SCI238 Lecture Notes - Main Sequence, Stellar Evolution, Cosmic Distance Ladder
9 Jul 2013
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How do we measure stellar masses? (binary stars) Newton"s version of kepler"s third law: applied only when we can observe one object orbiting another, and it requires that we measure both the orbital period and the average orbital distance of the orbiting object. Binary star systems systems in which two stars continually orbit one another. Other times we see a set of shifting lines from only one star because its companion is too dim to be detected (a single-lined spectroscopic binary): blueshifted: star approaching us. Measuring masses in binary systems: apply newton"s version of kepler"s third law only if we can measure both the orbital period and the separation of the two stars. Orbital period: observe how long each orbit takes: visual binaries: period determined form motion of one star about the other, eclipsing binary: we measure the time between eclipses in an eclipsing binary we observe periodic changes brightness: eclipses. Amplitude => orbital scale amplitude ratio => mass ratio.
