scholarly journals Abundances in Cool Evolved Stars

1988 ◽  
Vol 108 ◽  
pp. 17-30
Author(s):  
Catherine A. Pilachowski
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Chemical Compositions ◽  
Helium Burning ◽  
The Core ◽  
Evolved Stars ◽  
Peculiar Stars

Nature has filled the upper right quadrant of the Hertzsprung-Russell diagram with more varieties of peculiar stars and odd chemical compositions than even our most speculative observers and theorists could dream up. To bring some structure to this vast subject I will categorize the phenomena we observe according to our model of stellar evolution, dividing the stars among the first ascent of the giant branch and the core-helium burning phase, the asymptotic giant branch (double shell-burning) phase, and the post-AGB and pre-planetary nebula stars. The types of stars found in these three groups are summarized below.

scholarly journals The Clump Giants: A Spectroscopic Survey of G and K Giants in Open Clusters

1978 ◽  
Vol 80 ◽  
pp. 157-160
Author(s):  
Catherine A. Pilachowski ◽  
Walter K. Bonsack
Keyword(s):  
Stellar Evolution ◽  
Open Clusters ◽  
The Other ◽  
Similar Proportion ◽  
Helium Burning ◽  
The Core ◽  
Evolutionary State ◽  
Peculiar Stars ◽  
Absolute Magnitudes ◽  
Process Elements

The clump giants in old and middle-aged open clusters provide a sample of stars whose evolutionary state can be clearly identified as core helium burning (Cannon 1970). The evolutionary state of the Ba II stars, on the other hand, is at present undetermined. The enrichment of s-process elements in the atmospheres of these peculiar stars suggests that the stars have at least passed through double shell burning, where the heavy elements may be produced and mixed to the surface. The Ba II stars are, however, too faint to be associated with this phase of stellar evolution; the absolute magnitudes and temperatures are consistent with the core helium burning phase. The barium stars should then occur in the clumps of Population I clusters in similar proportion to their numbers among the field giants.

scholarly journals The spectra of evolved stars at 20–25 GHz: Tracing circumstellar chemistry during the asymptotic giant branch to planetary nebula transition

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Yong Zhang ◽  
Wayne Chau ◽  
Jun-ichi Nakashima ◽  
Sun Kwok
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Evolutionary Sequence ◽  
Frequency Range ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Line Survey ◽  
And Inversion

Abstract We report an unbiased radio line survey towards the circumstellar envelopes of evolved stars at the frequency range from 20 to 25 GHz, aiming to obtain a more complete unbiased picture of the chemical evolution in the final stages of stellar evolution. The observation sample includes the asymptotic giant branch (AGB) star IRC +10216, the proto-planetary nebulae (PPNs) CRL 2688 and CRL 618, and the young planetary nebula (PN) NGC 7027, representing an evolutionary sequence spanning about 10000 years. Rotational transitions from cyanopolyyne chains and inversion lines from ammonia are detected in the AGB star and PPNs, while the PN displays several recombination lines. The different spectral behaviors of these evolved stars clearly reflect the evolution of circumstellar chemistry during the AGB–PPN–PN transitions.

scholarly journals New models for the rapid evolution of the central star of the Stingray Nebula

2021 ◽  
Author(s):  
T M Lawlor
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Rapid Evolution ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Initial Mass ◽  
Thermal Pulse ◽  
The Past ◽  
New Models

Abstract We present stellar evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase for models of initial mass 1.2 M⊙ and 2.0 M⊙ that experience a Late Thermal Pulse (LTP), a helium shell flash that occurs following the AGB and causes a rapid looping evolution between the AGB and PN phase. We use these models to make comparisons to the central star of the Stingray Nebula, V839 Ara (SAO 244567). The central star has been observed to be rapidly evolving (heating) over the last 50 to 60 years and rapidly dimming over the past 20–30 years. It has been reported to belong to the youngest known planetary nebula, now rapidly fading in brightness. In this paper we show that the observed timescales, sudden dimming, and increasing Log(g), can all be explained by LTP models of a specific variety. We provide a possible explanation for the nebular ionization, the 1980’s sudden mass loss episode, the sudden decline in mass loss, and the nebular recombination and fading.

scholarly journals Rotation and Stellar Evolution

1981 ◽  
Vol 93 ◽  
pp. 237-256
Author(s):  
R. Kippenhahn ◽  
H.-C. Thomas
Keyword(s):  
Magnetic Field ◽  
Stellar Evolution ◽  
Chemical Elements ◽  
Line Broadening ◽  
General Magnetic Field ◽  
The Core ◽  
Evolved Stars

Does rotation influence stellar evolution? Does it cause observational effects other than line broadening? Can rotation be responsible for mixing of chemical elements throughout the star? Do evolved stars have rapidly rotating cores? This, for instance, is of interest if one wants to compute the details of supernova events. We are not sure whether rotation has really important effects on the life of a star. There might be no rapidly rotating cores. If we think that a fossile general magnetic field couples core and envelope of an evolved star, the core will always be slowed down by the big inertial momentum of the outer regions.

scholarly journals Mass-Losing AGB Stars in the Magellanic Clouds

1993 ◽  
Vol 155 ◽  
pp. 319-319
Author(s):  
Neill Reid
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Luminosity Function ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
The Future ◽  
Giant Branch Stars

Asymptotic giant branch stars are the immediate precursors to the planetary nebula stage of stellar evolution. It is clear that the latter stages of a stars life on the AGB are accompanied by either continuous or episodic mass-loss, with the final convulsion being the ejection of the envelope (the future planetary shell), the gradual exposure of the bare CO core and the rapid horizontal evolution to the blue in the H-R diagram. Thus, the structure of the planetary nebula luminosity function, particularly at the higher luminosities (although this phase is extremely rapid), is intimately tied to the luminosity function of the AGB.

scholarly journals Structure and Evolution of Planetary Nebula Haloes

2003 ◽  
Vol 209 ◽  
pp. 439-446 ◽  
Author(s):  
Matthias Steffen ◽  
Detlef Schönberner
Keyword(s):  
Mass Loss ◽  
Numerical Simulations ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Previous History ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Time Dependent ◽  
Density Structure ◽  
History Of

The density structure of the extended haloes of Planetary Nebulae (PN) is generally believed to reflect the previous history of heavy mass loss during the final stages of stellar evolution on the asymptotic giant-branch (AGB). In this review, we discuss different interpretations of the observed PN halo structures in the light of recent numerical simulations combining detailed AGB and post-AGB stellar evolution calculations with time-dependent hydrodynamical wind models.

scholarly journals The first water fountain in a planetary nebula

2012 ◽  
Vol 8 (S287) ◽  
pp. 230-234
Author(s):  
Olga Suárez ◽  
José Francisco Gómez ◽  
Philippe Bendjoya ◽  
Luis. F. Miranda ◽  
Martín. A. Guerrero ◽  
...  
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Survival Times ◽  
Jet Formation ◽  
Evolved Stars ◽  
Water Masers ◽  
First Time ◽  
Water Maser

AbstractWater fountains are evolved stars showing water masers with velocity spanning more than ~100 km/s. They usually appear at the end of the Asymptotic Giant Branch (AGB) phase or at the beginning of the post-AGB phase, and their masers trace the first manifestation of axisymmetric collimated mass-loss. For the first time, masers with water fountain characteristics have been detected towards a PN (IRAS 15103–5754), which might require a revision of the current theories about jet formation and survival times. IRAS 15103-5754 was observed using the ATCA interferometer at 22 GHz (both continuum and water maser). The main results of these observations are summarized here. The evolutionary classification of this object is also discussed.

scholarly journals Hydrogen and Helium Burning Evolutionary Tracks

1993 ◽  
Vol 155 ◽  
pp. 465-468
Author(s):  
P.R. Wood ◽  
E. Vassiliadis
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Luminosity Function ◽  
Helium Burning

We discuss the effect of metallicity on the luminosities of planetary nebula nuclei (PNNi), and we use theoretical stellar evolution calculations to predict the fraction of PNNi that enter the planetary nebula domain burning helium rather than hydrogen. Both these factors will clearly influence the planetary nebula luminosity function.

scholarly journals Proto-Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 113-120 ◽  
Author(s):  
Bruce J. Hrivnak
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Central Stars

The study of proto-planetary nebulae (PPNs) leads to a better understanding of both the preceding asymptotic giant branch and the succeeding planetary nebula phases of stellar evolution. Recent results are reviewed, emphasizing the properties of the central stars and the shape and chemistry of the nebulae. The study of PPNs is seen to be important in its own right.

scholarly journals Open Clusters and Stellar Evolution

1980 ◽  
Vol 85 ◽  
pp. 195-214
Author(s):  
Gretchen L.H. Harris
Keyword(s):  
Stellar Evolution ◽  
Initial Conditions ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Potential Importance ◽  
Helium Burning ◽  
The Core ◽  
Magnitude Diagram

Several topics relevant to the study of stellar evolution through open clusters are discussed. These include composite color-magnitude diagrams, the need for thorough studies of populous clusters, parameters affecting the core helium burning stage, and the potential importance of initial conditions and dynamical evolution on the cluster color-magnitude diagram.

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