3D pyCloudy modelling of bipolar planetary nebulae: Evidence for fast fading of the lobes

Abstract

Aims. The origin and evolution of the shapes of bipolar planetary nebulae are poorly understood. We postulate that their history can be traced through their internal velocity fields in a procedure similar to the one well established for spherical objects. Such an analysis requires 3D photoionization and kinematical modelling that is computationally very time consuming. We apply an axially symmetric pseudo-3D photoionization model, pyCloudy, to derive the structures of six bipolar nebulae and two suggested post-bipolars in an attempt to constrain the bipolar planetary nebulae evolution. Methods. HST images and VLT/UVES spectroscopy are used for the modelling. The targets are located in the direction of the Galactic bulge. A 3D model structure is used as input to the photoionization code in order to fit the HST images. Line profiles of different ions constrain the velocity field. The model and associated velocity fields allow us to derive masses, velocities, and ages. Results. The 3D models find much lower ionized masses than required in 1D models: ionized masses are reduced by factors of 2-7. The selected bi-lobed planetary nebulae show a narrow range of ages: the averaged radii and velocities result in values between 1300 and 2000 yr. The lobes are fitted well with velocities that increase linearly with radius. These Hubble-type flows have been found before, and suggest that the lobes form at a defined point in time. The lobes appear to be slightly younger, by ∼500 yr, than the main (host) nebulae; they seem to form at an early phase of PN evolution and fade after 1-2 kyr. We find that 30-35% of bulge PNe pass through a bipolar phase.

The Herschel Planetary Nebula Survey (HerPlaNS): A Comprehensive Dusty Photoionization Model of NGC6781

“…Assuming V exp (AGB) = 16 − 22 km s −1 (corresponding to the observed expansion velocity of the cold CO gas, Bachiller et al 1993;Bergstedt 2015), V exp (today) = 12 km s −1 (from the [N ii] line; Arias & Rosado 2002), and R IB = 55 ′′ (the ion-ization front radius), the dynamical age would be roughly 7100 − 8600 yrs. Gesicki et al (2016) suggested t dyn ≃ (5/7) × (R IB /V exp ) based on hydrodynamical model calculations. Adopting V exp = 12 km s −1 as above, the hydrodynamical age would be 7140 yrs.…”

Photoionization models of Planetary Nebulae

“…The effect of the geometry on the determination of the velocity fields from line profiles have been studied by Morisset & Stasinska (2008). By fitting imaging with 3D models and high resolution profiles with expansion velocities Gesicki et al (2016) determine dynamical properties of 8 PNe. One must notice the long standing effort of the Potsdam group to develop hydrodynamical photoionization models: emission line profiles are used by Schönberner et al (2014) to constrain 1D models of the expansion properties and the internal kinematics of PNe.…”

Morphology and ionization characteristics of planetary nebulae PB 1 and PC 19

“…This is in line with the fact that higher percentage of nebula is covered by the slit during our observation of PC 19 compared to PB 1. More observations at different slit positions and a 3D photoionization model (e.g., Gesicki et al 2016) may help to yield more precise results.…”