scholarly journals Magnetic fields around AGB stars and Planetary Nebulae

2013 ◽  
Vol 9 (S302) ◽  
pp. 389-397 ◽  
Author(s):  
W. H. T. Vlemmings
Keyword(s):  
Magnetic Fields ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Heavy Elements ◽  
Current Evidence ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Significant Progress ◽  
Natural Explanation ◽  
Shaping Process

AbstractStars with a mass up to a few solar masses are one of the main contributors to the enrichment of the interstellar medium in dust and heavy elements. However, while significant progress has been made, the process of the mass-loss responsible for this enrichment is still not exactly known and forces beyond radiation pressure might be required. Often, the mass lost in the last phases of the stars life will become a spectacular planetary nebula. The shaping process of often strongly a-spherical PNe is equally elusive. Both binaries and magnetic fields have been suggested to be possible agents although a combination of both might also be a natural explanation.Here I review the current evidence for magnetic fields around AGB and post-AGB stars pre-Planetary Nebulae and PNe themselves. Magnetic fields appear to be ubiquitous in the envelopes of apparently single stars, challenging current ideas on its origin, although we have found that binary companions could easily be hidden from view. There are also strong indications of magnetically collimated outflows from post-AGB/pre-PNe objects supporting a significant role in shaping the circumstellar envelope.

scholarly journals Thermal Pulses and Planetary Nebula Ejection

1993 ◽  
Vol 155 ◽  
pp. 291-298 ◽  
Author(s):  
P.R. Wood ◽  
E. Vassiliadis
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Stellar Surface ◽  
Agb Stars ◽  
Theoretical Evolution ◽  
Thermal Pulses

Thermal pulses in AGB stars cause large luminosity variations at the stellar surface. The role of these luminosity variations in the production of planetary nebulae is discussed. Results of theoretical evolution calculations which include mass loss modulated by thermal pulses are presented.

scholarly journals AGBs, Post-AGBs and the Shaping of Planetary Nebulae

Galaxies ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 99 ◽  
Author(s):  
Eric Lagadec
Keyword(s):  
Angular Resolution ◽  
Hubble Space Telescope ◽  
Planetary Nebulae ◽  
High Angular Resolution ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Shaping Process ◽  
Huge Variety ◽  
Isotropic Radiation

During the last decades, observations, mostly with the Hubble Space Telescope, have revealed that round Planetary Nebulae were the exception rather than rule. A huge variety of features are observed, such as jets, discs, tori, showing that the ejection of material is not due to isotropic radiation pressure on a spherical shell and that more physics is involved. This shaping process certainly occur early in the evolution of these low and intermediate mass stars and must leave imprints in the evolutionary stages prior the PN phase. Thanks to news instruments on the most advanced telescopes (e.g., the VLTI, SPHERE/VLT and ALMA), high angular resolution observations are revolutionising our view of the ejection of gas and dust during the AGB and post-AGB phases. In this review I will present the newest results concerning the mass loss from AGB stars, post-AGB stars and related objects.

scholarly journals Energy Distribution of Planetary Nebulae (UV to Radio)

1993 ◽  
Vol 155 ◽  
pp. 99-108
Author(s):  
C.Y. Zhang
Keyword(s):  
Energy Distribution ◽  
Planetary Nebula ◽  
Spectral Energy Distribution ◽  
Planetary Nebulae ◽  
Central Star ◽  
Spectral Energy ◽  
Significant Progress ◽  
Dust Shell ◽  
The Past ◽  
Entire Wavelength Range

The past decade has seen significant progress in our understanding of spectral energy distribution of planetary nebulae over the entire wavelength range from UV to radio. In this review we show the detailed breakdown of the energy budget for a planetary nebula as a system of the three components, i.e., the central star, the gaseous nebula and the dust shell. This picture of the energy distribution is further discussed in the context of planetary nebula evolution.

Magnetic fields in PNe and other evolved low-mass and intermediate-mass stars

2016 ◽  
Vol 12 (S323) ◽  
pp. 136-140
Author(s):  
Laurence Sabin ◽  
Qizhou Zhang ◽  
Gregg A. Wade ◽  
Agnès Lèbre ◽  
Roberto Vázquez
Keyword(s):  
Magnetic Fields ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Efficient Mechanism ◽  
Intermediate Mass Stars ◽  
Low Mass

AbstractMagnetic fields are likely to be an efficient mechanism which can affect evolved intermediate mass stars (i.e. post-AGB stars and planetary nebulae) in different ways such as via the shaping of their envelope. However, observational probes for the presence of those fields are still scarce. I will present a summary of the works, including those from our group, on the detection and measurement of magnetic fields in various evolved objects.

scholarly journals Heavy elements in planetary nebulae: A theorist's gold mine

2011 ◽  
Vol 7 (S283) ◽  
pp. 127-130
Author(s):  
Amanda I. Karakas ◽  
Maria Lugaro
Keyword(s):  
Neutron Capture ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Heavy Elements ◽  
Gold Mine ◽  
Agb Stars ◽  
Capture Process ◽  
Wide Range ◽  
Model Predictions

AbstractObservations of planetary nebulae have revealed a wealth of information about the composition of heavy elements synthesized by the slow neutron capture process (the s process). In some of these nebulae the abundances of neutron-capture elements are enriched by factors of 10 to 30 times the solar value, indicating that these elements were produced in the progenitor star while it was on the asymptotic giant branch (AGB). In this proceedings we summarize results of our recent full s-process network predictions covering a wide range of progenitor masses and metallicities. We compare our model predictions to observations and show how this can provide important insights into nucleosynthesis processes occurring deep within AGB stars.

scholarly journals MHD Models of Planetary Nebulae: Review

2003 ◽  
Vol 209 ◽  
pp. 457-464 ◽  
Author(s):  
Guillermo García-Segura
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Ab Initio ◽  
Radiation Pressure ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Basic Question ◽  
Red Giants ◽  
Outer Envelope ◽  
Parent Star

When we discuss about MHD effects in planetary nebulae (PNe), there naturally arises a basic question: which magnetic field do we study? One possibility is the ISM magnetic field (e.g. Heiligman 1980), even more if we are concerned with moving PNe (e.g. Soker & Dgani 1997). The next possibility is the internal or stellar magnetic field (Gurzadian 1962). It is important to start this review by quoting Aller (1958): “It has been pointed out by Minkowski and others that the structural appearance of many planetary nebulae strongly suggest the presence of magnetic fields. It seems unlikely that such magnetic fields are produced ab initio in the nebular shell. Rather, they must have existed in the outer envelope of the parent star. Certain red giants stars with magnetic fields may evolve in such a way that the expansion of the shell is largely governed by the presence of such a field. Magnetic effects may actually be more important than gas pressure differentials and radiation pressure in controlling the evolution of a planetary nebula”.

scholarly journals Common Envelope Evolution: Implications for Post-AGB Stars and Planetary Nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 207-212 ◽  
Author(s):  
J. Nordhaus
Keyword(s):  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Common Envelope ◽  
Long Period ◽  
Short Period ◽  
Computational Work ◽  
Broad Interest

AbstractCommon envelopes (CE) are of broad interest as they represent one method by which binaries with initially long-period orbits of a few years can be converted into short-period orbits of a few hours. Despite their importance, the brief lifetimes of CE phases make them difficult to directly observe. Nevertheless, CE interactions are potentially common, can produce a diverse array of nebular shapes, and can accommodate current post-AGB and planetary nebula outflow constraints. Here, I discuss ongoing theoretical and computational work on CEs and speculate on what lies ahead for determining accurate outcomes of this elusive phase of evolution.

scholarly journals Magnetic fields and radio emission processes in maser-emitting planetary nebulae

2017 ◽  
Vol 13 (S336) ◽  
pp. 397-398
Author(s):  
L. Uscanga ◽  
J. F. Gómez ◽  
J. A. Green ◽  
O. Suárez ◽  
H.-H. Qiao ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Radio Emission ◽  
Ground State ◽  
Planetary Nebulae ◽  
State Transitions ◽  
Preliminary Results ◽  
Shaping Process ◽  
The Magnetic Field ◽  
Compact Array

AbstractWe present polarimetric observations of the 4 ground-state transitions of OH, toward a sample of maser-emitting planetary nebulae (PNe) using the Australia Telescope Compact Array. This sample includes confirmed OH-emitting PNe, confirmed and candidate H2O-maser-emitting PNe. Polarimetric observations provide information related to the magnetic field of these sources. Maser-emitting PNe are very young PNe and magnetic fields are a key ingredient in the early evolution and shaping process of PNe. Our preliminary results suggest that magnetic field strengths may change very rapidly in young PNe.

scholarly journals A Method of Determination of the Temperature of Nuclei of the Planetary Nebulae

1968 ◽  
Vol 34 ◽  
pp. 330-331
Author(s):  
G.S. Khromov
Keyword(s):  
Heavy Ions ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Independent Method ◽  
Heavy Elements ◽  
Color Temperature ◽  
High Excitation ◽  
Method Of Determination

I would like to make a few comments on the problem of the determination of the temperatures of nuclei of planetary nebulae.It can be shown that in a high-excitation planetary nebula two independent Strömgren zones of heavy elements can be found. The first is a He III zone; the second corresponds to a zone of the luminescence of Ne V forbidden lines and originates due to combined absorption by the heavy ions Ne IV, O V and N V. If so, a relatively independent method of the determination of the color temperature of nuclei can be suggested.

scholarly journals High-resolution spectroscopic study of the planetary nebula Abell 78

1999 ◽  
Vol 193 ◽  
pp. 374-375
Author(s):  
Selene Medina ◽  
Miriam Peña
Keyword(s):  
Chemical Composition ◽  
High Resolution ◽  
Spectroscopic Study ◽  
Spectral Resolution ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Central Star ◽  
Heavy Elements ◽  
Physical Parameters ◽  
Processed Material

High resolution optical spectra of the planetary nebula Abell 78 were gathered, covering the wavelength ranges 3500–6600 Å and 3358–7361 Å, with a spectral resolution of ∼0.1 Å. Two different regions of Abell 78 are analyzed: the strongest knot near the central star which is thought to be a mass-loaded wind from the central star, and the outer, hydrogen-rich envelope. Physical parameters and chemical composition of both regions are estimated. The inner knot appears to be cooler and denser than the hydrogen-rich envelope. The chemical composition of the inner knot shows that there is almost no hydrogen near the central star and the emission is dominated by helium and processed material which has been dredged-up from the inner layers of the star. The outer, hydrogen-rich envelope appears to be deficient in heavy elements, mainly in oxygen, compared to the average abundances that are found among galactic planetary nebulae.

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