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)