  Core convection and dynamo activity deep within rotating A-type stars of 2
solar masses are studied with 3--D nonlinear simulations. Our modeling
considers the inner 30% by radius of such stars, thus capturing within a
spherical domain the convective core and a modest portion of the surrounding
radiative envelope. The MHD equations are solved using the ASH code to examine
turbulent flows and magnetic fields, both of which exhibit intricate time
dependence. By introducing small seed magnetic fields into our progenitor
hydrodynamic models rotating at one and four times the solar rate, we assess
here how the vigorous convection can amplify those fields and sustain them
against ohmic decay. Dynamo action is indeed realized, ultimately yielding
magnetic fields that are in energy equipartion with the flow. Such magnetism
reduces the differential rotation obtained in the progenitors, partly by
Maxwell stresses that transport angular momentum poleward and oppose the
Reynolds stresses in the latitudinal balance. In contrast, in the radial
direction we find that the Maxwell and Reynolds stresses may act together to
transport angular momentum. The central columns of slow rotation established in
the progenitors are weakened, with the differential rotation waxing and waning
in strength as the simulations evolve. We assess the morphology of the flows
and magnetic fields, their complex temporal variations, and the manner in which
dynamo action is sustained. Differential rotation and helical convection are
both found to play roles in giving rise to the magnetic fields. The magnetism
is dominated by strong fluctuating fields throughout the core, with the
axisymmetric (mean) fields there relatively weak.
