Institute for Astronomy<br />University of Hawaii<br />Honolulu, Hawaii<br /><br />Contacts:<br />Dr. Eduardo Martin, 808-956-8637, ege@ifa.hawaii.edu<br />Mrs. Karen Rehbock, 808-956-6829, rehbock@ifa.hawaii.edu<br /><br />For Immediate Release: May 20, 2002<br /><br />ASTRONOMERS PONDER THE NATURE OF AN ULTRACOOL OBJECT IN ORION<br /><br />A new substellar object, named SOri70, has been discovered near the<br />young star Sigma Orionis. Is it a young planet, or a wandering old<br />brown dwarf in the line of sight? This is a question to be discussed<br />by the astronomers attending the International Astronomical Union<br />Symposium on Brown Dwarfs that opens today on the Big Island of Hawaii.<br /><br />Deep sky images and follow-up spectroscopy obtained by an international<br />team of astronomers revealed this extremely cool and dim object close<br />to the multiple stellar system Sigma Orionis. The astronomers made the<br />observations with large telescopes in Hawaii and the Canary Islands.<br /><br />Since the acute visual observations of Sir William Herschel in the<br />eighteenth century, astronomers have noted a clustering of stars in a<br />region of the sky of about the size of the full moon surrounding the<br />hot star Sigma Orionis. Many X-ray emitting low-mass stars in this<br />cluster were found by Scott Wolk and Fred Walter of SUNY at Stony<br />Brook. Several brown dwarfs in this region were revealed by some of<br />the members of the team that today reports on the discovery of the<br />coolest and faintest object ever seen around Sigma Orionis.<br /><br />The story of how SOri70 was found includes two of the world's most<br />powerful telescopes separated by more than 8,000 miles and about 4<br />years of international collaborative effort. It is an example of the<br />complicated work that is needed to hunt for the elusive brown dwarfs<br />and extrasolar planets.<br /><br />In December 1998, team members Victor Bejar and Eduardo Martin<br />pointed one of the world's largest optical telescopes, the 10-meter<br />Keck I on Mauna Kea (Hawaii), at several fields around Sigma Orionis<br />and obtained CCD images of unprecedented sensitivity for this region<br />of the sky. They found several extremely faint red objects, but they<br />did not have enough information to determine their basic properties.<br />They had to wait patiently for a chance to obtain additional data.<br />It came when they used an infrared camera at the William Herschel<br />Telescope in La Palma (Canary Islands) in November 2000.<br /><br />One of the objects turned out to have blue infrared colors despite<br />being very red at optical wavelengths, a unique signature of the<br />coolest known dwarfs. The unusual colors of these dwarfs are<br />explained by the presence of methane in their atmospheres, which<br />is a gas that can be present only at temperatures lower than about<br />1,200 degrees Kelvin (about 900 degrees Celsius or 1650 degrees<br />Fahrenheit). An object of this temperature must have a mass smaller<br />than a star.<br /><br />The intriguing object was observed once more with the Keck I<br />telescope in December 2001 by team member Maria Rosa Zapatero Osorio<br />of the Laboratory for Fundamental Astrophysics in Madrid, Spain.<br />These observations confirmed spectroscopically the presence of<br />methane in the object, which unambiguously classifies it as a brown<br />dwarf or planet. If the object is located at the same distance as<br />the Sigma Orionis system (1,150 light-years from Earth), it should<br />have an age between 1 and 8 million years and a mass close to that<br />of Jupiter, the largest planet in the Solar System.<br /><br />However, the distance to the object is not known yet; it will take<br />the sharp imaging capabilities of the Hubble Space Telescope to<br />determine it. There is about a 20% probability that SOri70 is a<br />wandering old brown dwarf that happens to be in the direction of<br />the Sigma Orionis, but is actually closer to Earth.<br /><br />If the new ultracool dwarf is related to the Sigma Orionis system, it<br />would be the lowest mass extrasolar object imaged to date. Because it<br />would be located more than 180,000 astronomical units from Sigma<br />Orionis (more than 36,000 times the Jupiter-Sun distance), it would<br />challenge our ideas about the formation of extrasolar giant planets.<br /><br />Four members of the science team are attending the International<br />Astronomical Union Symposium on Brown Dwarfs on the Big Island of<br />Hawaii during this week, namely, Dr. David Barrado y Navascues<br />(Laboratory for Fundamental Astrophysics in Madrid, Spain), Mr. Jose<br />Antonio Caballero (Instituto de Astrofisica de Canarias), Prof.<br />Eduardo Martin (University of Hawaii Institute for Astronomy) and Dr.<br />Maria Rosa Zapatero Osorio (Laboratory for Fundamental Astrophysics<br />in Madrid, Spain). Other team members include Dr. Victor Bejar<br />(Instituto de Astrofisica de Canarias), Dr. Joachim Eisloeffel<br />(Thueringer Landessternwarte Tautenburg, Germany), Dr. Reinhold<br />Mundt (Max Plank Institut fur Astronomie, Heidelberg, Germany), and<br />Dr. Rafael Rebolo (Instituto de Astrofisica de Canarias).<br /><br />Members of the press and news media are invited to attend all<br />sessions of the Symposium at no cost. They are asked to check in at<br />the Conference Registration Desk at the Outrigger Waikoloa Beach<br />Hotel in order to obtain Symposium materials and other information<br />of interest.<br /><br />More information about the Brown Dwarfs Symposium is available at<br />
http://anansi.ifa.hawaii.edu/iau211/<br /><br />The Institute for Astronomy at the University of Hawaii conducts<br />research into galaxies, cosmology, stars, planets, and the Sun. Its<br />faculty and staff are also involved in astronomy education, deep<br />space missions, and in the development and management of the<br />observatories on Haleakala and Mauna Kea. Refer to<br />
http://www.ifa.hawaii.edu for more information.<br /><br />Images:<br /><br />An image of the Sigma Orionis region. The multiple star Sigma Orionis,<br />which is visible with the naked eye, is at the center. A box indicates<br />the position of the planet candidate, which is only 8.7 arcminutes<br />from the star. The image was taken from the Digital Sky Survey and<br />has a size of 23 x 22 square arcminutes. The inset shows the infrared<br />image obtained at the William Herschel Telescope by Dr. Victor Bejar<br />and Prof. Eduardo Martin. <br /><br />* High-resolution color for offset press (tif file; 6,897K)<br />
http://www.ifa.hawaii.edu/info/press-releases/brwnDwarf_300cmyk.tif<br />* High-resolution grayscle for offset press (tif file; 1,727K)<br />
http://www.ifa.hawaii.edu/info/press-releases/brwnDwarf_300gray.tif<br />* Small jpeg for Web (23K)<br />
http://www.ifa.hawaii.edu/info/press-releases/brwnDwarf_250web.jpg<br />* Large jpeg for Web (58K)<br />
http://www.ifa.hawaii.edu/info/press-releases/brwnDwarf_480web.jpg
