scholarly journals Magnetic fields during the evolution towards planetary nebulae

2011 ◽  
Vol 7 (S283) ◽  
pp. 176-179 ◽  
Author(s):  
Wouter Vlemmings
Keyword(s):  
Magnetic Fields ◽  
Energy Budget ◽  
Magnetic Energy ◽  
Planetary Nebulae ◽  
Central Star ◽  
Agb Stars ◽  
Evolved Stars ◽  
Short Summary ◽  
New Instruments

AbstractMagnetic fields appear ubiquitous throughout the envelopes of evolved stars. However, their origin and role in the formation of planetary nebulae is still unclear. As observations of magnetic fields are complicated and time consuming, the observed samples of AGB and post-AGB stars and planetary nebulae are still small. Still, magnetic energy seems to dominate the energy budget out to a distance of several tens of AU from the central star and the field morphology often appears to be well ordered. A short summary is given of the current observations and the potential of new instruments such as ALMA is discussed.

scholarly journals Chemical Enrichment and Central Star Properties

1993 ◽  
Vol 155 ◽  
pp. 572-572
Author(s):  
C.Y. Zhang
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Agb Stars ◽  
Physical Processes ◽  
Chemical Abundances ◽  
Core Mass ◽  
Chemical Enrichment ◽  
The Core ◽  
Stellar Temperature ◽  
Independent Parameters

We have selected a sample of planetary nebulae, for which the core masses are determined using distance-independent parameters (Zhang and Kwok 1992). The chemical abundances of He, N, O, and C are taken from the literature for them. Relationships of the ratios of He/H, N/O, and C/O with various stellar parameters of planetary nebulae (PN), such as the core mass, the mass of the core plus the ionized nebular gas, the stellar age and temperature, are examined. It is found that the N/O increases with increasing mass, while the C/O first increases and then decreases with the core mass. No strong correlation seems to exist between the He/H and the core mass. A correlation of the N/O and He/H with the stellar temperature exists. The current dredge-up theory for the progenitor AGB stars cannot satisfactorily account for these patterns of chemical enrichment in PN. Furthermore, the correlations of the N/O and He/H with the stellar age and temperature indicate that besides the dredge-ups in the RG and AGB stages, physical processes that happen in the planetary nebula stage may also play a role in forming the observed patterns of chemical enrichment in the planetary nebulae.

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.

The real time evolution of post-AGB stars

2019 ◽  
Vol 15 (S357) ◽  
pp. 154-157
Author(s):  
Marcin Hajduk
Keyword(s):  
Real Time ◽  
Time Evolution ◽  
Planetary Nebulae ◽  
Theoretical Models ◽  
Central Star ◽  
Maximum Temperature ◽  
Additional Parameter ◽  
Agb Stars ◽  
The Real ◽  
Hr Diagram

AbstractEvolution of post-AGB stars is extremely fast. They cross the HR diagram vertically on a timescale of hundreds to some ten thousands of years to reach maximum temperature in their lifetime. This is reflected in an increasing excitation of planetary nebulae on a timescale of years and decades. Since evolutionary timescale of post-AGB stars is very sensitive to their mass, observed changes can be used to determine model dependent central star masses. If an additional parameter is determined (e.g. luminosity or dynamic age), the observed evolution of planetary nebulae can be utilized for observational verification of theoretical models.

scholarly journals Rings and arcs around evolved stars – II. The Carbon Star AFGL 3068 and the Planetary Nebulae NGC 6543, NGC 7009, and NGC 7027

2020 ◽  
Vol 495 (2) ◽  
pp. 2234-2246 ◽  
Author(s):  
M A Guerrero ◽  
G Ramos-Larios ◽  
J A Toalá ◽  
B Balick ◽  
L Sabin
Keyword(s):  
Proper Motion ◽  
Planetary Nebulae ◽  
Carbon Star ◽  
Agb Stars ◽  
Spiral Pattern ◽  
High Quality ◽  
Hydrodynamic Simulations ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Regular Patterns

ABSTRACT We present a detailed comparative study of the arcs and fragmented ring-like features in the haloes of the planetary nebulae (PNe) NGC 6543, NGC 7009, and NGC 7027 and the spiral pattern around the carbon star AFGL 3068 using high-quality multi-epoch HST images. This comparison allows us to investigate the connection and possible evolution between the regular patterns surrounding AGB stars and the irregular concentric patterns around PNe. The radial proper motion of these features, ≃15 km s−1, are found to be consistent with the AGB wind and their linear sizes and interlapse times (500–1900 yr) also agree with those found around AGB stars, suggesting a common origin. We find evidence using radiative-hydrodynamic simulations that regular patterns produced at the end of the AGB phase become highly distorted by their interactions with the expanding PN and the anisotropic illumination and ionization patterns caused by shadow instabilities. These processes will disrupt the regular (mostly spiral) patterns around AGB stars, plausibly becoming the arcs and fragmented rings observed in the haloes of PNe.

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 Stellar yields and abundances: new directions from planetary nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 86-94
Author(s):  
Maria Lugaro ◽  
Amanda I. Karakas ◽  
Marco Pignatari ◽  
Carolyn L. Doherty
Keyword(s):  
Noble Gas ◽  
Planetary Nebulae ◽  
Central Star ◽  
High Energy ◽  
Type I ◽  
Agb Stars ◽  
Capture Process ◽  
New Directions ◽  
Energy Environment ◽  
Central Stars

AbstractPlanetary nebulae retain the signature of the nucleosynthesis and mixing events that occurred during the previous AGB phase. Observational signatures complement observations of AGB and post-AGB stars and their binary companions. The abundances of the elements heavier than iron such as Kr and Xe in planetary nebulae can be used to complement abundances of Sr/Y/Zr and Ba/La/Ce in AGB stars, respectively, to determine the operation of theslowneutron-capture process (thesprocess) in AGB stars. Additionally, observations of the Rb abundance in Type I planetary nebulae may allow us to infer the initial mass of the central star. Several noble gas components present in meteoritic stardust silicon carbide (SiC) grains are associated with implantation into the dust grains in the high-energy environment connected to the fast winds from the central stars during the planetary nebulae phase.

scholarly journals ISO's View of the Molecular Content of Evolved Stars

2000 ◽  
Vol 197 ◽  
pp. 375-390
Author(s):  
J. Cernicharo
Keyword(s):  
Systematic Study ◽  
Molecular Species ◽  
Planetary Nebulae ◽  
Far Infrared ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Mid Infrared ◽  
Evolved Stars ◽  
Vibrational Bands

The recent results of the ISO satellite in the field of molecular spectrocopy of AGB stars are reviewed. For the fist time, the two spectrometers onboard ISO have provided the opportunity to observe the pure rotational lines of several molecules in the far infrared and the ro-vibrational bands of the most abundant molecular species in the near and mid-infrared. These data allow to carry out a systematic study of the circumstellar envelopes of AGB stars and Planetary Nebulae. I analyze in this paper the role of resonant scatterring in the pumping of the ro-vibrational molecular levels in CSEs.

scholarly journals Polyynes and Polycyclic Aromatic Molecules in C-rich Circumstellar Envelopes

1994 ◽  
Vol 146 ◽  
pp. 134-148 ◽  
Author(s):  
Alain Omont
Keyword(s):  
Planetary Nebulae ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Aromatic Molecules ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Polycyclic Aromatic ◽  
Circumstellar Shells ◽  
Evolution Stage ◽  
Circumstellar Environment

The aim of this review is to discuss our knowledge on molecules in the circumstellar environment of evolved stars. In particular the presence and the behaviour of various kinds of molecules with several or many carbon atoms, in relation to C-rich dust, is considered.Such objects include mainly: (i) circumstellar shells of AGB carbon stars, either visible (such as Y CVn) or infrared (such as IRC+10216 (CW Leo)); (ii) planetary nebulae (PNe, e.g. NGC 7027); (iii) pre-planetary nebulae (PPNe, also called post-AGB stars, such as CRL 2688 or the Red Rectangle), probably in an intermediate evolution stage between the two former classes. I will not discuss more peculiar classes, such as R CrB stars and novae, for which very little is known about the presence of such molecular species.

scholarly journals Is there a Connection Between Thermal Pulses and PNe Halos: An Approach to an Answer

1993 ◽  
Vol 155 ◽  
pp. 365-365
Author(s):  
Adam Frank ◽  
Bruce Balick ◽  
Will Van Der Veen
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Published Data ◽  
Agb Stars ◽  
Thermal Pulses

We wish to explore the hypothesis that the shells and halos of planetary nebulae are formed during the thermal pulsing of progenitor AGB stars. Using published data and model results we compare the AGB interpulse time ΔtT and the time between shell ejections ΔtD for a sample of PNe with halos. ΔtT is derived from the Paczynski relation using the PNe central star luminosity. ΔtD is calculated using the radii and velocity of PNe shells and halos.

scholarly journals Planetary Nebula Evolution Traced by Distance-Independent Parameters

1993 ◽  
Vol 155 ◽  
pp. 480-480
Author(s):  
C.Y. Zhang ◽  
S. Kwok
Keyword(s):  
Physical Properties ◽  
Mass Distribution ◽  
Planetary Nebula ◽  
Strong Support ◽  
Planetary Nebulae ◽  
Central Star ◽  
Evolution Model ◽  
The Core ◽  
Independent Parameters ◽  
Central Stars

Making use of the results from recent infrared and radio surveys of planetary nebulae, we have selected 431 nebulae to form a sample where a number of distance-independent parameters (e.g., Tb, Td, I60μm and IRE) can be constructed. In addition, we also made use of other distance-independent parameters ne and T∗ where recent measurements are available. We have investigated the relationships among these parameters in the context of a coupled evolution model of the nebula and the central star. We find that most of the observed data in fact lie within the area covered by the model tracks, therefore lending strong support to the correctness of the model. Most interestingly, we find that the evolutionary tracks for nebulae with central stars of different core masses can be separated in a Tb-T∗ plane. This implies that the core masses and ages of the central stars can be determined completely independent of distance assumptions. The core masses and ages have been obtained for 302 central stars with previously determined central-star temperatures. We find that the mass distribution of the central stars strongly peaks at 0.6 M⊙, with 66% of the sample having masses <0.64 MM⊙. The luminosities of the central stars are then derived from their positions in the HR diagram according to their core masses and central star temperatures. If this method of mass (and luminosity) determination turns out to be accurate, we can bypass the extremely unreliable estimates for distances, and will be able to derive other physical properties of planetary nebulae.

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