From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue May 20 2003 - 18:09:44 PDT
----- Original Message -----
From: Mark Hess
Sent: Tuesday, May 20, 2003 2:58 PM
To: News Media list.serv
Subject: NEWLY-DISCOVERED STAR MAY BE THIRD-CLOSEST
William Steigerwald
May 20, 2003
NASA Goddard Space Flight Center
(Phone: 301/286-5017
Jane Platt
NASA Jet Propulsion Laboratory
(Phone: 818/354-0880
Release: 03-57
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 (JPL).
If its distance estimate 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 (HPM) objects. A HPM object 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
HPM, astronomers must use other measurements to determine its
distance from Earth.
During its star search, the team used the SkyMorph database for the
Near Earth Asteroid Tracking (NEAT) program. NEAT is a NASA program,
run by the Jet Propulsion Laboratory (JPL), Pasadena, Calif., to
search for asteroids that might be on a collision course for Earth.
SkyMorph was separately supported by NASA's Applied Information
Systems Research Program. Like HPM 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 NEAT 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 NEAT 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 the
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
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 NEAT survey only covered a band of
the sky (+/- 25 degrees in declination), it is entirely possible that
other faint nearby objects remain to be discovered," said Teegarden.
The team includes B. J. Teegarden, T. McGlynn (NASA/Goddard); S. H.
Pravdo, M. Hicks, S. B. Shaklan (NASA/JPL); K. Covey, O. Fraser, S.
H. Hawley (U. of Wash.); and I. N. Reid (Space Telescope Science
Institute).
For an image and more information, refer to:
http://www.gsfc.nasa.gov/topstory/2003/0520newstar.html
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