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Office of Marketing & Media Relations
University of California-Riverside

News Media Contact:
Iqbal Pittalwala
Phone: 909.787.2645
Email: iqbal{at}citrus.ucr.edu

Additional contacts:
Steve Howell, UC Riverside
steve.howell{at}ucr.edu

Thomas Harrison, New Mexico State University
tharriso{at}nmsu.edu

May 26, 2003

Astronomers show that low-mass stars in binary stars appear to behave 
like high-mass, evolved stars

RIVERSIDE, Calif. -- Astronomers Steve Howell of the University of 
California, Riverside and Thomas E. Harrison and Heather Osborne of
New Mexico State University have found from their observations of
over a dozen mass-losing stars in 'cataclysmic variables' that most
of the secondary stars do not appear to be normal main sequence stars
in terms of their apparent abundances. To various degrees, each star
seems to have low to no carbon and other odd mixtures of elements
such as sodium and calcium, the astronomers announced today at the
American Astronomical Society meeting in Nashville, Tenn.

(A main sequence star is a star that is in its normal state, such as
the sun. These stars have well-defined relations between luminosity,
temperature, size and mass.)

"Cataclysmic variables are binary stars consisting of a white dwarf 
primary and a lower mass secondary star," explained Howell. A binary 
star system consists of two stars orbiting about their common center
of mass and held together by their mutual gravitational attraction. A
white dwarf is a star that has exhausted all its nuclear fuel and
has collapsed to a very small size, about the size of the Earth.

Howell further explained that the high gravity of the white dwarf
pulls matter off the lower-mass, but larger secondary star. This
material often forms a disk around the white dwarf. The orbital
periods of these binaries are short, typically ranging from
approximately 12 hours to 80 minutes. "Cataclysmic variables are very
small systems," he said. "The entire binary would completely fit
inside our sun." 

For their research, the three astronomers used telescopes to obtain 
spectral observations of mass-losing stars in cataclysmic variables. 
"Our findings suggest that the normal idea that 'main sequence' rules 
apply to the mass-losing stars appears not to be the case," said
Howell. "Furthermore, the observed abundance patterns are consistent
with stellar material formed by a process called CNO or
carbon-nitrogen-oxygen burning, which is only thought to occur in
stars with masses greater than those of the mass-losing stars.

The research, funded by the National Science Foundation, was
performed in the past two years using telescopes located at the Kitt
Peak National Observatory, near Tucson, Ariz., and on Mauna Kea,
Hawaii, using the NASA infrared telescope (IRTF) and the United
Kingdom infrared telescope (UKIRT).

Related Links:

* Institute of Geophysics and Planetary Physics, UC Riverside
  http://www.igpp.ucr.edu/
* College of Natural and Agricultural Sciences, UC Riverside
  http://www.cnas.ucr.edu/

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