Line ratios from shocked cloudlets in planetary nebulae

Abstract

Context. Some PNe and PPNe show compact knots, travelling at high velocities away from the central sources.Aims. We compute a number of models from which we obtain predictions of the emission-line spectrum, which can be compared with the spectra of the observed knots. Methods. We completed a series of 11 axisymmetric simulations of an initially spherical cloudlet, travelling away from a photoionizing source, into a uniform medium. The simulations included a multi-frequency transfer of the ionizing radiation, and a 33 species non-equilibrium ionization network. Results. From our simulations, we computed emission maps and spatially-integrated emission-line spectra. The predictions show a transition from spectra similar to those of shock wave models (for simulations with lower photoionization rates) to spectra similar to those of photoionized regions (for simulations with higher photoionization rates). Conclusions. The spectra from our photoionized cloudlet models have a range of line ratios that agree approximately with the observed spectra when shown in two-line ratio diagnostic diagrams. The predicted and observed spatial distributions of the emission (with high ionization lines extending more towards the source than lower ionization lines) agree in a qualitative way.

Binary planetary nebulae nuclei towards the Galactic bulge

“…ner gap and elongation in the N-S direction closely mirrors the elliptical shape and cross-section of the gap in Model A. We interpret the ionisation structure of the 'ears' or 'multiple-shells' referred to by previous authors as shocked outflows similar to IC 4634 and M 3-16 (Raga et al 2008; Sec. 4.5.1).…”

“…These features are well-reproduced by models as fastmoving photo-ionised neutral clumps (Raga et al 2008). The [NII] image of M 3-16 also reveals low-ionisation filaments and some knots which do not display the same high degree of point symmetry as in IC 4634.…”

“…Observationally K 1-2 and M 3-16 fit the model with the signature 'reverse bow-shock' ionisation structure in their polar outflows (e.g. IC 4634, Raga et al 2008). The counterparts in e.g.…”

“…Raga, Steffen & González 2005). Polar outflows are better described by fast-moving neutral material interacting again with a photo-ionising wind (Raga et al 2007(Raga et al , 2008. Observationally K 1-2 and M 3-16 fit the model with the signature 'reverse bow-shock' ionisation structure in their polar outflows (e.g.…”

STIS optical spectroscopy of the lobes of CRL 618

“…These diagrams also give information on the excitation mechanism (photoionization, shock excitation or mixed). In this figure we have adapted these diagrams including the most recent compilation of HH objects (Raga et al 1996), a sample of proto-PNe (Raga et al 2008) and the irradiated shock models from the work of Raga et al (2008). The PN region is adopted from Riesgo & López (2006 Raga et al 1996) are shown as black dots.…”