Astronomers Use "Laser-Vision" To Find (Strange) New Brown DwarfTwins (Forwarded)

Institute for Astronomy
University of Hawaii
Honolulu, Hawaii

Contacts:
Dr. Michael C. Liu
Institute for Astronomy
University of Hawaii at Manoa
Honolulu, Hawaii 96822
1-808-956-6666

Dr. Sandy Leggett
United Kingdom Infrared Telescope (UKIRT)
Joint Astronomy Centre
Hilo, HI
1-808-969-6523

Dr. David Golimowski
Department of Physics & Astronomy
Johns Hopkins University
1-808-876-7600 x107

For immediate release: January 10, 2006

Astronomers Use "Laser-Vision" To Find (Strange) New Brown Dwarf Twins

Astronomers are reporting today discoveries of several ultracool brown
dwarf binary systems found using the new Keck laser guide star adaptive
optics system, including a strange kind of binary never seen before. The
results are being announced by a team of U.S. astronomers led by Dr.
Michael C. Liu of the Institute for Astronomy at the University of
Hawaii. The team is presenting its findings at the 207th American
Astronomical Society meeting in Washington, D.C.

The results shed light on the puzzling formation mechanism and
atmospheres of brown dwarfs, and would not have been possible without
the ultra-sharp images produced by the laser guide star system on the
Keck Telescope. Among the discoveries, the team has determined that a
brown dwarf previously considered a single object is actually a closely
spaced pair of brown dwarfs with very unusual properties.

"Keck's new 'laser vision' is a big step forward in our quest to
understand the origins and atmospheres of these intriguing objects,
which are partly like stars and partly like planets," said Dr. Liu.

Discovered only a decade ago, brown dwarfs represent a class of
low-mass, ultracool objects -- occupying the once theoretical gap
between ordinary stars and giant planets. Hundreds of brown dwarfs are
now known, but their origins and physical properties remain mysteries
that have yet to be fully understood by astronomers. Part of the
challenge lies in the fact that nearby brown dwarfs have a widely varied
and unknown mix of ages, masses, and compositions.

To circumvent this problem, Dr. Liu and his collaborators have been
conducting a survey for nearby brown dwarf binaries, namely pairs of
brown dwarfs that are orbiting each other. Since binaries are born at
the same time and made out of the same composition, comparing the two
components removes much ambiguity in the interpretation.

"Biologists study human twins to understand whether differences among
people can arise even if they have the same age and genetic makeup. In a
similar fashion, we are finding and studying brown dwarf twins in order
to understand what causes differences among these objects, and thereby
learn about their physical properties," said Dr. Liu.

In the course of their survey, the team found a very unusual type of
brown dwarf binary, whose two components have very different
atmospheres. The object is called SDSS J1534+1615 and was first
identified as a brown dwarf candidate in 2004 by the Sloan Digital Sky
Survey (SDSS) and confirmed through follow-up ground-based infrared
observations at the United Kingdom Infrared Telescope (UKIRT) and the
NASA Infrared Telescope Facility (IRTF), both on Mauna Kea.

Initially thought to be a single object, Dr. Liu's team found that SDSS
J1534+1615 is in fact a very closely spaced binary, with an angular
separation of only 0.11 arcseconds or about 1/20,000 of the diameter of
the full moon. The physical separation is about four Astronomical Units,
or four times the distance between the Earth and the Sun. SDSS
J1534+1615 is about 110 light years away from Earth, located in the
constellation of Serpens (the Serpent).

What is quite surprising about SDSS J1534+1615, and makes it unique
compared to the ~40 previously known brown dwarf binaries, is that the
two "twin" components have very different appearances, despite their
identical ages and compositions. All previously known brown dwarf
binaries have similar atmospheric colors, and one component is always
brighter than the other regardless of which color filter is used for
imaging. But in the case of SDSS J1534+1615, the two components have
very different atmospheric colors in infrared light --- one is much
redder than the other. And even more unusual, the brighter component
depends on the observing filter.

"We've never seen a pair of brown dwarfs like this. They will tell us
quite a bit about what is happening in the atmospheres of these
planet-like objects," said Dr. Sandy K. Leggett of the United Kingdom
Infrared Telescope and co-author on the study.

The very different atmospheres of the two components probably arise from
differences in their cloud content. Just like planets in our own solar
system, many brown dwarfs are thought to possess clouds in their
atmospheres. However, brown dwarf clouds are composed of iron particles,
unlike the water clouds on the Earth. These iron clouds cause the very
red appearance of one component of SDSS J1534+1615. The other component
likely has fewer and/or more fragmented clouds, leading to a very
different appearance.

"The very different atmospheres of these otherwise very similar brown
dwarfs are quite unusual. It's as if your house was completely clouded
over, but your next-door neighbor sees sunny skies overhead," remarked
co-author Dr. David A. Golimowski of Johns Hopkins University.

The discoveries are the result of an ongoing survey of nearby brown
dwarfs being carried out by Dr. Liu and his collaborators at the
10-meter (400-inch) Keck II Telescope on Mauna Kea, Hawaii. Keck II is
the first large (8-10 meter) telescope equipped with a laser guide star
adaptive optics (AO) system.

Adaptive optics corrects astronomical images for the blurring caused by
the Earth's turbulent atmosphere. While astronomers have been using this
technology for nearly two decades, brown dwarfs have always been far too
faint for traditional AO systems, which only work with bright stars. The
Keck laser system creates an "artificial star" in the sky, which can
then be pointed at the brown dwarfs to produce unprecedentedly sharp
infrared images.

The resulting images are the sharpest ever obtained of any brown dwarf
binary in infrared light, with angular resolution as good as 1/20 of an
arcsecond, about 1/400,000 the diameter of the full moon. If a person's
vision were as sharp as the Keck adaptive optics system, he would be
able to read a magazine that was about two and a half miles away.

"This new capability provides us with infrared images three to four
times sharper than those produced by the Hubble Space Telescope. This is
essential to separate these very closely spaced brown dwarf binaries and
to study their atmospheres. Without it, these objects would falsely
appear to be a single object," Dr. Liu added.

Brown dwarfs are very faint, ultra-cool objects with masses less than
seven percent of the Sun's mass (or about 70 times the mass of Jupiter).
They are commonly referred to as "failed stars," since they lack
sufficient mass to generate their own energy via nuclear fusion like
stars do. As a result, they have very low surface temperatures, less
than one-fourth of the Sun's surface temperature, and are very dim. In
many respects, brown dwarfs are much closer to the gas giant planets in
our solar system, given that both planets and brown dwarfs have much
lower masses and temperatures than stars."

In fact, we suspect that some other nearby brown dwarfs that are thought
to be single objects may in fact be thus-far undetected binaries. And
some of them may belong to this strange new class of binaries
established by SDSS J1534+1615. We're eager to look at more nearby brown
dwarfs with Keck's ultra-sharp vision in the coming months," Dr. Liu
exclaimed.

Co-authors on the results presented today are Sandy Leggett of the
United Kingdom Infrared Telescope; David Golimowski and Kuenley Chiu of
Johns Hopkins University; Xiaohui Fan of the University of Arizona; Tom
Geballe of Gemini Observatory; Donald Schneider of the Pennsylvania
State University; and Jon Brinkmann of Apache Point Observatory.

The results are described in an upcoming paper in The Astrophysical
Journal. This research has been supported by the National Science
Foundation and the Alfred P. Sloan Foundation.

The Institute for Astronomy at the University of Hawaii conducts
research into galaxies, cosmology, stars, planets, and the sun. Its
faculty and staff are also involved in astronomy education, deep space
missions, and in the development and management of the observatories on
Haleakala and Mauna Kea.

Established in 1907 and fully accredited by the Western Association of
Schools and Colleges, the University of Hawaii is the state's sole
public system of higher education. The UH System provides an array of
undergraduate, graduate, and professional degrees and community programs
on 10 campuses and through educational, training, and research centers
across the state. UH enrolls more than 50,000 students from Hawaii, the
U.S. mainland, and around the world.

Funding for the SDSS has been provided by the Alfred P. Sloan
Foundation, the Participating Institutions, the National Science
Foundation, the U.S. Department of Energy, the National Aeronautics and
Space Administration, the Japanese Monbukagakusho, the Max Planck
Society, and the Higher Education Funding Council for England. The SDSS
Web Site is http://www.sdss.org/ . The SDSS is managed by the
Astrophysical Research Consortium for the Participating Institutions.
The Participating Institutions are the American Museum of Natural
History, Astrophysical Institute Potsdam, University of Basel, Cambridge
University, Case Western Reserve University, University of Chicago,
Drexel University, Fermilab, the Institute for Advanced Study, the Japan
Participation Group, Johns Hopkins University, the Joint Institute for
Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and
Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences
(LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for
Astronomy (MPA), the Max-Planck-Institute for Astrophysics (MPIA), New
Mexico State University, Ohio State University, University of
Pittsburgh, University of Portsmouth, Princeton University, the United
States Naval Observatory, and the University of Washington.

UKIRT is operated by the Joint Astronomy Centre on behalf of the U.K.
Particle Physics and Astronomy Research Council.

The IRTF is operated by the University of Hawaii under Cooperative
Agreement no. NCC 5-538 with the National Aeronautics and Space
Administration, Office of Space Science, Planetary Astronomy Program.

IMAGE CAPTIONS:

[Image 1:
http://www.ifa.hawaii.edu/info/press...Liu-image1.jpg (202KB)]
Color finding chart of SDSS J1534+1615 based on optical images obtained
at 0.5, 0.8, and 0.9 microns. The images are 80 arcseconds on a side.
(Credit: Xiaohui Fan and the Sloan Digital Sky Survey Collaboration)

[Image 2:
http://www.ifa.hawaii.edu/info/press...image2-big.jpg
(15KB)]
High-resolution image of SDSS J1534+1615 obtained with the Keck laser
guide star adaptive optics system in infrared light at wavelengths of
1.2, 1.6, and 2.2 microns. The image is 0.75 arcseconds on a side, and
the binary is separated by 0.11 arcseconds. (Credit: Michael Liu,
University of Hawaii)