  The proto-planetary Red Rectangle nebula is powered by HD 44179, a
spectroscopic binary (P = 318 d), in which a luminous post-AGB component is the
primary source of both luminosity and current mass loss. Here, we present the
results of a seven-year, eight-orbit spectroscopic monitoring program of HD
44179, designed to uncover new information about the source of the
Lyman/far-ultraviolet continuum in the system as well as the driving mechanism
for the bipolar outflow producing the current nebula. Our observations of the
H-alpha line profile around the orbital phase of superior conjunction reveal
the secondary component to be the origin of the fast (max. v~560$ km s$^{-1}$)
bipolar outflow in the Red Rectangle. The variation of total H-alpha flux from
the central H II region with orbital phase also identifies the secondary or its
surroundings as the source of the far-ultraviolet ionizing radiation in the
system. The estimated mass of the secondary (~0.94 M$\sun$) and the speed of
the outflow suggest that this component is a main sequence star and not a white
dwarf, as previously suggested. We identify the source of the
Lyman/far-ultraviolet continuum in the system as the hot, inner region
(T$_{max} \ge 17,000$ K) of an accretion disk surrounding the secondary, fed by
Roche lobe overflow from the post-AGB primary at a rate of about $2 -
5\times10^{-5}$ M$\sun$ yr$^{-1}$. The total luminosity of the accretion disk
around the secondary is estimated to be at least 300 L$\sun$, about 5% of the
luminosity of the entire system. (abridged)
