# 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 *M*_{p} is the mass of primary (whose spectrum
is known), *M*_{s} is the mass of secondary, and *i* is
the inclination of the orbit, the mass function is given by (*M*_{s}^{3} sin^{3}i) / (*M*_{p} + *M*_{s})^{2}.