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Astronomers have produced a new spectral atlas of massive, hot stars in the Magellanic Clouds, small sister galaxies on the periphery of our galaxy, the Milky Way. The atlas is being presented for the first time on January 7 at a Washington, D.C., meeting of the American Astronomical Society.
The O-type stars featured in the atlas are young, bright, short-lived powerhouses that are among the most important engines driving the evolution of galaxies and the cosmos. Astronomers discovered in 1967 that O stars are so luminous that they "can't quite hold it together, and continuously blow off their outer layers," according to Alex Fullerton, a lead author of the new spectral atlas.
The atlas is based on observations of O stars made with the Far Ultraviolet Spectroscopic Explorer (FUSE), an orbiting observatory operated by The Johns Hopkins University for NASA. Fullerton is an astronomer from the University of Victoria in Canada, stationed at Johns Hopkins as Canadian support astronomer for FUSE. He said FUSE's abilities to observe emissions in the far ultraviolet were ideal for detecting the spectral signatures, known as P Cygni lines, of outflows of surface material from the O stars.
Using data from the new atlas, astronomers created charts that highlight the P Cygni profiles of a variety of different ions. The strength of those profiles vary with the stars’ temperatures, which progress vertically down the charts from hottest to coolest.
Nolan Walborn, an astronomer at the Space Telescope Science Institute who is also a lead author of the atlas, said it will help astronomers seeking to analyze O stars.
"It's a real zoo out there," said Walborn of the complex variety of star types confronting astronomers. "You have to sort out the phenomenology so you know what sorts of questions to ask about these stars and their life cycles."
The FUSE mission is a joint venture between NASA and the space agencies of Canada and France. Other contributors to the atlas are Paul Crowther and Allan Willis (University College London), Luciana Bianchi (JHU), John Hutchings (Herzberg Institute of Astrophysics, Canada), Derck Massa (Emergent IT/GSFC), Anne Pellerin (U. Laval, Canada), and George Sonneborn (NASA's GSFC).
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[NOTE TO EDITORS: The charts mentioned in this release are available at http://www.jhu.edu/news_info/news/home02/jan02/0star.html]