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 \sim 560 km s ^ { -1 } ) bipolar outflow in the Red Rectangle .
The outflow was previously inferred on the basis of a single , broad H \alpha emission line profile .
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 ( \sim 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 } \geq 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 \times 10 ^ { -5 } M \sun yr ^ { -1 } .
The speed of the accretion-driven , bipolar outflow was found to be strongly modulated by the inter-component separation in the highly eccentric ( e = 0.37 ) orbit , with maximum speeds occurring near periastron and minimum speeds found around apastron .
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 .