mass function

The mass function is a numerical relation between the masses of the two components of a spectroscopic binary that provides information on the relative masses of the two stars when the spectral lines of only one component can be seen. If Mp is the mass of primary (whose spectrum is known), Ms is the mass of secondary, and i is the inclination of the orbit, the mass function is given by (Ms3 sin3i) / (Mp + Ms)2.