Binary Stars Palomar Observatory Star Systems Star systems

Binary Stars Palomar Observatory

Star Systems • Star systems can involve both single and multiple stars. – Double stars common • Star systems within 10 Pc have been cataloged by RECONS (Mar 2018). – – – Total systems 317 Singles 232 Doubles 66 Triples 14 Quadruples 3 Quintuples 2

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.

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.

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

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.

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

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