  HD5550 is a spectroscopic binary composed of two A stars observed with Narval
at TBL in the frame of the BinaMIcS (Binarity and Magnetic Interactions in
various classes of Stars) Large Program. One component of the system is found
to be an Ap star with a surprisingly weak dipolar field of ~65 G. The companion
is an Am star for which no magnetic field is detected, with a detection
threshold on the dipolar field of ~40 G. The system is tidally locked, the
primary component is synchronised with the orbit, but the system is probably
not completely circularised yet. This work is only the second detailed study of
magnetic fields in a hot short-period spectroscopic binary. More systems are
currently being observed with both Narval at TBL and ESPaDOnS at CFHT within
the BinaMIcS project, with the goal of understanding how magnetism can impact
binary evolution and vice versa.
