A Rare Quartet of Stars May Unlock Secrets of Stellar Evolution (Forwarded)

Institute for Astronomy
University of Hawaii at Manoa
Manoa, Hawaii

Contacts:

Dr. Evgenya Shkolnik
NASA Astrobiology Institute / Institute for Astronomy
University of Hawaii at Manoa
www.ifa.hawaii.edu/~shkolnik/

Dr. Michael C. Liu
Institute for Astronomy
University of Hawaii at Manoa
1-808-956-6666

Mrs. Karen Rehbock
Assistant to the Director
Institute for Astronomy
University of Hawaii at Manoa
1-808-956-6829

Dr. I. Neill Reid
Space Telescope Science Institute
1-410-338-4971

Embargoed until Thursday, January 10, 2008 10:30 a.m. CST (6:30 a.m. HST)

A Rare Quartet of Stars May Unlock Secrets of Stellar Evolution

Astronomers using telescopes on Mauna Kea have found an extremely rare
quartet of stars that orbit each other within a region smaller than
Jupiter's orbit round the Sun. The quartet appears as a speck of light even
when viewed with the world's most powerful telescopes but its spectrum
reveals not one, but four distinct stars arranged in two pairs. Astronomers
are now struggling to work out whether they could have been born that way,
or were forced together by a dense disk of gas in their youth.

This discovery that the star called "BD -22 5866" is really a very rare
system of four closely orbiting stars was announced by Dr. Evgenya Shkolnik
of the University of Hawaii's Institute for Astronomy and the NASA
Astrobiology Institute on January 8, 2008, at the annual meeting of the
American Astronomical Society in Austin, TX. She and collaborators Dr.
Michael C. Liu, also of the University of Hawaii, and Dr. I. Neill Reid of
the Space Telescope Science Institute in Baltimore were monitoring several
hundred nearby low-mass stars when one observation caught their attention
because it was unlike anything they had seen before.

At the time of the observations, two of the stars were orbiting each other
at 133 km/s (300,000 mph, a speed that would get you from Honolulu to New
York in less than a minute), while the second pair moved at a more modest
speed of 52 km/s (120,000 mph). Using these speeds and the stars' masses,
astronomers were able to determine the maximum sizes of their oddly tight
orbits. Less than 1 in 2,000 stars observed might be such tightly bound
systems, making this quadruple stellar system extremely rare.

The first pair orbits each other in less than 5 days with the orbits radius
of at most 0.06 AU (where 1 AU is the distance from Earth to the sun). The
second pair orbits with a period of less than 55 days and a maximum radius
of 0.26 AU. The two pairs are orbiting each other with a maximum radius of
only 5.8 AU (= orbital period of less than 9 years), about the same as
Jupiter's distance from the sun.

"The extraordinarily tight configuration of this stellar system tells us
that there may have been a single gaseous disk that forced them into such
small orbits within the first 100,000 years of their evolution, as the stars
could not have formed so close to one another. This is the first evidence of
a disk completely encompassing four stars," says Dr. Shkolnik. "It is
remarkable how much a single stellar spectrum can tell us about both the
present and the past of these stars."

The data were acquired at the Keck I 10-m (33-foot) telescope and on the
Canada-France-Hawaii 3.6-m (12-foot) telescope, both located on the summit
of Mauna Kea, a 14,000-foot-high dormant volcano on the Big Island of
Hawaii. Each telescope is equipped with a high-resolution spectrograph, an
instrument capable of breaking up the star's light into different colors (or
wavelengths), known as a spectrum.

The stellar system is 51 pc (or 166 light-years) away from the Sun and lies
just south of the constellation Aquarius (The Water Bearer). Though BD -22
5866 cannot be seen without a telescope, it is relatively bright and will be
carefully monitored to map the orbits in more detail. Since most stars form
as part of a binary- or multiple-star system, the enormous potential of this
quadruple system to give us previously unavailable physical information
makes it a key to unlocking a few mysteries of stellar evolution.

This work has been submitted to the Astrophysical Journal Letters and was
funded by the NASA Astrobiology Institute and the University of Hawaii.

Founded in 1967, the Institute for Astronomy at the University of Hawaii at
Manoa 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.

IMAGE CAPTIONS:

[Figure 1:
http://www.ifa.hawaii.edu/info/press...eQuand_rgb.jpg
(808KB)]
Artist's view of the gaseous disk that may have once engulfed and maneuvered
the quadruple stellar system into its unusually small orbit. (Credit:
Institute for Astronomy, University of Hawaii)

[Figure 2:
http://www.ifa.hawaii.edu/info/press...olarsystem.tif
(100KB)]
A to-scale schematic of the quadruple stellar system overlayed for
comparison with a diagram of the solar system's planetary orbits. (Credit:
Evgenya Shkolnik)