The Riddle of the Red Rectangle

Abstract

I reconsider my study (Icke 1981) of the hydrodynamic mechanism that is responsible for the shape of the Red Rectangle. The density of this nebula is so high, and the central star(s) so cool, that momentum driven outflow is almost guaranteed. Focusing of a spherically symmetric stellar wind through an inner shock creates a biconical pattern that may be responsible for the characteristic X-shape of the outer nebula. I compute the evolution of periodic biconical outflow. Observations made available to me by Van Winckel can thus be modeled in great detail. Features that I initially thought to be problematic for my interpretation, such as the occurrence of intersecting shocks on the symmetry axis, turned out to be present on closer inspection of the Hα image.