VLBA Helps Build New Picture of Star-Forming Regions (Forwarded)

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EMBARGOED For Release: 2:00 p.m., PST, Monday, January 8, 2007

VLBA Helps Build New Picture of Star-Forming Regions

New, high-precision distance measurements by the National Science
Foundation's Very Long Baseline Array (VLBA) radio telescope are providing
a major advance for astronomers trying to understand how stars form. "A
large improvement in measuring the distance to a young, still-forming star
means a large improvement in measuring characteristics such as its mass
and intrinsic brightness," said Laurent Loinard, of the National
University of Mexico (UNAM). Loinard, Amy Mioduszewski of the National
Radio Astronomy Observatory, UNAM graduate student Rosa Torres and UNAM
professor Luis Rodriguez presented their findings to the American
Astronomical Society's meeting in Seattle, Washington.

"Most of what we know about the processes of star formation has come from
studying young stars in a few, relatively nearby regions," Loinard said.
"However, estimates of the distance to these regions have been imprecise.
That imprecision has limited the ability of real-world observations to
improve theoretical models for star formation," he added.

The new VLBA distance measurements are great improvements over earlier
estimates. For example, earlier work placed a famous young stellar system
in the constellation Taurus between 423 and 489 light-years from Earth.
The new VLBA measurements narrow the range to 418-422 light-years. "Our
observations brought the error in this measurement down from 66
light-years to four," Mioduszewski said.

The new VLBA observations also refined the distance estimate to another
star-forming region in the constellation Ophiuchus.

The new results are part of a long-term project led by Loinard and
Mioduszewski to make precise distance measurements to individual young
stars within well-studied regions of prolific star formation. They do this
by measuring the tiny apparent shift of the star's position against the
background sky caused by Earth's rotation around the Sun. This method,
called trigonometric parallax, produces a direct, unambiguous measurement
of the star's distance.

"The VLBA is the only instrument in the world that can do this on these
objects," Loinard explained. This is because the visible light from young
stars is dimmed by the cloud of gas and dust from which they are being
formed. In addition, young stars also are often surrounded by material
that obscures their visible light. This means that even the Hipparcos
satellite, which measured distances of more than 100,000 stars, was
handicapped when it came to young stars. However, processes occurring in
the magnetic fields of newly-formed stars often produce bright radio
emission that the VLBA can detect readily.

The VLBA, a system of 10 radio-telescope antennas stretching from Hawaii
to the Caribbean, provides the best ability to see fine detail, called
resolving power, of any astronomical tool in the world. The VLBA can
routinely produce images hundreds of times more detailed than those
produced by the Hubble Space Telescope. The VLBA's tremendous resolving
power is what permits the astronomers to make the precise distance
determinations.

The scientific payoff is great. The improved distance measurements allow
better determinations of the young stars' physical characteristics. By
measuring distances to multiple stars in a star-forming region, the
astronomers can build a three-dimensional picture of the region. Observing
the stars over a period of years will allow the scientists to determine
their speeds and motions.

"All this new information about the stars and the environment in which
they are formed will greatly improve our ability to understand such
regions and the processes that turn clouds of gas and dust into stars,"
said Mioduszewski.

The results the astronomers announced in Seattle are just the beginning of
their project, they said. They intend to use the VLBA to study additional
star-forming regions in addition to more stars within the regions already
studied.

"By carefully building up well-measured, three-dimensional pictures of
several star-forming regions, as well as learning about the motions of
stars within those regions, we expect that we'll find some surprises that
revise our understanding of the all-important process of star formation,"
Loinard said.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

IMAGE CAPTION:
[http://www.nrao.edu/pr/2007/starfmpa...lustration.jpg
(153KB)]
Trigonometric Parallax method determines distance to star by measuring its
slight shift in apparent position as seen from opposite ends of Earth's
orbit. CREDIT: Bill Saxton, NRAO/AUI/NSF

OTHER IMAGES & ANIMATION:

* Animation of apparant motion on sky of young star T Tauri S (MPEG, 891KB)
http://www.nrao.edu/pr/2007/starfmpa.../parallax.mpeg
* Still Frame from above animation (14KB)
http://www.nrao.edu/pr/2007/starfmpa...moviestill.jpg
* B&W Plot of T Tauri S Parallax motion (51KB)
http://www.nrao.edu/pr/2007/starfmpa...allax.plot.jpg