The origin of runaway stars

Milliarcsecond astrometry provided by Hipparcos and by radio observations makes it possible to retrace the orbits of some of the nearest runaway stars and pulsars to determine their site of origin. The orbits of the runaways AE Aurigae and mu Columbae and of the eccentric binary iota Orionis intersected each other similar to2.5 Myr ago in the nascent Trapezium cluster, confirming that these runaways were formed in a binary-binary encounter. The path of the runaway star zeta Ophiuchi intersected that of the nearby pulsar PSR J1932 + 1059, similar to1 Myr ago, in the young stellar group Upper Scorpius. We propose that this neutron star is the remnant of a supernova that occurred in a binary system that also contained zeta Oph and deduce that the pulsar received a kick velocity of similar to 350 km s(-1) in the explosion. These two cases provide the first specific kinematic evidence that both mechanisms proposed for the production of runaway stars, the dynamical ejection scenario and the binary-supernova scenario, operate in nature.