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Stormy Weather on the Coolest Brown Dwarfs(Images and contact details at bottom of page) Astronomers have seen the first ever signs of cloudy weather on the coolest known brown dwarfs. These brown dwarfs are giant balls of gas similar to the planet Jupiter, which are not quite massive enough to become stars. The new observations were presented at the International Astronomical Union conference held in Hawaii in May 2002. Canadian astronomers from the Université de Montréal monitored the infrared radiation from brown dwarfs over many months with the 1.6-metre telescope at the Observatoire du Mont-Mégantic (OMM). They detected variations which are probably caused by the motion of clouds on their surface, like the stormy Great Red Spot of Jupiter, or temperature changes like the dark spots on our own Sun. Dr. René Doyon of the Université de Montréal said "this variability phenomenon in brown dwarfs will allow us to understand their atmospheres better, and help us investigate giant planets outside our own Solar System." Brown dwarfs bridge the gap between stars and giant planets. Unlike stars, they have insufficient mass to ignite nuclear reactions in their cores. As a result, they are extremely faint in visible light, and emit most of their energy as infrared radiation, beyond the range of the human eye. Even more recent observations have been made both at OMM and at other telescopes as far afield as Hawaii, the continental USA, Chile, Spain (the Canaries), France, and India by the international CLOUDS project (Continuous Longitude Observations of Ultra-cool Dwarfs). Today in Albuquerque, NM, at the 200th meeting of the American Astronomical Society (AAS), Dr. Bertrand Goldman presents the first results from this project (Poster 92.01). In April astronomers looked at one of the brown dwarfs, named SDSS J1254-0122, with the United Kingdom Infrared Telescope (UKIRT) atop Mauna Kea, on the Big Island of Hawaii. Dr. Sandy Leggett of UKIRT said "These clouds are made of substances such as silicates, like giant sandstorms in the atmosphere. UKIRT has shown that this brown dwarf is varying in brightness at several different infrared wavelengths, or colours. The exciting thing is that the colour changes aren't quite what we expect from our theories, so we need to investigate these fascinating objects further." Prof. Eduardo Martín of the Institute for Astronomy, University of Hawaii, member of the CLOUDS collaboration, led the simultaneous observations of the brown dwarfs using five different telescopes (UKIRT, University of Hawaii 88-inch, IRTF, Gemini and Keck) on Mauna Kea. "We are confirming the variability detected by our Canadian colleagues, and we have obtained additional information that will help to pin down the regions in the atmosphere where the light variations are originating. These objects are so cool and magnetically inactive that weather patterns are a plausible explanation for interpreting the data. Weather in brown dwarfs is probably more violent than in giant planets because the dwarfs have more dynamical atmospheres" said Dr. Martín. Images and notes for editors
Brown dwarfs:Brown dwarfs are intriguing objects, intermediate between stars and planets. Often described as 'failed stars', they are more massive than Jupiter, the largest planet in our Solar System, but they fall short of the minimum mass a true star needs --- 8% of our Sun's mass. Stars can shine constantly for billions of years because they generate nuclear energy from the fusion of hydrogen into helium. But brown dwarfs cannot sustain nuclear power production. After a modest initial flush, they cool off and become progressively fainter. The T-type brown dwarfs found to date are the coolest such objects so far detected. Their surface temperatures range down from about 1000 K to 800 K (700 to 500 degrees C). Their spectra show strong absorption by methane and water. Observatoire du Mont-Mégantic:The Observatoire du Mont-Mégantic is about 250 kilometers east of Montréal. Its 1.6-metre telescope is situated on Mont-Mégantic at an altitude of 1111 meters. It is operated jointly by the Université de Montréal and Université Laval and funded by the National Science and Engineering Research Council of Canada and Fonds Québécois de Recherche sur la Nature et les Technologies. More information: http://www.astro.umontreal.ca/omm/ United Kingdom Infrared Telescope:The world's largest telescope dedicated solely to infrared astronomy, the 3.8-metre UK Infrared Telescope (UKIRT) is sited near the summit of Mauna Kea, Hawaii, at an altitude of 4194 meters above sea level. It is operated by the Joint Astronomy Centre in Hilo, Hawaii, on behalf of the UK Particle Physics and Astronomy Research Council. More information: http://outreach.jach.hawaii.edu/articles/aboutukirt/ CLOUDS:The CLOUDS project (Continuous Longitude Observations of Ultra-cool Dwarfs) is an international collaboration aimed at studying variability in brown dwarfs over multiple time zones, in visible light and in infrared radiation. Its members include astronomers from Canada, France, India, Spain, UK and USA. American Astronomical Society meeting, 2-6 June 2002:The results are presented in poster 92.01: "CLOUDS, Continuous Longitude Observations of Ultracool DwarfS". Contact Dr. Bertrand Goldman, who is attending the meeting, for further information. Contact details:
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