Institute for Astronomy
University of Hawaii
Dr. Eduardo Martin, 808-956-8637, firstname.lastname@example.org
Mrs. Karen Rehbock, 808-956-6829, email@example.com
For Immediate Release: May 20, 2002
ASTRONOMERS PONDER THE NATURE OF AN ULTRACOOL OBJECT IN ORION
A new substellar object, named SOri70, has been discovered near the
young star Sigma Orionis. Is it a young planet, or a wandering old
brown dwarf in the line of sight? This is a question to be discussed
by the astronomers attending the International Astronomical Union
Symposium on Brown Dwarfs that opens today on the Big Island of Hawaii.
Deep sky images and follow-up spectroscopy obtained by an international
team of astronomers revealed this extremely cool and dim object close
to the multiple stellar system Sigma Orionis. The astronomers made the
observations with large telescopes in Hawaii and the Canary Islands.
Since the acute visual observations of Sir William Herschel in the
eighteenth century, astronomers have noted a clustering of stars in a
region of the sky of about the size of the full moon surrounding the
hot star Sigma Orionis. Many X-ray emitting low-mass stars in this
cluster were found by Scott Wolk and Fred Walter of SUNY at Stony
Brook. Several brown dwarfs in this region were revealed by some of
the members of the team that today reports on the discovery of the
coolest and faintest object ever seen around Sigma Orionis.
The story of how SOri70 was found includes two of the world's most
powerful telescopes separated by more than 8,000 miles and about 4
years of international collaborative effort. It is an example of the
complicated work that is needed to hunt for the elusive brown dwarfs
and extrasolar planets.
In December 1998, team members Victor Bejar and Eduardo Martin
pointed one of the world's largest optical telescopes, the 10-meter
Keck I on Mauna Kea (Hawaii), at several fields around Sigma Orionis
and obtained CCD images of unprecedented sensitivity for this region
of the sky. They found several extremely faint red objects, but they
did not have enough information to determine their basic properties.
They had to wait patiently for a chance to obtain additional data.
It came when they used an infrared camera at the William Herschel
Telescope in La Palma (Canary Islands) in November 2000.
One of the objects turned out to have blue infrared colors despite
being very red at optical wavelengths, a unique signature of the
coolest known dwarfs. The unusual colors of these dwarfs are
explained by the presence of methane in their atmospheres, which
is a gas that can be present only at temperatures lower than about
1,200 degrees Kelvin (about 900 degrees Celsius or 1650 degrees
Fahrenheit). An object of this temperature must have a mass smaller
than a star.
The intriguing object was observed once more with the Keck I
telescope in December 2001 by team member Maria Rosa Zapatero Osorio
of the Laboratory for Fundamental Astrophysics in Madrid, Spain.
These observations confirmed spectroscopically the presence of
methane in the object, which unambiguously classifies it as a brown
dwarf or planet. If the object is located at the same distance as
the Sigma Orionis system (1,150 light-years from Earth), it should
have an age between 1 and 8 million years and a mass close to that
of Jupiter, the largest planet in the Solar System.
However, the distance to the object is not known yet; it will take
the sharp imaging capabilities of the Hubble Space Telescope to
determine it. There is about a 20% probability that SOri70 is a
wandering old brown dwarf that happens to be in the direction of
the Sigma Orionis, but is actually closer to Earth.
If the new ultracool dwarf is related to the Sigma Orionis system, it
would be the lowest mass extrasolar object imaged to date. Because it
would be located more than 180,000 astronomical units from Sigma
Orionis (more than 36,000 times the Jupiter-Sun distance), it would
challenge our ideas about the formation of extrasolar giant planets.
Four members of the science team are attending the International
Astronomical Union Symposium on Brown Dwarfs on the Big Island of
Hawaii during this week, namely, Dr. David Barrado y Navascues
(Laboratory for Fundamental Astrophysics in Madrid, Spain), Mr. Jose
Antonio Caballero (Instituto de Astrofisica de Canarias), Prof.
Eduardo Martin (University of Hawaii Institute for Astronomy) and Dr.
Maria Rosa Zapatero Osorio (Laboratory for Fundamental Astrophysics
in Madrid, Spain). Other team members include Dr. Victor Bejar
(Instituto de Astrofisica de Canarias), Dr. Joachim Eisloeffel
(Thueringer Landessternwarte Tautenburg, Germany), Dr. Reinhold
Mundt (Max Plank Institut fur Astronomie, Heidelberg, Germany), and
Dr. Rafael Rebolo (Instituto de Astrofisica de Canarias).
Members of the press and news media are invited to attend all
sessions of the Symposium at no cost. They are asked to check in at
the Conference Registration Desk at the Outrigger Waikoloa Beach
Hotel in order to obtain Symposium materials and other information
More information about the Brown Dwarfs Symposium is available at
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. Refer to
http://www.ifa.hawaii.edu for more information.
An image of the Sigma Orionis region. The multiple star Sigma Orionis,
which is visible with the naked eye, is at the center. A box indicates
the position of the planet candidate, which is only 8.7 arcminutes
from the star. The image was taken from the Digital Sky Survey and
has a size of 23 x 22 square arcminutes. The inset shows the infrared
image obtained at the William Herschel Telescope by Dr. Victor Bejar
and Prof. Eduardo Martin.
* High-resolution color for offset press (tif file; 6,897K)
* High-resolution grayscle for offset press (tif file; 1,727K)
* Small jpeg for Web (23K)
* Large jpeg for Web (58K)