Stellar Evolution, Mass Loss and Nucleosynthesis on the Asymptotic Giant Branch

1981 ◽  
Vol 4 (2) ◽  
pp. 145-148
Author(s):  
P. R. Wood
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Horizontal Branch ◽  
Helium Burning ◽  
Red Giant ◽  
Hr Diagram

In this review, I will be concentrating on problems related to the evolution of stars on the asymptotic giant branch (AGB). AGB stars are defined as stars which have completed core helium burning and have subsequently developed degenerate carbon/oxygen cores surrounded by hydrogen and helium burning shells; such stars have main sequence masses M≤9 M⊙ (Paczynski 1971; Becker and Iben 1980). In the HR diagram most AGB stars sit on the red giant branch. An exception to this rule occurs in Population II systems, where the AGB stars evolve asymptotically to the red giant branch from the blue side as the luminosity increases after completion of core helium burning on the horizontal branch.

scholarly journals White Dwarfs

1994 ◽  
Vol 146 ◽  
pp. 71-78
Author(s):  
Peter Thejll
Keyword(s):  
Mass Loss ◽  
White Dwarfs ◽  
Main Sequence ◽  
Asymptotic Giant Branch ◽  
List Type ◽  
Stellar Core ◽  
The Core ◽  
Long Time ◽  
Red Giant ◽  
Carbon Burning

It is the intention of this review to explain what white dwarfs are and why it is interesting to study them, and why the H+2molecule is of special interest.The evolution, from start to finish, of a star of mass less than about 2 solar masses (M⊙), can roughly be summarized as follows:–A cloud of gas contracts from the interstellar medium until hydrogen ignites at the center and amain sequence(MS) star forms. H is transformed to He and the MS phase continues until H is exhausted in the stellar core.–H continues burning in a shell outside the He core while the core contracts. He “ashes” are added to the core, and ared giantstar is formed as the envelope expands. The star evolves up the Red Giant Branch (RGB) (i.e. it becomes more and more luminous and the surface cools).–Towards the end of the RGB phase, mass-loss from the upper layers increases until helium to carbon burning in the core ignites suddenly under degenerate conditions – this is called theHelium Flash(HF). The HF terminates the RGB evolution, and therefore also the mass-loss and the growth of the stellar core.–The star readjusts its structure and the He-core burns steadily on thehorizontal branch(HB) (a phase of nearly-constant luminosity) until fuel is exhausted in the He-core.–Then the C/O core contracts anew and the expansion of the envelope, and the growth of the core, during He-shell burning, mimics RGB evolution but relatively little mass is added to the core this time.–The second ascent of the giant branch (the so-called Asymptotic Giant Branch, or AGB) continues with increased mass loss towards the end–Rapid detachment of a considerable fraction of the remaining envelope and the hot core takes place, sometimes observable as thePlanetary Nebulae(PN) phase.–The PN is dispersed as the core contracts to a white dwarf (WD).–The WD cools for a long time, as internal kinetic energy and latent heat is released.

scholarly journals TP-AGB stars in population synthesis models

2009 ◽  
Vol 5 (S262) ◽  
pp. 36-43 ◽  
Author(s):  
Paola Marigo ◽  
Léo Girardi ◽  
Alessandro Bressan ◽  
Bernhard Aringer ◽  
Marco Gullieuszik ◽  
...  
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Population Synthesis ◽  
Future Developments ◽  
First Results ◽  
Nearby Galaxies ◽  
The Subject

AbstractIn spite of its relevance, the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase is one of the most uncertain phases of stellar evolution, and a major source of disagreement between the results of different population synthesis models of galaxies. I will briefly review the existing literature on the subject, and recall the basic prescriptions that have been used to fix the contribution of TP-AGB stars to the integrated light of stellar populations. The simplicity of these prescriptions greatly contrasts with the richness of details provided by present-day databases of AGB stars in the Magellanic Clouds, which are now being extended to other nearby galaxies. I will present the first results of an ongoing study aimed at simulating photometry, chemistry, pulsation, mass loss, dust properties of AGB star populations in resolved and un-resolved galaxies. We test our predictions against observations from various surveys of the Magellanic Clouds (DENIS, 2MASS, OGLE, MACHO, Spitzer, and AKARI). I will discuss the implications and outline the plan of future developments.

scholarly journals Wind morphology around cool evolved stars in binaries

2020 ◽  
Vol 637 ◽  
pp. A91 ◽  
Author(s):  
I. El Mellah ◽  
J. Bolte ◽  
L. Decin ◽  
W. Homan ◽  
R. Keppens
Keyword(s):  
Mass Loss ◽  
Adaptive Mesh Refinement ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Large Fraction ◽  
Orbital Plane ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Evolved Stars

Context. The late evolutionary phase of low- and intermediate-mass stars is strongly constrained by their mass-loss rate, which is orders of magnitude higher than during the main sequence. The wind surrounding these cool expanded stars frequently shows nonspherical symmetry, which is thought to be due to an unseen companion orbiting the donor star. The imprints left in the outflow carry information about the companion and also the launching mechanism of these dust-driven winds. Aims. We study the morphology of the circumbinary envelope and identify the conditions of formation of a wind-captured disk around the companion. Long-term orbital changes induced by mass loss and mass transfer to the secondary are also investigated. We pay particular attention to oxygen-rich, that is slowly accelerating, outflows in order to look for systematic differences between the dynamics of the wind around carbon and oxygen-rich asymptotic giant branch (AGB) stars. Methods. We present a model based on a parametrized wind acceleration and a reduced number of dimensionless parameters to connect the wind morphology to the properties of the underlying binary system. Thanks to the high performance code MPI-AMRVAC, we ran an extensive set of 72 three-dimensional hydrodynamics simulations of a progressively accelerating wind propagating in the Roche potential of a mass-losing evolved star in orbit with a main sequence companion. The highly adaptive mesh refinement that we used, enabled us to resolve the flow structure both in the immediate vicinity of the secondary, where bow shocks, outflows, and wind-captured disks form, and up to 40 orbital separations, where spiral arms, arcs, and equatorial density enhancements develop. Results. When the companion is deeply engulfed in the wind, the lower terminal wind speeds and more progressive wind acceleration around oxygen-rich AGB stars make them more prone than carbon-rich AGB stars to display more disturbed outflows, a disk-like structure around the companion, and a wind concentrated in the orbital plane. In these configurations, a large fraction of the wind is captured by the companion, which leads to a significant shrinking of the orbit over the mass-loss timescale, if the donor star is at least a few times more massive than its companion. In the other cases, an increase of the orbital separation is to be expected, though at a rate lower than the mass-loss rate of the donor star. Provided the companion has a mass of at least a tenth of the mass of the donor star, it can compress the wind in the orbital plane up to large distances. Conclusions. The grid of models that we computed covers a wide scope of configurations: We vary the terminal wind speed relative to the orbital speed, the extension of the dust condensation region around the cool evolved star relative to the orbital separation, and the mass ratio, and we consider a carbon-rich and an oxygen-rich donor star. It provides a convenient frame of reference to interpret high-resolution maps of the outflows surrounding cool evolved stars.

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 Parameterizing the Third Dredge up in AGB Stars

2003 ◽  
Vol 209 ◽  
pp. 82-82 ◽  
Author(s):  
A. I. Karakas ◽  
J. C. Lattanzio ◽  
O. R. Pols
Keyword(s):  
Mass Loss ◽  
Main Sequence ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Intermediate Mass ◽  
The Third ◽  
Intermediate Mass Stars

We present new evolutionary sequences for low and intermediate mass stars (1M⊙ to 6M⊙) for three different metallicities, z = 0.02, 0.008 and 0.004. We evolve the models from the pre-main sequence to the thermally-pulsing asymptotic giant branch (AGB) phase. We have two sequences of models for each mass, one which includes mass-loss and one without mass-loss. For an overview of AGB evolution and nucleosynthesis, see Herwig (2002) and Lattanzio (2002).

scholarly journals A Preliminary Investigation of Period Changes For W Virginis Stars in Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 145-149
Author(s):  
Christine M. Coutts
Keyword(s):  
Globular Clusters ◽  
Preliminary Investigation ◽  
Instability Region ◽  
Horizontal Branch ◽  
Helium Burning ◽  
Red Giant ◽  
Branch Star ◽  
Hr Diagram

Investigations in recent years have shown that there may be two mechanisms which place stars in the W Virginis instability region (Kraft, 1972). The variables with periods less than 8 days seem to be in the stage of ‘above horizontal branch’ evolution discussed by Strom et al. (1970). The longer period group apparently results when thermal instabilities in the helium burning shell of an asymptotic red giant branch star cause it to loop to the left in the HR diagram. This longer period group has been investigated by Schwarzschild and Härm (1970) and Mengel (1972). The present study has been undertaken to see if there are any notable differences between the period changes of variables belonging to the two groups.

scholarly journals Observational evidence of third dredge-up occurrence in S-type stars with initial masses around 1 M⊙

2019 ◽  
Vol 625 ◽  
pp. L1 ◽  
Author(s):  
S. Shetye ◽  
S. Goriely ◽  
L. Siess ◽  
S. Van Eck ◽  
A. Jorissen ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Reasonable Agreement ◽  
Direct Evidence ◽  
Observational Evidence ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Data Release ◽  
Low Mass ◽  
M Stars ◽  
Hr Diagram

Context. S stars are late-type giants with spectra showing characteristic molecular bands of ZrO in addition to the TiO bands typical of M stars. Their overabundance pattern shows the signature of s-process nucleosynthesis. Intrinsic, technetium (Tc)-rich S stars are the first objects on the asymptotic giant branch (AGB) to undergo third dredge-up (TDU) events. Exquisite Gaia parallaxes now allow for these stars to be precisely located in the Hertzsprung–Russell (HR) diagram. Here we report on a population of low-mass, Tc-rich S stars previously unaccounted for by stellar evolution models. Aims. Our aim is to derive parameters for a sample of low-mass, Tc-rich S stars and then, by comparing their location in the HR diagram with stellar evolution tracks, to derive their masses and to compare their measured s-process abundance profiles with recently derived STAREVOL nucleosynthetic predictions for low-mass AGB stars. Methods. Stellar parameters were obtained using a combination of HERMES high-resolution spectra, accurate Gaia Data Release 2 (Gaia-DR2) parallaxes, stellar-evolution models, and newly designed MARCS model atmospheres for S-type stars. Results. We report on six Tc-rich S stars lying close to the 1 M⊙ (initial mass) tracks of AGB stars of the corresponding metallicity and above the predicted onset of TDU, as expected. This provides direct evidence for TDUs occurring in AGB stars with initial masses as low as ∼1 M⊙ and at low luminosity, that is, at the start of the thermally pulsing AGB. We present AGB models producing TDU in those stars with [Fe/H] in the range −0.25 to −0.5. There is reasonable agreement between the measured and predicted s-process abundance profiles. For two objects however, CD −29°5912 and BD +34°1698, the predicted C/O ratio and s-process enhancements do not simultaneously match the measured ones.

scholarly journals On the role of reduced wind mass-loss rate in enabling exoplanets to shape planetary nebulae

2020 ◽  
Vol 496 (1) ◽  
pp. 612-619
Author(s):  
Ahlam Hegazi ◽  
Ealeal Bear ◽  
Noam Soker
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Semimajor Axis ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Early Conclusion ◽  
Future Evolution ◽  
Red Giant ◽  
Parent Star

ABSTRACT We use the stellar evolution code MESA–binary and follow the evolution of three exoplanets and two brown dwarfs (BDs) to determine their potential role in the future evolution of their parent star on the red giant branch (RGB) and on the asymptotic giant branch (AGB). We limit this study to exoplanets and BDs with orbits that have semimajor axis of $1 {~\rm au}\lesssim a_0 \lesssim 20 {~\rm au}$, a high eccentricity, $e_0 \gtrsim 0.25$, and having a parent star of mass M*,0 ≥ 1 M⊙. We find that the star HIP 75 458 will engulf its planet HIP 75 458b during its RGB phase. The planet will remove the envelope and terminate the RGB evolution, leaving a bare helium core of mass 0.4 M⊙ that will evolve to form a helium white dwarf. Only in one system out of five, the planet beta Pic c will enter the envelope of its parent star during the AGB phase. For that to occur, we have to reduce the wind mass-loss rate by a factor of about four from its commonly used value. This strengthens an early conclusion, which was based on exoplanets with circular orbits, which states that to have a non-negligible fraction of AGB stars that engulf planets we should consider lower wind mass-loss rates of isolated AGB stars (before they are spun-up by a companion). Such an engulfed planet might lead to the shaping of the AGB mass-loss geometry to form an elliptical planetary nebula.

scholarly journals Revealing infrared populations of nearby galaxies using the Spitzer Space Telescope

2009 ◽  
Vol 5 (S262) ◽  
pp. 111-114
Author(s):  
Mikako Matsuura
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Asymptotic Giant Branch ◽  
Evolutionary Stage ◽  
Agb Stars ◽  
Spitzer Space Telescope ◽  
Space Telescope ◽  
Chemical Enrichment ◽  
Nearby Galaxies ◽  
Enrichment Process

AbstractDue to their brightness in infrared, asymptotic giant branch (AGB) stars are in important evolutionary stage to be understood at this wavelength. In particular, in next decades, when the infrared optimised telescopes, such as the JWST and the ELT are in operation, it will be essential to include the AGB phase more precisely into the population synthesis models. However, the AGB phase is still one of the remaining major problems in the stellar evolution. This is because the AGB stellar evolution is strongly affected by the mass-loss process from the stars. It is important to describe mass loss more accurately so as to incorporate it into stellar evolutionary models. Recent observations using the Spitzer Space Telescope (SST) enabled us to make a significant progress in understanding the mass loss from AGB stars. Moreover, the SST large surveys contributed to our understanding of the role of AGB stars in chemical enrichment process in galaxies. Here we present the summary of our recent progress.

scholarly journals Fast and Automated Peak Bagging with DIAMONDS (FAMED)

2020 ◽  
Vol 640 ◽  
pp. A130
Author(s):  
E. Corsaro ◽  
J. M. McKeever ◽  
J. S. Kuszlewicz
Keyword(s):  
Main Sequence ◽  
Oscillation Mode ◽  
Asymptotic Giant Branch ◽  
Helium Burning ◽  
Mode Identification ◽  
Wide Range ◽  
Oscillation Modes ◽  
Red Giant ◽  
Stellar Properties ◽  
Subgiant Stars

Stars of low and intermediate mass that exhibit oscillations may show tens of detectable oscillation modes each. Oscillation modes are a powerful tool to constrain the internal structure and rotational dynamics of the star, hence allowing one to obtain an accurate stellar age. The tens of thousands of solar-like oscillators that have been discovered thus far are representative of the large diversity of fundamental stellar properties and evolutionary stages available. Because of the wide range of oscillation features that can be recognized in such stars, it is particularly challenging to properly characterize the oscillation modes in detail, especially in light of large stellar samples. Overcoming this issue requires an automated approach, which has to be fast, reliable, and flexible at the same time. In addition, this approach should not only be capable of extracting the oscillation mode properties of frequency, linewidth, and amplitude from stars in different evolutionary stages, but also able to assign a correct mode identification for each of the modes extracted. Here we present the new freely available pipeline FAMED (Fast and AutoMated pEak bagging with DIAMONDS), which is capable of performing an automated and detailed asteroseismic analysis in stars ranging from the main sequence up to the core-helium-burning phase of stellar evolution. This, therefore, includes subgiant stars, stars evolving along the red giant branch (RGB), and stars likely evolving toward the early asymptotic giant branch. In this paper, we additionally show how FAMED can detect rotation from dipolar oscillation modes in main sequence, subgiant, low-luminosity RGB, and core-helium-burning stars.

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