scholarly journals Morphology of Planetary Nebulae—Possible Effects of Rotation on Stellar Ejecta

2004 ◽  
Vol 215 ◽  
pp. 473-478
Author(s):  
Sun Kwok
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Time Variable ◽  
Asymptotic Giant Branch ◽  
Stellar Winds ◽  
Spherically Symmetric ◽  
Fast Wind ◽  
Effects Of Rotation ◽  
Slow Wind ◽  
Kinematic Properties

Planetary nebulae are formed as the result of the interaction between a slow stellar wind from the asymptotic giant branch progenitor and a later-developed fast outflow from the central star. Many of the morphological and kinematic properties of planetary nebulae have been successfully explained by this interacting stellar winds model. The observed diverse morphologies of planetary nebulae can also be understood if the slow wind is not spherically symmetric. However, new observational features such as collimated outflows and multi-polar lobes suggest that the fast wind may be non-isotropic and time variable. The possible roles of magnetic fields and rotation may play in the formation of these features are discussed.

scholarly journals Photoionisation effects in hydrodynamical simulations of planetary nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 350-351
Author(s):  
L. Hernández-Martínez ◽  
D. Estrella ◽  
P. F. Velázquez ◽  
A. Esquivel ◽  
A. C. Raga
Keyword(s):  
Proper Motion ◽  
Planetary Nebulae ◽  
Numerical Results ◽  
Accelerated Expansion ◽  
Central Source ◽  
Fast Wind ◽  
Hα Emission ◽  
Hydrodynamical Simulations ◽  
Slow Wind

AbstractWe explored the photoionisation effects on both the proper motion and emission of planetary nebulae NGC 6302, by means of hydrodynamical simulations. We used the GUACHO code, which includes the photoionisation due to central source (Esquivel et al. 2009, Esquivel & Raga 2013). We model these PNe considering an interacting stellar fast wind with and ejected toroidally shaped slow wind (Uscanga et al. 2014). Synthetic Hα emission maps were obtained from our numerical results in order to do a comparison between the cases with and without photoionisation. Using a wavelets fittering method on our results for the ionisation case, we do not find an increase in the proper motion velocities, however we can see an accelerated expansion in both cases. For the ionisation case the Hα emission presents an increase.

scholarly journals Effect of ambient wind velocity on Planetary Nebula morphology

1997 ◽  
Vol 180 ◽  
pp. 224-224
Author(s):  
Vikram V. Dwarkadas ◽  
Roger A. Chevalier ◽  
John M. Blondin
Keyword(s):  
Wind Velocity ◽  
Ambient Medium ◽  
Asymptotic Giant Branch ◽  
Density Contrast ◽  
Expansion Velocity ◽  
Ambient Wind ◽  
Pn Velocity ◽  
Fast Wind ◽  
Self Similar ◽  
Slow Wind

Planetary Nebulae (PNe) are formed by the interaction of the fast wind from a post-Asymptotic Giant Branch Star with the slow ambient wind from a previous epoch. If the two interacting winds have constant properties, the velocity of the PN shell tends towards a constant with time and the shape becomes self-similar. Additionally, if the velocity of the fast wind is much higher than the expansion velocity of the shell, the interior of the hot shocked bubble becomes isobaric. Using semi-analytical methods, complemented by hydrodynamic simulations, we have calculated the shapes of PNe in the self-similar stage (Dwarkadas et al. 1996). We have investigated the contribution of the ambient wind velocity to PN morphology, which has hitherto not received much attention since the work of Kahn & West (1985). We find that the nebular morphology is a consequence of the density contrast between pole and equator in the ambient medium, the steepness of the density profile and the velocity of the ambient wind; classification of PNe purely on the basis of the first two factors may be misleading. In particular, the ratio of ambient wind velocity to PN velocity is important in determining whether the nebula shows a bulge or a cusp at the equator. A high density contrast coupled with a low velocity for the external medium gives rise to extremely bipolar nebulae. For large density contrasts and a significant value of the slow wind velocity, the surface density maximum of the shell shifts away from the equator, giving rise to peanut-shaped structures with pronounced equatorial bulges. As long as the external wind velocity is small compared to the expansion velocity of the nebula, the PNe tend to be more bipolar, even with a moderate density contrast. If the PN velocity is close to that of the external wind, the shape is relatively spherical. However, inclusion of an asymmetric velocity profile in the slow wind, with the velocity increasing towards the pole, can lead to a bipolar nebula if the equatorial velocity is sufficiently low. Preliminary results with a slow wind velocity increasing towards the equator (as is found in calculations of common envelope evolution) show that the nebulae tend to be more oblate, which is not often observed in nature. Representative results for shapes of PNe using various values of the relevant parameters are presented.

scholarly journals Models of Planetary Nebulae: Generalisation of the Multiple Winds Model

1989 ◽  
Vol 131 ◽  
pp. 411-424 ◽  
Author(s):  
F. D. Kahn
Keyword(s):  
Planetary Nebula ◽  
High Speed ◽  
Planetary Nebulae ◽  
Central Star ◽  
Theoretical Description ◽  
Basic Theory ◽  
Spectral Lines ◽  
High Excitation ◽  
General Shape ◽  
Fast Wind

According to the multiple winds model a planetary nebula forms as the result of the interaction of a fast wind from the central star with the superwind that had previously been emitted by the progenitor star. The basic theory which deals with the spherically symmetrical case is briefly summarised. Various improvements are then considered in turn. A better history is clearly needed of the way that the central star becomes hotter, it is unrealistic to make the assumption that the superwind is spherically symmetrical, and finally there are likely to be important instabilities at some of the interfaces in the PN, notably that between the shocked superwind and the HII layer. These changes in the theoretical description produce a better understanding of the conditions in the outer parts of a PN and of the nature of its general shape, and they should lead to an explanation for the occurrence of high speed motions, and of highly ionized species and high excitation spectral lines.

On the morphology and internal kinematics of PNe

1997 ◽  
Vol 180 ◽  
pp. 184-189
Author(s):  
A. Manchado
Keyword(s):  
Stellar Evolution ◽  
Great Degree ◽  
Planetary Nebula ◽  
High Density ◽  
Stellar Winds ◽  
Low Density ◽  
Fast Wind ◽  
Slow Wind

The study of the morphology of planetary nebula (PN) is fundamental for addressing several questions in the context of stellar evolution. An AGB star can loose most of its mass due to strong stellar winds. Kwok et al. (1978) proposed that the interaction of a low-density fast wind with a high-density slow wind, will form the PN. This model can account for the round observed PNe with a great degree of symmetry. However as we will see later, round PNe are not the most common ones. Therefore a mechanism for causing asymmetry has to be invoked. Several processes have been proposed by different authors.

scholarly journals A Speculation into the Origin of Neutral Globules in Planetary Nebulae: Could the Helix’s Comets Really be Comets?

1995 ◽  
Vol 12 (2) ◽  
pp. 170-173
Author(s):  
Grant Gussie
Keyword(s):  
Solar System ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Central Star ◽  
Oort Cloud ◽  
Asymptotic Giant Branch ◽  
Neutral Gas ◽  
Red Giant ◽  
The Masses

AbstractA novel explanation for the origin of the cometary globules within NGC 7293 (the ‘Helix’ planetary nebula) is examined, namely that these globules originate as massive cometary bodies at large astrocentric radii. The masses of such hypothetical cometary bodies would have to be several orders of magnitude larger than those of any such bodies observed in our solar system in order to supply the observed mass of neutral gas. It is, however, shown that comets at ‘outer Oort cloud’ distances are likely to survive past the red giant and asymptotic giant branch evolutionary phases of the central star, allowing them to survive until the formation of the planetary nebula. Some observational tests of this hypothesis are proposed.

scholarly journals X-ray Studies of Planetary Nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 104-108
Author(s):  
Rodolfo Montez
Keyword(s):  
Mass Transfer ◽  
Planetary Nebulae ◽  
Central Star ◽  
Electromagnetic Spectrum ◽  
Stellar Winds ◽  
X Ray ◽  
New Directions ◽  
Multi Wavelength ◽  
Formation And Evolution ◽  
Compact Sources

AbstractX-ray emission from planetary nebulae (PNe) provides unique insight on the formation and evolution of PNe. Past observations and the ongoing Chandra Planetary Nebulae Survey (ChanPlaNS) provide a consensus on the two types of X-ray emission detected from PNe: extended and compact point-like sources. Extended X-ray emission arises from a shocked “hot bubble” plasma that resides within the nebular shell. Cooler than expected hot bubble plasma temperatures spurred a number of potential solutions with one emerging as the likely dominate process. The origin of X-ray emission from compact sources at the location of the central star is less clear. These sources might arise from one or combinations of the following processes: self-shocking stellar winds, spun-up binary companions, and/or accretion, perhaps from mass transfer, PN fallback, or debris disks. In the discovery phase, X-ray studies of PNe have mainly focused on the origin of the various emission processes. New directions incorporate multi-wavelength observations to study the influence of X-ray emission on the rest of the electromagnetic spectrum.

scholarly journals Historical overview of planetary nebulae research

2011 ◽  
Vol 7 (S283) ◽  
pp. 1-8
Author(s):  
Sun Kwok
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Evolutionary Status ◽  
Complex Molecules ◽  
Chemical Enrichment ◽  
Star Studies ◽  
The Galaxy ◽  
Underlying Causes

AbstractPlanetary nebulae (PNs) were first discovered over 200 years ago and our understanding of these objects has undergone significant evolution over the years. Developments in astronomical optical spectroscopy and atomic physics have shown that PNe are gaseous objects photoionized by UV radiation from a hot central star. Studies of the kinematics of the nebulae coupled with progress in theories of stellar evolution have led to the identification that PNe are evolved stars and progenitors of white dwarfs. Development of infrared and millimeter-wave technology in the 1970s made us realize that there is significant amount of neutral matter (molecules and dust) in PNe. The link of PNe to the stellar winds from their progenitor asymptotic giant branch (AGB) stars and subsequent dynamical interactions are now believed to be the underlying causes of the morphological structures of PNe. The role of PNe as prolific molecular factories producing complex molecules and organic solids has significant implications on the chemical enrichment of the Galaxy.In this paper, we discuss the misconceptions and errors that we have encountered in our journey of understanding the nature of PN. The various detours and dead ends that had happened during our quest to pin down the evolutionary status and causes of nebulae ejection will be discussed. As there are still many unsolved problems in PN research, these lessons of history have much to offer for future progress in this field.

scholarly journals H2 kinematics in Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 245-245
Author(s):  
Douglas M. Kelly ◽  
William B. Latter ◽  
Joseph L. Hora ◽  
Charles E. Woodward
Keyword(s):  
Radiation Field ◽  
Near Infrared ◽  
Planetary Nebulae ◽  
Central Star ◽  
Hydrodynamic Interactions ◽  
Fast Wind ◽  
Kinematic Studies ◽  
Red Giant ◽  
Vibration Rotation

The evolution of planetary nebulae is controlled largely by hardening of the radiation field from the central star and by hydrodynamic interactions between the “fast wind” and the slower red giant wind. These processes also result in the heating and dissociation of H2 and in the production of H2 vibration–rotation lines in the near-infrared. Both mechanisms tend to produce high gas temperatures and, at high densities, a thermal population of states. Kinematic studies provide vital information on the geometry and expansion of the nebulae and offer a discriminant between shocked and photodissociated regions.

scholarly journals Interferometric observations of OH and H2O masers in protoplanetary nebulae imaged with HST - A unique diagnostic of their spatial-kinematic structure

2002 ◽  
Vol 206 ◽  
pp. 352-357
Author(s):  
Raghvendra Sahai ◽  
Mark J. Claussen ◽  
Mark Morris
Keyword(s):  
High Speed ◽  
Current Model ◽  
Planetary Nebulae ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
High Angular Resolution ◽  
Sequence Evolution ◽  
Imaging Data ◽  
Circumstellar Material ◽  
Protoplanetary Nebulae

One of the most exciting challenge facing theories of post-main sequence evolution today is to understand how Asymptotic Giant Branch (AGB) stars transform themselves into aspherical planetary nebulae (PNe). Recently, high-resolution imaging surveys of young planetary nebulae and protoplanetary nebulae (PPNe: objects in transition between the AGB and PN phases) have revealed that the majority of these objects are characterised by multipolar bubbles distributed roughly point-symmetrically around the central star. These data strongly suggest that the current model for the shaping of PNe is no longer adequate. High angular-resolution kinematic information is sorely needed to complement the imaging data in order to test new hypotheses, such as our proposal that episodic high-speed jet-like outflows, operating during the protoplanetary or very late-AGB phase, are the primary agent.We have therefore begun a program of using interferometric mapping of OH (and H2O, when feasible) maser emission in order to trace the kinematics of the structures discovered in protoplanetary nebulae with HST. These masers provide a unique and crucial probe of the kinematics of the circumstellar material in PPNe, because of the lack of other emission-line diagnostics. Although our work is still in its infancy (only two objects have been studied in detail), we find that the OH masers indicate the presence of multiple low-latitude outflows and an increase of outflow velocity with latitude. This paper summarises our progress so far, the state of current studies, and future prospects.

scholarly journals Progenitors of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 401-410 ◽  
Author(s):  
Sun Kwok
Keyword(s):  
Mass Loss ◽  
Significant Role ◽  
Planetary Nebulae ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
The Past

Over the past decade, we have come to realize that mass loss on the asymptotic giant branch (AGB) plays a significant role in the formation of planetary nebulae (PN). Mass ejected during the AGB can now be observed in haloes of PN and we believe that the main shell of PN is formed by the interaction of this material with a later-developed central-star wind. In this review, we show that the evolution from AGB to PN can be traced in a continuous infrared sequence. This sequence predicts properties of proto-PN which allow them to be identified.

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