A connection between the rate of rotation of interstellar clouds, magnetic fields, ambipolar diffusion, and the periods of binary stars.
Observations do not show any interstellar clouds rotating much faster than the Galaxy. This can be attributed to magnetic braking, which the observed parameters of the interstellar medium show to be very efficient as long as the magnetic field is frozen in the matter. The critical density ncr at which the field decouples from the matter determines the period of rotation of a binary star system, assumed to form by a collapsing (nearly nonmagnetic) fragment that conserves its angular momentum. The observed periods Tb of binary stars (roughly 100 yr > Tb > 10 hr) may be accounted for if ncr ranges from 7.5 x l0 to 2.2 x 106 , respectively. We reexamine the process of ambipolar diffusion (by appropriately scaling the field strength to dense-cloud densities) and show that, at the above densities, it can decouple the field from the matter within 8.8 x l0 -3.9 x 10 years. A scenario for star formation is outlined. Subject headings: interstellar: matter - magnetic fields - stars: binaries - stars: formation