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Planet finders use much faster instrument to discover distant planet(Forwarded)



 
 
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Old January 13th 06, 01:32 AM posted to sci.astro
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Default Planet finders use much faster instrument to discover distant planet(Forwarded)

News Bureau
University of Florida

Contact:

Writer: Aaron Hoover, (352) 392-0186
Source: Jian Ge, (352) 246-1398

Wednesday, January 11, 2006

Planet finders use much faster instrument to discover distant planet

GAINESVILLE, Fla. -- Astronomers have discovered a planet orbiting a
very young star nearly 100 light years away using a relatively small,
publicly accessible telescope turbocharged with a new planet-finding
instrument.

The feat suggests that astronomers have found a way to dramatically
accelerate the pace of the hunt for planets outside our solar system.

"In the last two decades, astronomers have searched about 3,000 stars
for new planets," said Jian Ge, a professor of astronomy at the
University of Florida. "Our success with this new instrument shows that
we will soon be able to search stars much more quickly and cheaply --
perhaps as many as a couple of hundred thousand stars in the next two
decades."

Ge and colleagues at the University of Florida, Tennessee State
University, the Institute of Astrophysics in Spain's Canary Islands,
Pennsylvania State University and the University of Texas presented
their findings today at the American Astronomical Society's annual
meeting in Washington, D.C.

Their work is important in part because of what the astronomers found --
a planet, at least half as massive as Jupiter, orbiting a star just 600
million years old. That's very young compared, for example, with the
sun's 5 billion years.

"This is one of the youngest stars ever identified with a planetary
companion," Ge said. Perhaps more significant, the instrument used to
find the planet points the way to a much more accessible method for
finding others -- including those capable of supporting life.

Planets outside our solar system are typically swamped by the light of
their stars, making it difficult to observe them visually. In the 1990s,
astronomers began using a measurement technique called Doppler radial
velocity to detect planets by observing the wobble in a star that is
gravitationally induced by an orbiting planet.

This technique, which has uncovered the vast majority of the 160-plus
extrasolar planets found so far, works by hunting through the spectrum
of starlight for the subtle Doppler shifts that occur as the star and
planet move toward and away from their common center of mass. The
instrument at the heart of this technique is usually a spectrograph, but
this instrument is problematic.

"A major problem with spectrographs is that they collect only a small
percentage of photons from the target light source, which means that
they are only useful to search for distant planets when mounted on
relatively large telescopes," Ge said.

The astronomers' new instrument, the Exoplanet Tracker, or ET,
eliminates this problem by swapping the spectrograph with an
interferometer, a device that can take more precise radial velocity
measurements. Tests show the interferometer can capture as much as 20
percent of available photons, making the instrument far more powerful,
which opens its use for distant planet hunting to smaller telescopes.

At a development cost of about $200,000, the interferometer-equipped ET
is also far cheaper than comparable spectrographs, which cost more than
$1 million. And at about 4 feet long, 2 feet wide and weighing about 150
pounds, it is lighter and smaller. The instrument is based on a concept
first proposed in 1997 by Lawrence Livermore National Lab physicist
David Erskine.

The astronomers used the Exoplanet Tracker on the special 0.9-meter
Coudé feed system within the National Science Foundation's 2.1-meter
telescope at Kitt Peak National Observatory near Tucson, Ariz.

Like radial velocity instruments equipped with spectrographs, the ET
instrument in its present form can search only one object at a time. But
Ge's team has demonstrated that it can hunt for planets around multiple
stars simultaneously -- a key element of its heightened utility. The
team is working on a version capable of surveying as many as 100 stars
simultaneously.

The Exoplanet Tracker will be used next spring for a trial planet survey
on the Sloan Digital Sky Survey 2.5 meter wide-field telescope at the
Apache Point Observatory in New Mexico. The new instrument is funded
with an $875,000 grant from the W.M. Keck Foundation. A much more
ambitious, long-term survey is in the planning stages.

The Kitt Peak Coudé feed telescope that Ge and colleagues used to
discover the new planet has a 0.9-meter mirror on a tall tower, a mirror
that directs incoming starlight into an observing room in the base of
the 2.1-meter telescope. The standard spectrograph in the facility fills
the room -- while ET occupies a small corner.

The new planet is the most distant ever found using the Doppler
technique with a telescope mirror less than 1 meter in size. There are
hundreds of such telescopes worldwide, compared with just a handful of
the larger 2- and 3-meter telescopes more commonly used in planet
finding -- telescopes that tend to be in extremely high demand and
difficult to access.

"These smaller telescopes are relatively cheap and relatively
available," Ge said, "so you can often get access to many dozens of
nights on them if you have a promising proposal."

Kitt Peak National Observatory is part of the National Optical Astronomy
Observatory, Tucson, Ariz., which is operated by the Association of
Universities for Research in Astronomy Inc., under a cooperative
agreement with the National Science Foundation.

"This is the first time that a planet has been discovered using a
publicly funded telescope at the U.S. national observatory," said Buell
Jannuzi, acting director of Kitt Peak National Observatory. "We are very
excited that the broader community of astronomers around the world will
be able to propose to use the single-object Exoplanet Tracker instrument
at Kitt Peak to carry out their own research programs, starting in the
fall of 2006."

That said, discovering new planets is never easy.

In the latest find, astronomers went to great lengths to ensure they
were actually "seeing" a planet. That's because the star, which has
about 80 percent of the mass of our sun, retains much of its youthful
rotation speed, which makes it capable of generating strong magnetic
fields and associated dark star spots. These are similar to the
magnetically generated sunspots on our own sun, and they can mimic the
presence of a planet in orbit around the star.

To check against this possibility, Greg Henry, an astronomer at
Tennessee State, observed the star with an automated telescope in
Arizona, and found the star to be changing its brightness as it rotates.

"My observations reveal a rotation period of about 12 days for the
star," Henry said. "Thus, if the planetary orbital period is indeed less
than five days, the dark spots rotating around on the surface of the
star every 12 days cannot be causing the false appearance of a planet."

Located in the direction of the constellation Virgo, the newly
discovered planet completes its orbit in less than five days, meaning it
orbits very close to its parent star and is very hot. That means it's
too close to the star to lie within the "habitable zone" where life is
possible.

[NOTE: An image supporting this release is available at
http://www.noao.edu/outreach/press/pr06/ir0601.html ]
 




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