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Binary Stars Dirk Terrell Southwest Research Institute [email protected] 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. Visual Binaries The two stars are resolved, so we see the orbital motion directly. Interferometric techniques give the same kind of data. 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/ 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/ 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. Wide Variety of Light Curves 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.