A spatiokinematic study of the planetary nebula ngc 4361: Evidence for quadrupolar flows

Spatiokinematic observations were made on the planetary nebula (PN) NGC 4361 in the [OIII] lambda 5007 line using an imaging Fabry-Perot spectrometer. A large majority of the line profiles show centroidal asymmetry that flips over two distinct axes. The presence of the two symmetry axes is interpreted as evidence for quadrupolar flows that can be produced by a precessing equatorial disk. Model profiles generated from a generalized two-dimensional synthetic emission-line profile code for the proposed morphological model match the observed profiles quite well. The interlobe time lapse and the precession period of the progenitor are estimated. It is argued that NGC 4361 differs from the other known quadrupolar PNs in its chemical evolution and its galactic location. Assuming that the shell is heated by shocks due to the fast-moving lobes, we calculate a temperature increment of similar to 5000 K at the interface, which is in broad agreement with the temperature jump reported by Liu.