I propose a scenario for the formation of double-ring systems, as observed in some planetary nebulae and in the outer rings of SN 1987A. In this scenario, two jets, one jet on each side of the equatorial plane, expand into a thin, dense shell. Such a flow is expected in binary systems where the mass-losing primary undergoes an impulsive mass loss episode which forms a thin, dense shell. I assum...

Extragalactic surveys in the emission line of [O III] λ5007 have provided us with the absolute line strengths of large, homogeneous sets of planetary nebulae. These data have been used to address a host of problems, from the measurement of the extragalactic distance scale, to the study of stellar populations. I review our current understanding of the [O III] planetary nebula luminosity function...

We present maps at 20 00 resolution of the molecular emission around 18 evolved stars (14 asymptotic giant branch stars, one supergiant, two proto-planetary nebulae and one planetary nebula), mostly in the 12 CO(3-2) line. Almost all molecular envelopes appear to be at least marginally resolved at this resolution. A substantial fraction of the molecular envelopes show clear deviations from sphe...