"Multiplicity of CP stars and the nature of their companions"

Authors: S. Hubrig,  M. Schoeller, N. Ageorges  and O. Marco.

We discuss the results of our recent adaptive optics study of
multiplicity of B-type stars
exhibiting strong overabundances of the chemical elements Hg and Mn in
their atmospheres. A key point for the understanding of the abundance
patterns in these stars may be connected with binarity and multiplicity.
It is intriguing that more than half of the sample of HgMn stars studied
previously by speckle interferometry and recently using diffraction
limited near infrared imaging with NACO at the VLT belong to multiple
systems.
In some binary systems with an HgMn primary, the components definitely
rotate subsynchronously. It is remarkable that the majority of these
systems have more than two components. Probably the most
intriguing and most fundamental question is whether all B-type close
binaries with subsynchronously rotating companions belong to more
complex systems.
The most recent results of K-band spectroscopy with ISAAC of close
companions will also be presented