The kinematics of the permitted C II λ6578 line in a large sample of planetary nebulae.
RICHER M.G., SUAREZ G., LOPEZ J.A. and GARCIA DIAZ M.T.
Abstract (from CDS):
We present spectroscopic observations of the C ii λ6578 permitted line for 83 lines of sight in 76 planetary nebulae at high spectral resolution, most of them obtained with the Manchester Echelle Spectrograph on the 2.1 m telescope at the Observatorio Astronomico Nacional on the Sierra San Pedro Martir. We study the kinematics of the C ii λ6578 permitted line with respect to other permitted and collisionally excited lines. Statistically, we find that the kinematics of the C ii λ6578 line are not those expected if this line arises from the recombination of C2+ ions or the fluorescence of C+ ions in ionization equilibrium in a chemically homogeneous nebular plasma, but instead its kinematics are those appropriate for a volume more internal than expected. The planetary nebulae in this sample have well-defined morphology and are restricted to a limited range in Hα line widths (no large values) compared to their counterparts in the Milky Way bulge; both these features could be interpreted as the result of young nebular shells, an inference that is also supported by nebular modeling. Concerning the long-standing discrepancy between chemical abundances inferred from permitted and collisionally excited emission lines in photoionized nebulae, our results imply that multiple plasma components occur commonly in planetary nebulae.