2011ApJ...740...27K

The morphology of the Red Rectangle (RR) exhibits several singular attributes. Most prominent are a series of linear features perpendicular to the symmetry axis which appear as "ladder rungs" across the nebula. At the edge of each "rung" gas seemingly flows from bright knots in a parabolic shape toward the center of the nebula. We present a new model of the RR which explains these features as a projection effect of the more common concentric arcs seen in other proto-planetary nebulae (e.g., Egg Nebula). Using the three-dimensional morpho-kinematic modeling software SHAPE, we have created a model of the RR that consists of spherical shells evacuated by a bi-conical outflow. When the symmetry axis is oriented perpendicular to the line of sight, the spherical shells become linear, thereby reproducing the "rungs" seen in the RR. When oriented at different inclinations, the linear features become spherical as observed in the Egg Nebula. The model also accurately reproduces the bright knots and the parabolic outflows from these knots that have proven difficult to explain in the past. Using this model, we are able to place a lower limit on the speed of the outflow of ∼158 km/s.