  56 UMa is a wide binary system that contains a chemically peculiar red giant
and a faint companion. Due to its surface chemical abundances, the red giant
was classified as a barium (Ba) star. This implies that the companion has to be
a white dwarf, since Ba stars form when mass is transferred to them from an
s-process rich Asymptotic Giant Branch (AGB) star. However, in the case of 56
UMa, the companion might be too massive to be the progeny of an AGB star that
efficiently produced s-process elements such as barium. In this Letter, we
revisit the orbital parameters of the system and perform a full spectral
analysis with the goal of investigating the Ba-star classification of the giant
and unravelling the nature of its faint companion. We combined radial-velocity
and astrometric data to refine the orbital parameters of the system, including
the orbital inclination and the companion mass. Then, we re-determined the
stellar parameters of the giant and its chemical abundances using
high-resolution HERMES spectra. Finally, we investigated the morphology of the
interstellar gas in the vicinity of the system. The faint component in 56 UMa
has a mass of $1.31 \pm 0.12$ M$_{\odot}$, which, together with the mixed s+r
abundance profile of the red giant, confirms that the giant is not a standard
barium star. Additionally, the clear identification of a cavity surrounding 56
UMa could indicate that a supernova explosion occurred about 10 5 years ago in
the system, suggesting that the faint companion might be a neutron star.
However, finding an evolutionary scenario that explains all the observables is
not trivial, so we discuss different possible configurations of the system and
their respective merits.
