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 FIRST CANADIAN SCIENCE DISCOVERIES WITH FUSE: HOW STARS RECYCLE MATERIAL IN DIFFERENT GALAXIES(January 12, 2000, Victoria, BC) -- HOT STAR WINDS - The Far Ultraviolet Spectroscopic Explorer (FUSE) orbiting telescope has uncovered evidence that shows how the most massive stars recycle their material differently in different galaxies. This in turn helps understand how galaxies evolve over cosmic time. Two Canadian organizations -- the National Research Council (NRC) and the Canadian Space Agency (CSA) -- are involved in FUSE science. FUSE is a unique new tool for studying stellar winds as it enables us to see how different parts of the wind are moving off the star. These particular spectral lines are found only at FUSE far-UV wavelengths. The most massive stars are so bright that they are blowing themselves apart. Such stars are more than a million times brighter than the sun, but live only one thousandth as long. A phenomenon, known as a stellar wind, blows away a large fraction of the star's initial mass during its brief 10 million year lifetime. Stellar winds have been known since the 1960s, when the outflowing material was detected moving away at up to 3000 km/s (some 11 million km/h). Stellar winds not only affect the fate of these massive stars, but they set the upper limit to their brightness before they blow themselves apart. They are also a major way in which new elements created by the nuclear reactions that power the stars, are cycled back into space, enriching the gas that will form later generations of stars. 
This drawing illustrates a stellar wind. The intense starlight pushes matter away from the star's surface. The matter accelerates and cools as it rises, until it leaves the star at high velocity. The hot matter moves slowly and cooler matter moves faster. 
It has also been found more recently that stellar winds blow more slowly off the hot stars in our two small neighbouring galaxies, the Magellanic Clouds [LMC: Large Magellanic Cloud; SMC: Small Magellanic Cloud], than in our own Galaxy. This indicates that there are global differences between galaxies and the way that their stars work, which we don't understand. 
This sketch illustrates how we view a stellar wind. Our telescope is off to the right. Between us and the star's surface, we see matter moving towards us that absorbs the starlight and leaves telltale dips in the spectrum of the light from the star's surface. At the same time, matter in the wind moving in other directions emits light which appears to be added to the basic starlight. Just where the dips and extra light are seen, tells us the wind's speed and structure, and where the material is. 
The result appears in the FUSE data as the sketched traces show. The horizontal line is the basic starlight level. On the left we see slow moving material as a sharp dip and extra peak. We measure outflow speed as a shift to the left. The fast-moving wind parts show up as dips further to the left, and a broader speed range in the extra light. 
This shows the first observations, which reveal conspicuous differences, never seen before, in the way material is blown off identical stars in the two galaxies. We see very different outflow velocities in the same material in the two stars. (The sharp dips arise in material not associated with the star so that the wind signal is sketched above them.) (1 million miles corresponds to about 1.6 million kilometers). Astronomers have started calculating how these differences can be explained, using many such pairs of features in the FUSE data. Thus, we are on our way to understanding why stars behave differently in different galaxies. This in turn tells us how the first stars in primeval galaxies began the process of enriching their galaxies, and affecting later generations of stars we see today. These first results show that the wavelengths unique to the FUSE instrument do indeed provide key information on Stellar Winds: large differences are seen between stars of the same mass in two different galaxies. We are a big step nearer understanding one of the major energy sources that moulded our galaxy. We have waited many years for FUSE to open up this new window on stellar evolution. Canadian Involvement in FUSE ScienceJohn Hutchings of NRC's Herzberg Institute of Astrophysics (HIA) is a member of the FUSE science team, and leads the team program on this topic. Other team members involved in the work are NRC's Don Morton, and Alex Fullerton and Pierre Chayer (Canadian mission support astronomers stationed at Johns Hopkins University - JHU, with funding from the Canadian Space Agency - CSA), and astronomers at JHU, University of Colorado, NASA, and University College London (UK). The stellar winds under investigation were independently discovered by Don Morton and John Hutchings in the 1960s. FUSE thus serves long-standing research interests of NRC scientists. In addition to the science team research, Canadian scientific proposals are guaranteed at least 10% of guest investgator time on FUSE, and many Canadians have approved programs that will be carried out this year. Canadian Involvement in FUSE InstrumentationThe FUSE project is a joint mission between NASA, the Canadian Space Agency, and the Centre National d'Etudes Spatiales - CNES of France. CSA provided the Fine-Error Sensors (FES), a fine guidance system that points the telescopes to a precision of 0.2 arc sec, necessary for the ultraviolet instrumentation on FUSE. The FES were designed by a team at NRC's HIA in Victoria (optical design by Chris Morbey, detector development and software design by Rick Murowinski and Tim Hardy). The detailed design and flight hardware were completed by COM DEV International of Cambridge, Ontario, under contract to the Canadian Space Agency. The NRC team has worked closely with CSA and COM DEV at all stages of the project. FUSE is a NASA Expolorer Mission, funded in cooperation with the Canadian Space Agency and the Centre National d'Etudes Spatiales of France. FUSE was developed and is being operated for NASA by the Johns Hopkins University in collaboration with the University of California, Berkeley and the University of Colorado. For more on the FES camera onboard FUSE, click on the NRC Press Release September 1998. NRC has the mandate to operate and administer astronomical observatories established by the Government of Canada. NRC exercises this mandate through HIA, which provides astronomical facilities, research and infrastructure to university scientists and their students. HIA has fostered many international partnerships and is renowned worldwide for its development of leading-edge instruments and software. For more information on Canadian FUSE Science, please contact: Dr. John Hutchings, Principal Research Officer
Dr. Jacques P. Vallée, Media Officer/Senior Astronomer, |
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