Mass-loaded jet models of fast low-ionization features in planetary nebulae

We propose that the fast low-ionization features (FLIERS) observed in some planetary nebulae are recombination zones behind stationary supersonic reco mbination fronts produced in mass-loaded jets, The main physical characteri stics can be reproduced by jets with opening angles of a few degrees and mo mentum fluxes of similar to 10(28)g Cm s(-2), which mass-load from embedded clumps in the nebular envelope. Very simple considerations based on inferr ed clump masses imply that the nebular envelope contains similar to 600-60 000 clumps. Although this range is wide, it is not incompatible with clump numbers estimated from observational data.