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**Contact data are at the end.**

November 14, 2006

NOAO 06-14

TWENTY NEW STARS IN THE NEIGHBORHOOD

Astronomers have identified 20 new stellar
systems in our local solar neighborhood,
including the twenty-third and twenty-fourth
closest stars to the Sun. When added to
eight other systems announced by this team
and six by other groups since 2000,
the known population of the Milky Way galaxy
within 33 light-years (10 parsecs)
of Earth has grown by 16 percent in just the
past six years.

The discoveries were made by a group called the
Research Consortium on Nearby Stars
(RECONS), which has been using small telescopes
at the National Science Foundation’s
Cerro Tololo Inter-American Observatory (CTIO) in
the Chilean Andes since 1999.
These new results will appear in the December
2006 issue of the Astronomical Journal.

“Our goal is to help complete the census of our
local neighborhood and provide some
statistical insights about the demographics of
stars in our galaxy – their masses,
their evolutionary states, and the frequency of
multiple star systems,” says RECONS
Project Director Todd Henry of Georgia State
University in Atlanta. “Due to their
proximity, these systems are also excellent
targets for exoplanet searches, and
ultimately, for astrobiological studies of
whether any planets that are found could
support life.”

The 20 newly reported objects are all red dwarf
stars, which now comprise 239 of
the 348 known objects beyond our Solar System
within the 10-parsec boundary of
the RECONS survey. Thus, red dwarfs likely
account for at least 69 percent of the
Milky Way’s residents.

“Red dwarfs are among the faintest but most
populous objects in the Milky Way,”
Henry explains. “Although you can’t see a single
one with the naked eye, there are
swarms of them throughout the galaxy.”

The distances to these stars were measured via a
classic trigonometric parallax
technique using the 0.9-meter telescope at
CTIO. The parallax technique for measuring
the distance to a star takes advantage of the
simple geometry of Earth's changing
position in the cosmos as it orbits the Sun each
year. The apparent back and forth
motion of a nearby star during the year reflects
the motion of the Earth around the Sun,
much like how your finger appears to jump back
and forth in front of your eyes if you
blink one eye, then the other.

From Earth, nearby stars appear to make tiny
ellipses in the sky because the Earth
does not jump from one side of its orbit to
another, but slides smoothly around the Sun.
The extreme points of the Earth in its orbit are
much like the positions of your eyes in
your head, and the size of the apparent motion of
your finger depends on how close
you hold it to your eyes – when nearer, it seems
to jump more, relative to distant
background objects.

With observations over several years, it is
possible to make parallax measurements
with an accuracy of 1 milliarcsecond (0.0000003
degrees), or about one two-millionth
the width of the full Moon. This allows
astronomers to measure distances accurate
to better than 10 percent out to more than
300 light-years.

The team of astronomers includes Henry, Wei-Chun
Jao, John Subasavage and
Thom Beaulieu of Georgia State University, Phil
Ianna of the University of Virginia
in Charlottesville, and Edgardo Costa and Rene
Mendez of the Universidad de Chile.
The RECONS long-term parallax program began
under the auspices of the
National Optical Astronomy Observatory (NOAO)
Survey Program in 1999, and
continues via the Small and Moderate Aperture
Research Telescope System (SMARTS) Consortium.

“We expect to announce more systems within 10
parsecs in the future,” notes Henry.
“The pool of nearby stars without accurate
parallaxes is nowhere near drained.”

The purpose of this survey is to discover and
characterize overlooked stars and
brown dwarfs in the vicinity the Sun. Objects
are scrutinized by measuring their
positions (and wobbles), their brightnesses and
colors, and by taking spectroscopic
fingerprints to examine their atmospheric
composition. The estimated "missing"
population of solar neighborhood members is
expected to be composed primarily
of very low mass stars with spectral type M
(known as red dwarfs), and objects
of spectral types L and T, many of which are
actually brown dwarfs with too little
mass to start long-term thermonuclear reactions.

These L- and T-dwarfs shine feebly, glowing
only because of energy leaking out
since their gravitational formation, many
billions of years ago. RECONS has also
found several nearby white dwarfs, which are the
burned-out cores of intermediate-
mass stars, lurking in the solar neighborhood.

For more information, see the RECONS Web page at:

http://www.chara.gsu.edu/RECONS/

The Chilean members of the team have been supported
by the Fondo Nacional de Investigacion Cientifica y
Tecnologica and the Chilean Centro de Astrofisica.
The team from the United States has been
supported by NASA's Space Interferometry
Mission, the National Science Foundation, and
Georgia State University.

Cerro Tololo Inter-American Observatory, based in
La Serena, Chile, is part of the
National Optical Astronomy Observatory, which is
operated by the Association of
Universities for Research in Astronomy Inc.
(AURA), under a cooperative agreement
with the NSF.

-end-

CONTACTS:
Douglas Isbell
National Optical Astronomy Observatory
Phone: (520) 318-8214
E-mail: disbell@noao.edu

Todd Henry
Department of Physics & Astronomy
Georgia State University
Atlanta, GA
phone: 404-463-9954
email: thenry@chara.gsu.edu

Phil Ianna
Department of Astronomy
University of Virginia
phone: 434-296-4457
email: p.ianna@juno.com

Edgardo Costa
Departamento de Astronomia
Universidad de Chile
Santiago, Chile
phone: 56-2-2294101
email: costa@das.uchile.cl

Rene Mendez
Departamento de Astronomia
Universidad de Chile
Santiago, Chile
phone: 56-2-2294101
email: rmendez@das.uchile.cl