  We investigate the dynamic evolution of gaseous region around FS~CMa
post-mergers. Due to the slow rotation of a central B-type star, the dynamics
is driven mainly by the magnetic field of the central star. Recent observations
have allowed us to set a realistic initial conditions such as, the magnetic
field value ($B_\star\approx6\times10^{3}G$), the mass of the central star
($M_\star=6M_\odot$), and the initial disc density
$\rho_{d0}\in[10^{-13}\mathrm{g\,cm^{-3}},10^{-11}\mathrm{g \, cm^{-3}}] $. We
use the PLUTO code to perform 2.5D-MHD simulations of thin and thick discs
models. Especially relevant for the interpretation of the observed properties
of FS~CMa post-mergers are the results for low-density discs, in which we find
formation of a jet emerging from inner edge of the disc, as well as the
formation of the so called "hot plasmoid" in the corona region. Jets are
probably detected as discrete absorption components in the resonance lines of
FS~CMa stars. Moreover, the magnetic field configuration in the low-density
plasma region, favors the appearance of magnetocentrifugal winds from the disc.
The currents toward the star created by the magnetic field may explain
accidentally observed material infall. The disc structure is significantly
changed due to the presence of the magnetic field. The magnetic field is also
responsible for the formation of a hot corona as observed in several FS~CMa
stars through the Raman lines. Our results are valid for all magnetic stars
surrounded by a low density plasma, i.e., some of stars showing the B[e]
phenomenon.
