Dirk%20Terrell

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Binary Stars

• Dirk Terrell
• Southwest Research Institute
• terrell_at_boulder.swri.edu

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Why Bother with Binaries?

• Provide accurate data that are very difficult to
  determine for single stars such as masses and
  radii.
• Are very common- the majority of stellar systems
  are binaries.
• They are interesting objects in and of
  themselves. Still many puzzles to solve about
  their structure and evolution.

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Visual Binaries
The two stars are resolved, so we see the orbital
motion directly. Interferometric techniques give
the same kind of data.
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Spectroscopic Binaries
Single-lined spectroscopic binary spectral lines
of one star are visible.
Double-lined spectroscopic binary spectral lines
of both stars are visible.
Dan Durda http//www.boulder.swri.edu/durda/
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X-ray Binaries
Pulses from the neutron star act as a clock and
can be used to measure the orbit.
Mark Garlick - http//space-art.co.uk/
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Eclipsing Binaries
Binary orbital plane is oriented so that the two
stars pass in front of one another as seen from
Earth. The light curve is rich in information
about the two stars.
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Wide Variety of Light Curves
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Algols
High-mass stars evolve faster than low mass
stars But in Algols the less massive star is
evolved. How is that possible? Mass transfer! The
low mass star was once the more massive star,
evolved, and dumped matter onto the other star,
eventually reversing the mass ratio.