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MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov 

Jane Platt  (818) 354-0880
Jet Propulsion Laboratory, Pasadena, Calif.

William Steigerwald  (301) 286-5017
Goddard Space Flight Center, Greenbelt, Md.

NEWS RELEASE: 2003-072      May 20, 2003

Newly-Discovered Star may be Third-Closest

The local celestial neighborhood just got more crowded with a
discovery of a star that may be the third closest to the Sun. The
star, "SO25300.5+165258," is a faint red dwarf star estimated to be
about 7.8 light-years from Earth in the direction of the
constellation Aries.

"Our new stellar neighbor is a pleasant surprise, since we weren't
looking for it," said Dr. Bonnard Teegarden, an astrophysicist at
NASA's Goddard Space Flight Center, Greenbelt, Md. Teegarden is lead
author of a paper announcing the discovery to be published by the
Astrophysical Journal. This work has been done in close collaboration
with Dr. Steven Pravdo of NASA's Jet Propulsion Laboratory, Pasadena,
Calif.  

If its estimate of distance is confirmed, the newfound star will be
the Sun's third-closest stellar neighbor, slightly farther than the
Alpha Centauri system, actually a group of three stars a bit more
than four light-years away, and Barnard's star, about six light-years
away. One light-year is almost six trillion miles, or nearly 9.5
trillion kilometers.

The new star has only about seven percent of the mass of the Sun, and
it is 300,000 times fainter. The star's feeble glow is the reason why
it has not been seen until now, despite being relatively close.

"We discovered this star in September 2002 while searching for white
dwarf stars in an unrelated program," said Teegarden. The team was
looking for white dwarf stars that move rapidly across the sky.
Celestial objects with apparent rapid motion are called High Proper
Motion objects. An object of this type can be discovered in
successive images of an area of sky because it noticeably shifts its
position while its surroundings remain fixed. Since either a distant
star moving quickly or a nearby star moving slower can exhibit the
same High Proper Motion, astronomers must use other measurements to
determine its distance from Earth.

During its star search, the team used the SkyMorph database for
NASA's Near Earth Asteroid Tracking program, to search for asteroids
that might be on a collision course for Earth. Pravdo is project
manager of the asteroid tracking program and is principal
investigator for SkyMorph, which was separately supported by NASA's
Applied Information Systems Research Program. Like High Proper Motion
stars, asteroids reveal themselves when they shift their position
against background stars in successive images. Automated telescopes
scan the sky, accumulating thousands of images for the Near Earth
Asteroid Tracking program, which have been incorporated into
SkyMorph, a web-accessible database, for use in other types of
astronomical research. 

Once the star revealed itself in the Near Earth Asteroid Tracking
images, the team found other images of the same patch of sky to
establish a rough distance estimate by a technique called
trigonometric parallax. This technique is used to calculate distances
to relatively close stars. As Earth progresses in its orbit around
the Sun, the position of a nearby star will appear to shift compared
to background stars much farther away -- the larger the shift, the
closer the star.

The team refined their initial distance estimate with another
technique called photometric parallax. They used the 3.5-meter (11.5
feet) Astrophysical Research Consortium telescope at the Apache Point
observatory, Sunspot, N.M., to observe the star and separate its
light into its component colors for analysis. This allowed the team
to determine what kind of star it is. The analysis indicates it's
similar to a red dwarf star (spectral type M6.5) that's shining by
fusing hydrogen atoms in its core, like our Sun (called a main
sequence star).

Once the type of star is known, its true brightness, called intrinsic
luminosity, can be determined. Since all light-emitting objects
appear dimmer as distance from them increases, the team compared how
bright the new star appeared in their images to its intrinsic
luminosity to improve their distance estimate.

Although the star resembles a M6.5 red dwarf, it actually appears
three times dimmer than expected for this kind of star at the initial
distance estimate of 7.8 light-years. The star could therefore really
be farther than the rough trigonometric distance indicates; or, if
the initial estimate holds, it could have unusual properties that
make it shine less brightly than typical M6.5 red dwarfs. A more
precise measurement of the new star's position to establish an
improved trigonometric parallax distance is underway at the U.S.
Naval Observatory. This will confirm or refute its status as one of
our closest neighbors by late this year. Either way, we might get
even more company soon: "Since the survey only covered a band of the
sky (about 25 degrees in declination), it is entirely possible that
other faint nearby objects remain to be discovered," said Teegarden.

In addition to Teegarden and Pravdo, the team includes Dr. Thomas
McGlynn of Goddard Space Flight Center; Dr. Michael Hicks and Dr.
Stuart Shaklan of JPL; Dr. Suzanne Hawley, Kevin Covey and Oliver
Fraser, of the University of Washington, Seattle; and Dr. Iann Reid
of the Space Telescope Science Institute, Baltimore, Md. An image and
more information are available at
http://www.gsfc.nasa.gov/topstory/2003/0520newstar.html  .

JPL manages the Near Earth Asteroid Tracking system and SkyMorph for
NASA's Office of Space Science, Washington, D.C.  JPL is managed by
the California Institute of Technology in Pasadena.

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