High-velocity regions in planetary nebulae
Gesicki K., Zijlstra A.A., 2003, MNRAS, 338, 347
The internal velocity fields of planetary nebulae are studied with a
resolution of 5\,km\,s$^{-1}$. We analyze deep echelle spectra from
three nebulae in the Bulge, the Sagittarius Dwarf and the SMC. No
effects of metallicity is seen, except possibly a slower onset of the
fast wind from the central star. Robust evidence is found for the
existence of a high-velocity shock at the inner edges of the nebulae.
Such a shock is predicted in hydrodynamical models but had not
previously been observed. The shock gas is accelerated by the fast
wind from the central star. A similar shock at the outer edges traces
the expansion of the ionized shell into the ambient AGB wind.
Evidence for localized regions of high velocity is also found from
lines of intermediate exciation, for two of nebulae. We explore
several possible interpretations: (1) an embedded shock at
intermediate radii, as predicted by hydrodynamic models at the
position of the outer edge of the swept-up inner shell; (2) deviations
form spherical symmetry, where in some directions the
intermediate-excitation lines extend into the region of the outer
shock; (3) An intermediate swept-up shell, as seen in some Galactic
planetary nebulae. The remaining nebula, with a [WC] star, shows
strong turbulence. This may trace a superposition of many embedded
shock-lets. We suggest a relation to the time-variable [WC] wind,
giving a planetary nebula subjected to a multitude of sound waves.
paper (pdf, MNRAS reprint, 531k)
Last update: Jan 10, 2003