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).