The mass-ratio distribution of visual binary stars

The present effort to arrive a realistic statistical distribution of the mass-ratio q = M(secondary)/M(primary) investigates the selection effects governing the observations of visual binary stars on the basis of a numerical simulation code which 'generates' binary stars and 'looks' at them to establish whether a terrestrial observer would be capable of detecting them. It is found that the mass-ratio distribution observed for main-sequence systems can be accounted for by a distribution of secondary masses according to the initial mass function (IMF), where phi(M) is proportional to M to the -2.7th power. Numerical simulations of biased sampling show that the q-distribution derived from the Orbits of Visual Binaries catalog is incompatible with the distribution of secondary masses according to the IMF. (O.C.)