OB-runaways as a result of massive star evolution.

We investigated four OB-associations and tried to model six runaways which were possibly ejected from these associations. From the position and space velocity of each runaway we tried to trace back its birthplace and birthdate in the subgroup of the parent association where the runaway started its space travel. We used massive star evolutionary results to check if all known parameters of the runaway star can be explained: its atmospheric hydrogen abundance and the fact that its position in the HRD, i.e. spectral type and luminosity is hit by the evolutionary track at the correct time. It is found that the runaway ζ Oph can be modeled only by the binary scenario, where the secondary was ejected after the SN event of its primary out of Upp Cen Lup. ζ Pup can be explained by single star evolution only when it was ejected from Vela R2, implying a luminosity that is significantly higher than commonly used. A binary scenario for ζ Pup can be found provided that the binary was a field star. The three runaways of Orion can be modeled by binary evolution with ejection from the subgroup Ori OB1a. For two of them, single star evolution with ejection from Ori OB1c works equally well. Finally, the OB-runaway optical component of Vela X-1 is still bound to its SN remnant and thus certainly a result of binary evolution. The system originated presumably in Vela OB1.