Describe the various ways that stellar masses can be determined in binary star systems

Question

What will be an ideal response?

Answer 1

In visual binary stars, we can determine their period and average separation by photos made over many years, and thus find their total mass with Kepler's third law, as revised by Newton. The more massive star stays closer to the center of mass, and moves slower, so we can find their actual masses in this division.
In spectroscopic binaries, we note the relative splitting of the two stars' Doppler shifted spectral lines, and again the faster moving star is the less massive. The period between two successive splits and recombinations of their lines gives us their period, and their speeds allow us to again find the sizes of their orbits, and the total mass of the pair.