The binary nature of the barium stars. II - Velocities, binary frequency, and preliminary orbits

A series of radial velocity observations has been obtained over the last 3 years of a sample of 20 Ba II stars. Seventeen of these (85%) are found to show long-term velocity variations ranging in amplitude from a few to tens of km s⁻¹. Thus it seems likely that all Ba II stars are binary systems. An additional Ba ii star in the open cluster NGC 2420 is also found to have a variable velocity. Orbits for seven Ba II stars indicate low-mass companions, compatible with their being white dwarfs. Separations are large, about 2 AU on average. The peculiar abundances are not explained, but the fact remains that multiplicity must bear a causal relationship to these peculiarities.