W.M. Keck Observatory and the Michelson
Science Center. The W.M. Keck Observatory is funded by Caltech, the University of
California and NASA, and is managed by the California Association for Research in
Astronomy, Kamuela, Hawaii. More information on the Keck Interferometer is at
Additional contact: Laura Kinoshita/Keck Observatory, Mauna Kea, Hawaii:
877-239-3067 laura@laura-kinoshita.com
-end-
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