SIMBAD references

We propose that the fast low-ionization features (FLIERS) observed in some planetary nebulae are recombination zones behind stationary supersonic recombination fronts produced in mass-loaded jets. The main physical characteristics can be reproduced by jets with opening angles of a few degrees and momentum fluxes of ∼ 10²⁸ g.cm.s^–2, which mass-load from embedded clumps in the nebular envelope. Very simple considerations based on inferred clump masses imply that the nebular envelope contains ∼ 600-60, 000 clumps. Although this range is wide, it is not incompatible with clump numbers estimated from observational data.