The evolution of planetary nebulae

Abstract

Abstract. We investigate and discuss the expansion properties of planetary nebulae by means of 1D radiation-hydrodynamics models computed for different initial envelope configurations and central star evolutionary tracks. In particular, we study how the expansion depends on the initial density gradient of the circumstellar envelope and show that it is possible to derive information on the very last mass-loss episodes during the star's final evolution along and off the asymptotic giant branch. To facilitate the comparison of the models with real objects, we have also computed observable quantities like surface brightness and emission-line profiles. With the help of newly acquired high-resolution emission-line profiles for a sample of planetary nebulae we show that models with initial envelopes based on the assumption of a stationary wind outflow fail to explain the observed expansion speeds of virtually all of the observed planetary nebulae. Instead it must be assumed that during the very last phase of evolution along the final asymptotic giant branch evolution the mass-loss rate increases in strength, resulting in a much steeper slope of the circumstellar radial density distribution. Under these conditions, the expansion properties of the nebular gas differ considerably from the self-similar solutions found for isothermal conditions. Furthermore, the mass loss must remain at a rather high level until the stellar remnant begins to evolve quickly towards the central star regime. Current theoretical computations of dust-driven mass-loss which are restricted to rather low temperatures cannot be applied during the star's departure from the asymptotic giant branch.

The central star of the planetary nebula PB 8: a Wolf-Rayet-type wind of an unusual WN/WC chemical composition

“…Schönberner et al 2005b;Miller Bertolami & Althaus 2007 flux of the model is diluted by its distance, which we consider to be a free parameter, as no certain distance is known. With the help of Eq.…”

The H surface brightness-radius relation: a robust statistical distance indicator for planetary nebulae

“…These tracks were generated from the hydrodynamical nebular models of Perinotto et al (2004) and Schönberner et al (2005a) along with the CSPN, using the evolutionary tracks for the latter from Blöcker (1995) and Schönberner (1981). The nebular radius and surface brightness for PNe with a range of core masses were then overplotted on the SHα-r plane in Fig.…”

Astrophysics in 2005

“…That's what they are best at, and the details depend on metallicity (Marshall et al 2004), or only on luminosity and temperature, not on composition (van Loon et al 2005), or on luminosity, radius, mass, temperature, and surface gravity (Schroeder & Cuntz 2005), which is probably enough parameters to take care of what might really be extra radiation pressure on grains when there are more metals to condense. 50 Garcia-Segura et al (2005) believe that magnetic fields are also important in driving the higher-speed collimated winds, though we and Schoenberner et al (2005) endorse a prolonged, low velocity superwind as the main mass stealer. In any case, stripping goes so deep that the layer seen can briefly be as hot as 200,000 K (Werner & Drake 2005 for H1504ϩ65 and a number of new candidates).…”