First Large Infrared Light Survey of Closest Young Star Pairs Yields New Multiple Stellar Systems (Forwarded)

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For Release: 9:20 AM, PST January 10, 2007

First Large Infrared Light Survey of Closest Young Star Pairs Yields New
Multiple Stellar Systems in Ophiuchus Star Forming Region

SEATTLE -- After three years of observations using the 10-meter Keck II
telescope in Hawaii, Lowell Observatory astronomer Lisa Prato announces
discovery of four new low-mass double star systems with separations similar
to the Earth-Sun distance or smaller. This survey also serendipitously
revealed five new wider binaries with separations of about 14 to 140 times
the Earth-Sun distance. The results provide significant new evidence to
better characterize the star and planet forming region in Ophiuchus.

"These very closely spaced young, low-mass star pairs are really exciting,"
said Prato, summarizing results of her study presented today at the American
Astronomical Society meeting in Seattle. "We can accurately measure the mass
ratios and ultimately the component masses of these pairs, along with their
abundance and other properties. These measurements give us new information
about star and planet formation in regions just now being probed at this
level of detail and resolution."

This research features the first such analysis for young, low-mass
spectroscopic (closely spaced) binary stars undertaken in infrared light.
The four new spectroscopic binary stars were previously unknown. One of
these new pairs is located in a complex and intriguing hierarchical
quadruple star system. The study comprised a sample of 33 young M stars --
the coolest, lowest mass class of stars -- in the Ophiuchus molecular cloud
and used the Keck II 10-meter telescope atop the 13,796-foot summit of Mauna
Kea in Hawaii. The stars in the survey program are approximately 450
light-years distant with an estimated mass range of between 0.3 to 0.7 solar
masses.

The study shows that because the size of a habitable zone around low-mass
stars corresponds to the typical distance between the stars in spectroscopic
binary pairs, the prevalence and properties of such binary star systems have
important consequences for potential terrestrial planet formation. "These
close, or 'spectroscopic binaries' have separations that are similar to the
Earth-Sun separation or even less," said Prato. "This raises the question
about what do these systems do to local planet formation? It might be
possible to have planets very far away orbiting both stars. On the other
hand, if the spectroscopic binary is spaced widely enough, could planets
possibly form close to one star? In any case, all this complexity throws a
wrench in the works, thus making it even more important to know how many of
these systems are out there in the nearby star and planet forming regions
like Ophiuchus."

For this survey, the large aperture Keck telescope was equipped on the many
nights necessary to observe such a large sample size with the facility's
infrared NIRSPEC spectrometer. Because M stars emit most of their light in
the infrared, using NIRSPEC on Keck allowed Prato to study these faint
targets with optimal facilities. Also, young stars still embedded within
this fascinating star and planet forming region are more readily detectable
in infrared light because dust blocks most visible light. "It is simply most
efficient to search in infrared light wavelengths for young M star
spectroscopic binaries with a large aperture telescope such as Keck," said
Prato. Together with colleague Michal Simon (Stony Brook University), Prato
pioneered the powerful application of infrared spectroscopy to the study of
close binary systems.

The paper, "A Survey for Young Spectroscopic Binary K7-M4 Stars in
Ophiuchus," has been accepted for publication by the Astrophysical Journal
(http://arxiv.org/pdf/astro-ph/0611636). Lisa Prato is the sole author. The
research goal was to find young M star spectroscopic binaries in the target
region by searching for variability in radial velocity and to measure the
mass ratios of any new systems discovered. Mass ratios of the spectroscopic
binary stars are determined by the Doppler shift, that is by measuring the
spectral signatures, indicating radial velocities, of both components in the
spectroscopic binary pairs. Prato discovered two double-lined spectroscopic
binary systems, two single-lined systems, and one radial velocity variable.

The occurrence of the young, low-mass, spectroscopic binary star pairs
discovered in the study is about 12 percent; this compares closely with
other research programs that have measured the abundance of nearby older
star spectroscopic binaries, as well as studies to measure the number of
higher mass young spectroscopic binary stars in various star forming
regions.

"My research so far leads me to suspect that there are more young, low-mass
spectroscopic binary stars in Ophiuchus and other star forming regions
awaiting discovery," Prato said. "These young, exceptionally small
separation binary stars orbiting each other in such close proximity,
possibly interacting with dust and gas distributed throughout the systems,
will help to determine the potential for planet formation in habitable
zones. Young spectroscopic binaries also provide a unique opportunity to
measure very accurate stellar mass ratios and eventually stellar masses --
information that helps astronomers to broadly understand star formation and
evolution."

Prato plans to further explore this rich and diverse sample of stars to
study circumstellar dust, rotational velocities, and the wide binary
properties in future research. Hubble Space Telescope or adaptive optics
observations may detect even more wide binaries. Also, a more dense sampling
is needed to determine the orbital properties of the newly discovered
spectroscopic binaries.

This research was supported by NSF and awards from NASA's Keck PI Data
Analysis Fund. Data for this project were obtained at the W.M. Keck
Observatory from telescope time allocated to NASA through the agency's
scientific partnership with the California Institute of Technology and the
University of California.

About Lowell Observatory

Lowell Observatory is a private, non-profit research institution founded in
1894 by Percival Lowell. The Observatory has been the site of many important
findings including the discovery of the large recessional velocities of
galaxies by Vesto Slipher in 1912-1914 (a result that led ultimately to the
realization the universe is expanding), and the discovery of Pluto by Clyde
Tombaugh in 1930. Today, Lowell's 19 astronomers use ground-based telescopes
around the world, telescopes in space, and NASA planetary spacecraft to
conduct research in diverse areas of astronomy and planetary science. Lowell
Observatory currently has four research telescopes at its Anderson Mesa dark
sky site east of Flagstaff, Arizona, and is building a 4-meter class
research telescope, the Discovery Channel Telescope, in partnership with
Discovery Communications, Inc.

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