  AU Mon is a long-period (11.113 d) Algol-type binary system with a persistent
accretion disk that is apparent as double-peaked H-alpha emission. We present
previously unpublished optical spectra of AU Mon which were obtained over
several years with dense orbital phase coverage. We utilize these data, along
with archival UV spectra, to model the temperature and structure of the
accretion disk and the gas stream. Synthetic spectral profiles for lines
including H-alpha, H-beta, and the Al III and Si IV doublets were computed with
the Shellspec program. The best match between the model spectra and the
observations is obtained for an accretion disk of inner/outer radius 5.1/23
R_sun, thickness of 5.2 R_sun, density of 1.0e-13 g/cm^3, and maximum
temperature of 14000 K, along with a gas stream at a temperature of ~8000 K
transferring ~2.4e-9 M_sun/yr. We show H-alpha Doppler tomograms of the
velocity structure of the gas, constructed from difference profiles calculated
through sequentially subtracting contributions from the stars and accretion
structures. The tomograms provide independent support for the Shellspec
modeling, while also illustrating that residual emission at sub-Keplerian
velocities persists even after subtracting the disk and stream emission.
Spectral variability in the H-alpha profile beyond that expected from either
the orbital or the long-period cycle is present on both multi-week and
multi-year timescales, and may reflect quasi-random changes in the mass
transfer rate or the disk structure. Finally, a transient UV spectral
absorption feature may be modeled as an occasional outflow launched from the
vicinity of the disk-stream interaction region.
