Shaping planetary nebulae by light jets

Akashi, Muhammad; Soker, Noam

doi:10.1111/j.1365-2966.2008.13935.x

Cited by 45 publications

(62 citation statements)

References 49 publications

(97 reference statements)

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“…The initial AGB-wind densities employed are always very low (typical values correspond toṀ agb ≈ 10 −6 M yr −1 ) so that thermal pressure is dynamically unimportant (see, e.g., Akashi & Soker 2008). However, as we have mentioned above, typical PN structures require final AGB-wind mass-loss rates of about 10 −4 M yr −1 , higher by about two orders of magnitude than assumed in current jet modelling.…”

Section: Discussionmentioning

confidence: 99%

The evolution of planetary nebulae

Schönberner

Jacob

Sandín

et al. 2010

A&A

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Aims. By means of hydrodynamical models we do the first investigations of how the properties of planetary nebulae are affected by their metal content and what can be learned from spatially unresolved spectrograms of planetary nebulae in distant stellar systems. Methods. We computed a new series of 1D radiation-hydrodynamics planetary nebulae model sequences with central stars of 0.595 M surrounded by initial envelope structures that differ only by their metal content. At selected phases along the evolutionary path, the hydrodynamic terms were switched off, allowing the models to relax for fixed radial structure and radiation field into their equilibrium state with respect to energy and ionisation. The analyses of the line spectra emitted from both the dynamical and static models enabled us to systematically study the influence of hydrodynamics as a function of metallicity and evolution. We also recomputed selected sequences already used in previous publications, but now with different metal abundances. These sequences were used to study the expansion properties of planetary nebulae close to the bright cut-off of the planetary nebula luminosity function. Results. Our simulations show that the metal content strongly influences the expansion of planetary nebulae: the lower the metal content, the weaker the pressure of the stellar wind bubble, but the faster the expansion of the outer shell because of the higher electron temperature. This is in variance with the predictions of the interacting-stellar-winds model (or its variants) according to which only the central-star wind is thought to be responsible for driving the expansion of a planetary nebula. Metal-poor objects around slowly evolving central stars become very dilute and are prone to depart from thermal equilibrium because then adiabatic expansion contributes to gas cooling. We find indications that photoheating and line cooling are not fully balanced in the evolved planetary nebulae of the Galactic halo. Expansion rates based on widths of volume-integrated line profiles computed from our radiation-hydrodynamics models compare very well with observations of distant stellar system. Objects close to the bright cut-off of the planetary nebula luminosity function consist of rather massive central stars (>0.6 M ) with optically thick (or nearly thick) nebular shells. The halfwidth-half-maximum velocity during this bright phase is virtually independent of metallicity, as observed, but somewhat depends on the final AGB-wind parameters. Conclusions. The observed expansion properties of planetary nebulae in distant stellar systems with different metallicities are explained very well by our 1D radiation-hydrodynamics models. This result demonstrates convincingly that the formation and acceleration of a planetary nebula occurs mainly because of ionisation and heating of the circumstellar matter by the stellar radiation field, and that the pressure exerted by the shocked stellar wind is less important. Determinations of nebular abundances by means of photoionisa...

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Section: Discussionmentioning

confidence: 99%

The evolution of planetary nebulae

Schönberner

Jacob

Sandín

et al. 2010

A&A

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“…The mass loss rate of the FFS jets and speed were chosen to meet FFS launched by a WD. The SMW jets formed by such FFS jets can have v SMW ≃ 500 km s −1 andṀ SMW ≃ 10 −6 M ⊙ yr −1 , and can lead to the formation of some bipolar PNs (Akashi 2007;Akashi & Soker 2008). As in the previous section I substitute δ = 1.…”

Section: The Constraints On the Fast First Stage (Ffs) Jetsmentioning

confidence: 99%

“…Wide jets were considered (Soker 2004a) and simulated (Akashi 2007;Akashi & Soker 2008) for inflating fat bubbles in PNs in a process similar to that in clusters of galaxies. In some PNs the motion of the nebula is ballistic, i.e., the outflow velocity of different nebular segments is proportional to their distance from the center (e.g., Sanchez Contreras et al 2006).…”

Section: Introductionmentioning

confidence: 99%

The formation of slow-massive-wide jets

Soker

2008

New Astronomy

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I propose a model for the formation of slow-massive-wide (SMW) jets by accretion disks around compact objects. This study is motivated by claims for the existence of SMW jets in some astrophysical objects such as in planetary nebulae (PNs) and in some active galactic nuclei in galaxies and in cooling flow clusters. In this model the energy still comes from accretion onto a compact object. The accretion disk launches two opposite jets with velocity of the order of the escape velocity from the accreting object and with mass outflow rate of ∼ 1−20% of the accretion rate as in most popular models for jet launching; in the present model these are termed fast-first-stage (FFS) jets. However, the FFS jets encounter surrounding gas that originates in the mass accretion process, and are terminated by strong shocks close to their origin. Two hot bubbles are formed. These bubbles accelerate the surrounding gas to form two SMW jets that are more massive and slower than the FFS jets. There are two conditions for this mechanism to work. Firstly, the surrounding gas should be massive enough to block the free expansion of the FFS jets. Most efficiently this condition is achieved when the surrounding gas is replenished. Secondly, the radiative energy losses must be small.

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“…As a result, instead of spherical fast winds as in the generalized interacting stellar wind (GISW) model (see, e.g., review by Balick & Frank 2002), collimated fast winds (CFWs) have been proposed to operate during the post-AGB phase (and even earlier during the late AGB phase), and be the primary agents for the shaping of PPNs and young PNs (Sahai & Trauger 1998;Sahai 2001). CFW models have been used to account for the morphology and kinematics of a few well-studied PPNs and PNs, with some assuming a radial wind with a small opening angle (Lee & Sahai 2003, hereafter Paper I; Akashi & Soker (2008), some assuming a cylindrical jet either unmagnetized (Cliffe et al 1995;Steffen & López 1998;Guerrero et al 2008) or magnetized (Lee & Sahai 2004), and some assuming a bullet (a massive clump) along the outflow axis (Dennis et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Collimated Fast Wind in the Preplanetary Nebula CRL 618

Lee

Hsu

Sahai

2009

ApJ

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Collimated fast winds (CFWs) have been proposed to operate during the post asymptotic giant branch (post-AGB) evolutionary phase (and even earlier during the late AGB phase), responsible for the shaping of preplanetary nebulae (PPNs) and young planetary nebulae (PNs). This paper is a follow-up to our previous study of CFW models for the well-studied PPN CRL 618. Previously, we compared our CFW models with optical observations of CRL 618 in atomic and ionic lines and found that a CFW with a small opening angle can readily reproduce the highly collimated shape of the northwestern (W1) lobe of CRL 618 and the bowlike structure seen at its tip. In this paper, we compare our CFW models with recent observations of CRL 618 in CO J = 2-1, J = 6-5, and H 2 1-0 S(1). In our models, limb-brightened shell structures are seen in CO and H 2 at low velocity (LV) arising from the shocked AGB wind in the shell, and can be identified as the LV components in the observations. However, the shell structure in CO J = 2-1 is significantly less extended than that seen in the observations. None of our models can properly reproduce the observed high-velocity (HV) molecular emission near the source along the body of the lobe. In order to reproduce the HV molecular emission in CRL 618, the CFW is required to have a different structure. One possible CFW structure is the cylindrical jet, with the fast wind material confined to a small cross section and collimated to the same direction along the outflow axis.

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Shaping planetary nebulae by light jets

Cited by 45 publications

References 49 publications

The evolution of planetary nebulae

The evolution of planetary nebulae

The formation of slow-massive-wide jets

Collimated Fast Wind in the Preplanetary Nebula CRL 618

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