  We investigate the formation mechanism for the observed nearly polar aligned
(perpendicular to the binary orbital plane) debris ring around the eccentric
orbit binary 99 Herculis. An initially inclined nonpolar debris ring or disc
will not remain flat and will not evolve to a polar configuration, due to the
effects of differential nodal precession that alter its flat structure.
However, a gas disc with embedded well coupled solids around the eccentric
binary may evolve to a polar configuration as a result of pressure forces that
maintain the disc flatness and as a result of viscous dissipation that allows
the disc to increase its tilt. Once the gas disc disperses, the debris disc is
in a polar aligned state in which there is little precession. We use
three-dimensional hydrodynamical simulations, linear theory, and particle
dynamics to study the evolution of a misaligned circumbinary gas disc and
explore the effects of the initial disc tilt, mass, and size. We find that for
a wide range of parameter space, the polar alignment timescale is shorter than
the lifetime of the gas disc. Using the observed level of alignment of 3 deg.
from polar, we place an upper limit on the mass of the gas disc of about 0.014
M_sun at the time of gas dispersal. We conclude that the polar debris disc
around 99 Her can be explained as the result of an initially moderately
inclined gas disc with embedded solids. Such a disc may provide an environment
for the formation of polar planets.
