Question

Consider a binary star system that has bright lines at 656.72 and 656.86 nm. Over the course of six months the 656.72-nm line moves to longer wavelength and the 656.86-nm line moves to shorter wavelength, until finally the two have swapped (i.e., the spectrum of the star system again shows bright lines at 656.72 and 656.86 nm). Assume that the stars are of roughly equal mass and moving in a circular orbit with axis perpendicular to the line connecting the star system to the earth.

Determine the mass M of each star.

Answer 1