1. Binary Stars Palomar Observatory

2. Star systems within 10 Pc have been cataloged by RECONS (Jan 2012). Total systems 259 Singles 185 Doubles 55 Triples 15 Quadruples 3 Quintuples 1 Star Systems • Star systems can involve both single and multiple stars. • Double stars common

3. Visual Binaries • Visual binaries occur when the centers are separated by more than 1”. • Atmospheric effects • Apparent binaries occur when two stars are near the same coordinates but not close in space.

4. Orbit • Kepler’s third law is used as compared to the sun. • Mass M in solar masses • Period P in years • Semimajor axis a in AU • The semimajor axis depends on knowing the distance and tilt.

5. Mass • Gravity attracts each star towards the center of mass. • Larger mass closer to the center • Separate masses come from observing the center of mass. Magnified to show gravitational pull

6. Spectroscopic Binaries • As binary stars orbit each other their radial motion changes. • Doppler shift • Spectral lines shift red then blue • The period of time to make the shift and back is one orbital revolution.

7. Some stars are too close to separate with telescopes or spectra. Fluctuating spectrum Fluctuating light Periodic eclipses diminish the total light. Eclipsing Binaries

8. Stellar Sizes • The length of the eclipse is related to the size of the star. • A few close, big stars can be seen in a telescope as measurable disks. • Speckle interferometry Betelgeuse with infrared interferometry X. Haubois, Observatorie de Paris