  A rotating star with a monopole (or split monopole) magnetic field gives the
simplest, prototype model of a rotationally driven stellar wind. Winds from
compact objects, in particular neutron stars, carry strong magnetic fields with
modest plasma loading, and develop ultra-relativistic speeds. We investigate
the relativistic wind launched from a dense, gravitationally bound, atmosphere
on the stellar surface. We first examine the problem analytically and then
perform global kinetic plasma simulations. Our results show how the wind
acceleration mechanism changes from centrifugal (magnetohydrodynamic) to
electrostatic (charge-separated) depending on the parameters of the problem.
The two regimes give winds with different angular distributions and different
scalings with the magnetization parameter.
