28/07/2004 – Auditório Principal Bloco G – IAG/USP

Dra. Denise R. Gonçalves

Instituto de Astrofísica de Canárias – Espanha

Título/Title: Low-Ionization Structures in PNe: The Peculiar Excitation of K 4–47

Resumo/Abstract:

The morphology and kinematics of jets and knots of low-ionization (LIS) can be reasonably explained by the interplay between the stellar AGB and post-AGB winds or between stellar and disc winds. LIS originated by this interplay are predicted to be highly supersonic (likely to be shock-excited), highly collimated and two-sided. For single stars, LIS are expected to be produced at the same time as the main PN shell; for a binary star, they may be younger than the host PN. However, important properties of jets and knots seem harder to explain, since LIS do not have an important density contrast with respect to the PN main components, and most LIS systems studied so far are mainly photoionized. K 4–47 is particularly interesting to further investigate these issues because, unlike most of the LIS studied up to now, its pair of knots is mainly shock-excited.

Long-slit medium-resolution spectra of K 4-47, an unusual planetary nebula composed of a compact high-ionization core and a pair of low-ionization knots, are analyzed. Assuming photoionization from the central star, we have derived physical parameters for all the nebular components, and the (ICF) chemical abundances of the core, which appear similar to Type-I PNe for He and N/H but significantly deficient in oxygen. The nebula has been further modelled using both photoionization (CLOUDY) and shock (MAPPINGS) codes.

From the photoionizatin modelling of the core, we find that both the strong auroral [OIII]4363Å and [NII]5755Å emission lines observed and the optical size of the core cannot be accounted for, if a homogeneous density is adopted. We suggest that strong density stratification, matching the high-density core detected at radio wavelengths and the much lower density of the optical core, might solve the problem. From the bow-shock modelling of the knots, on the other hand, we find that knots' chemistry is also represented by Type-I PN abundances, and that they would move with velocities of 250–300 km/s.

 

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