PHYS 183 Lecture Notes - Lecture 16: Sirius, Binary Star, Starflight

• School: McGill University
• Department: Physics
• Course: PHYS 183
• Professor: Gilbert Holder

Document Summary

Astronomers first measure apparent brightness of stars but apparent brightness depends on distance. Want to measure intrinsic parameters: luminosity, temperature, distance, mass. Previous lectures: how to get distance (parallax), compute luminosity, use spectra to get temperatures. 1804 william herschel found castor orbits a fainter star. Do a careful study of distribution of stars on sky, see many are very close to other stars. Binary system: two stars orbit each other. Multiple system: several stars orbit each other. Our sun is a single star, oh well. 2/3 of all stars are in binary/multiple systems. Visual binaries: we observe both stars directly. Astrometric binaries: see (cid:862)(cid:449)o(cid:271)(cid:271)le(cid:863) of a star (cid:271)ut (cid:272)a(cid:374)"t see 2nd star. Composite spectrum binaries: observe one star but it has spectral lines from 2 different spectral types. Eclipsing binaries: light gets periodically dimmer and brighter. Spectroscopic binaries: spectral lines of a star oscillate periodically about their average wavelength.