HD271791: dynamical versus binary-supernova ejection scenario
  The atmosphere of the extremely high-velocity (530-920 km/s) early B-type
star HD271791 is enriched in $\alpha$-process elements, which suggests that
this star is a former secondary component of a massive tight binary system and
that its surface was polluted by the nucleosynthetic products after the primary
star exploded in a supernova. It was proposed that the (asymmetric) supernova
explosion unbind the system and that the secondary star (HD271791) was released
at its orbital velocity in the direction of Galactic rotation. In this Letter
we show that to explain the Galactic rest-frame velocity of HD271791 within the
framework of the binary-supernova scenario, the stellar remnant of the
supernova explosion (a $\la$ 10 Msun black hole) should receive an
unrealistically large kick velocity of $\geq$ 750-1200 km/s$. We therefore
consider the binary-supernova scenario as highly unlikely and instead propose
that HD271791 attained its peculiar velocity in the course of a strong
dynamical three- or four-body encounter in the dense core of the parent star
cluster. Our proposal implies that by the moment of encounter HD271791 was a
member of a massive post-supernova binary.
