Magnetic massive binary and multiple systems in open clusters and associations

The origin of the magnetism in massive O stars and the role the magnetic field
plays in their evolution remain unknown. However, the mass transfer in stellar
merging events might not only rejuvenate the mass gaining star, but induce
differential rotation, which can be a key ingredient to generate a magnetic
field. In agreement with this scenario, we have recently been able to show that
numerous components in massive binary and multiple systems possess detectable
magnetic fields, implying that multiplicity plays a defining role in the
generation of magnetic fields. The evolution of binary and multiple systems with
magnetic components is currently completely unexplored. Since almost all studied
systems with magnetic components belong to open clusters and associations, their
membership presents an obvious way to obtain their kinematic ages. Importantly,
most of these systems have rather short orbital periods, probably due to the
fact that massive systems play an important role for the dynamical evolution of
clusters, as they can serve as an energy exchange mechanism, leading to very
tight binaries and escaping cluster members. Another advantage of studying these
systems in clusters and associations is that the corresponding bulk metallicity
can be determined. In our presentation, we will discuss the most recent results
of our magnetic field measurements in detached, semi-detached, and overcontact
systems belonging to clusters and associations at different ages.