Les systèmes binaires à mouvement propre commun.

The study of common proper-motion binary systems, characterized by expanding orbits and periods of the order of several hundred thousand years, is discussed. Factors which have an impact on the orbits of these systems include mass loss (acting on time intervals of the order of 12 million years) and distant passing stars and molecular clouds (acting on scales of time of the order of the age of the Galaxy). It is pointed out that determination of the maximal size of these systems would make possible the measurement of hidden mass in the Galactic disk.