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Issued by: Issued by: Images, notes, and contact details appear below. 30 May 2007 Discovery Narrows the Gap Between Planets and Brown DwarfsThe coolest-known star-like object beyond the solar system is giving astronomers a new look at the differences between massive planets and the smallest brown dwarfs. This newly discovered object, called ULAS J0034-00 and located in the constellation of Cetus, has a record-setting surface temperature of 600-700 K, cooler than any known solitary brown dwarf. In addition, it's a relative lightweight, with an estimated mass of only 15-30 times that of Jupiter (although they both have about the same diameter). The finding was announced today at the 210th American Astronomical Society meeting in Honolulu, Hawai'i, by an international team of astronomers that used the United Kingdom Infrared Telescope (UKIRT) and made followup observations with Gemini Observatory's Near Infrared Spectrograph (GNIRS) on Gemini South. Their discovery suggests that even lower-mass objects could be found. If so, they would continue to test the boundary between high-mass planets and the smallest brown dwarfs. J0034 was discovered in the very early stages of the UKIRT Infrared Deep Sky Survey (UKIDSS) -- the world's deepest-ever near-infrared sky survey -- using an instrument called the Wide Field Camera (WFCAM). The brown dwarf is particularly remarkable since it has a lower temperature than any such object previously discovered. According to team leader Steve Warren of Imperial College London, "Only planets are cooler, and they are by definition bound to a parent star." The discovery was initiated by post-doctoral researcher Daniel Mortlock, who first noticed the unusual object in the UKIRT survey images. "Identifying an object like J0034-00 is a more challenging version of finding a needle in a haystack," said Mortlock. "In this case it was like looking for a piece of slightly reddish straw rather than a nice shiny needle." Follow-up spectroscopic observations, critical for determining the brown dwarf's temperature and likely mass were obtained with the Gemini South Telescope in Chile. "The infrared spectrum of J0034 confirmed that we had found a very cool brown dwarf," said Dr. Sandy Leggett of Gemini Observatory. "However, it wasn't until we made a detailed study of the water steam and methane features, and compared them to other brown dwarf spectra, that we realized we had the coolest dwarf ever seen." The final piece of the puzzle -- precisely determining J0034's distance accurately by using its apparent motion due to parallax as the Earth moves in its orbit -- will have to wait for a year or so. However, astronomers expect to find that it is about 50 light-years away. This is closer to Earth than many of the stars that can be seen with the naked eye, and leaves open the exciting prospect of finding additional, even cooler objects lurking in our solar neighborhood. According to Mortlock, finding the correct distance is important. "The model brown dwarf spectra, from which we make some of our inferences about the temperature and other properties of J0034, is probably 'incomplete', in the sense that not all the effects of the molecules in the brown dwarf's atmosphere are included fully," he said. "Thus, getting a completely independent distance measure (and hence an independent luminosity) is an important final check to make sure that J0034 has the size and temperature we think it does." J0034 was discovered in the UKIDSS survey's First Data Release (DR1), which covers only five per cent of the final survey area. Combined with the discovery of a number of hotter brown dwarfs in the same data, this implies that UKIDSS will likely discover even more exotic objects as it continues its census of the coolest stars in the solar neighborhood. "Fully bridging the gap between stars and planets is one of the key aims of the UKIDSS survey, and it's wonderful to see these aims starting to be fulfilled at such an early stage of the survey program," said Dr. Andy Adamson, Associate Director of UKIRT. UKIDSS is expected to be completed by 2012, by which time it will have covered almost a quarter of the sky and hopefully further explored the cool, low-mass objects that are defined somewhere between stars and planets. Images
The discovery image of the sky showing the brown drwarf J0034 (the greenish spot marked by the arrow) with a number of (more distant) stars around it. The image was made from UKIRT data by using UKIDSS wavebands Y, J and H images as red, green and blue to make a false colour image. The discovery image was made as part of the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) on Mauna Kea in Hawai'i.
The GNIRS spectrum of brown dwarf J0034, showing the broad absorption features (large troughs) and indicating the regions covered by the UKIDSS Y, J, H and K bands. The spectroscopic observations were made using the Gemini Near-Infrared Spectrograph at Gemini South on Cerro Pachon in Chile.
Notes for EditorsBackground Information on Brown DwarfsThe reason that brown dwarf ULAS J0034-00 is causing a stir is because there is a boundary between what is considered a brown dwarf and what is considered a high-mass planet. The characterization of this brown dwarf is an important step toward pinning down that threshold. A brown dwarf is a small, faint, cool object (often called "failed" star) that, unlike the Sun and other stars, does not have sufficient mass to achieve hydrogen fusion in its core. With mostly slow gravitational contraction as an internal energy source, a brown dwarf gradually cools down as it radiates energy away into space over billions of years. Brown dwarfs exist in the mass range between about ten times that of Jupiter and one-twelfth the Sun's mass (which marks the boundary between these dwarfs and hydrogen-burning stars). The low temperatures and small sizes of brown dwarfs combine to make them both very faint and red in color. Most of their radiation is in the infrared, and therefore is not detectable to either the human eye or conventional optical detectors. Detectors sensitive to longer infrared wavelengths, such as those used at UKIRT and Gemini, are capable of observing these objects in unique ways. The spectrum of a brown dwarf is characterized by large wavelength regions from which almost no light is seen because it is being absorbed by water, methane and other molecules in the object's atmosphere. The details of these absorption patterns depend sensitively on the star's temperature. A careful analysis of J0034's absorption spectrum (along with some further color data obtained from the Spitzer Space Telescope) is what revealed it to have such a low temperature (between 600 K and 700 K). General Notes
UKIRTThe United Kingdom Infrared Telescope (UKIRT) with its 3.8-metre (12.5-foot) mirror is the world's largest telescope dedicated solely to infrared astronomy. The telescope is located near the summit of Mauna Kea, Hawaii, at an altitude of 4194 metres (13760 feet) above sea level. It is operated by the Joint Astronomy Centre in Hilo, Hawaii, on behalf of the UK Science and Technology Facilities Council. More about the UK Infrared Telescope: http://outreach.jach.hawaii.edu/articles/aboutukirt/ The UK ATCThe UK Astronomy Technology Centre is located at the Royal Observatory, Edinburgh (ROE). It is a scientific site belonging to the Science and Technology Facilities Council. The mission of the UK ATC is to support the mission and strategic aims of the Science and Technology Facilities Council and to help keep the UK at the forefront of world astronomy by providing a UK focus for the design, production and promotion of state of the art astronomical technology. Science and Technology Facilities CouncilThe Science and Technology Facilities Council is an independent, non-departmental public body of the Office of Science and Innovation which itself is part of the Department of Trade and Industry. It was formed as a new Research Council on 1 April 2007 through a merger of the Council for the Central Laboratory of the Research Councils (CCLRC) and the Particle Physics and Astronomy Research Council (PPARC) and the transfer of responsibility for nuclear physics from the Engineering and Physical Sciences Research Council (EPSRC). Is is one of seven national research councils in the UK. The Science and Technology Facilities Council is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Organisation for Nuclear Research, CERN, the European Space Agency and the European Southern Observatory. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility. Gemini ObservatoryThe Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located at Mauna Kea, Hawai'i (Gemini North) and the other telescope at Cerro Pachon in central Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space. More about Gemini Observatory: http://wwww.gemini.edu The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Science and Technology Facilities Council, the Canadian National Research Council (NRC), the Chilean Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq). The Observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership. Media ContactsPlease note that it is best to contact these individuals by email.
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