scholarly journals Stellar yields – theory and observations

2015 ◽  
Vol 11 (A29B) ◽  
pp. 162-163
Author(s):  
Amanda I. Karakas
Keyword(s):  
Chemical Evolution ◽  
Stellar Evolution ◽  
Theoretical Calculations ◽  
Theoretical Models ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Chemically Peculiar ◽  
Essential Tool

AbstractStellar yields are an essential tool for studies of chemical evolution. For low and intermediate-mass stars (0.8 up to 8-10M⊙) the richest nucleosynthesis occurs when the stars are on the asymptotic giant branch (AGB) of stellar evolution. We discuss the main nucleosynthesis outcomes, along with the uncertainties that affect the theoretical calculations. The uncertainties in the physics can be improved by comparing theoretical models to observations, including chemically peculiar metal-poor stars, along with AGB stars and their progeny.

scholarly journals Monash Chemical Yields Project (Monχey) Element production in low- and intermediate-mass stars

2015 ◽  
Vol 11 (A29B) ◽  
pp. 164-165
Author(s):  
Carolyn Doherty ◽  
John Lattanzio ◽  
George Angelou ◽  
Simon W. Campbell ◽  
Ross Church ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Heavy Element ◽  
Internal Surface ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Galactic Chemical Evolution ◽  
Intermediate Mass ◽  
Mixing Processes ◽  
Intermediate Mass Stars ◽  
Solar Metallicity

AbstractThe Monχey project will provide a large and homogeneous set of stellar yields for the low- and intermediate- mass stars and has applications particularly to galactic chemical evolution modelling. We describe our detailed grid of stellar evolutionary models and corresponding nucleosynthetic yields for stars of initial mass 0.8 M⊙ up to the limit for core collapse supernova (CC-SN) ≈ 10 M⊙. Our study covers a broad range of metallicities, ranging from the first, primordial stars (Z = 0) to those of super-solar metallicity (Z = 0.04). The models are evolved from the zero-age main-sequence until the end of the asymptotic giant branch (AGB) and the nucleosynthesis calculations include all elements from H to Bi. A major innovation of our work is the first complete grid of heavy element nucleosynthetic predictions for primordial AGB stars as well as the inclusion of extra-mixing processes (in this case thermohaline) during the red giant branch. We provide a broad overview of our results with implications for galactic chemical evolution as well as highlight interesting results such as heavy element production in dredge-out events of super-AGB stars. We briefly introduce our forthcoming web-based database which provides the evolutionary tracks, structural properties, internal/surface nucleosynthetic compositions and stellar yields. Our web interface includes user- driven plotting capabilities with output available in a range of formats. Our nucleosynthetic results will be available for further use in post processing calculations for dust production yields.

scholarly journals Constraining ν-process production of fluorine through cosmic ray nucleosynthesis

2019 ◽  
Vol 490 (3) ◽  
pp. 4307-4316 ◽  
Author(s):  
Keith A Olive ◽  
Elisabeth Vangioni
Keyword(s):  
Stellar Evolution ◽  
Massive Star ◽  
Cosmic Ray ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Star Production ◽  
Low Metallicity ◽  
Galactic Cosmic Ray

ABSTRACT Fluorine is massive enough that it is not considered to be a light (Z ≤ 5) element, yet compared to its near neighbours, C, N, O, and Ne, it is far underproduced in the course of stellar evolution, making its origin more complex. In fact, the abundance of fluorine is the lowest among all elements between Z = 5 and 21 and is roughly 3–4 orders of magnitude below that of C, N, O, and Ne. There are several plausible sources for F beyond standard stellar evolution. These include the production in the asymptotic giant branch phase (AGB) in intermediate-mass stars, production in Wolf–Rayet stars, and the production through neutrino spallation in supernovae. The latter, known as the ν-process, is an important source for 11B, and may contribute to the abundance of 7Li as well. We combine a simple model of Galactic chemical evolution with a standard Galactic cosmic ray nucleosynthesis model to treat self-consistently the evolution of the Li, Be, and B isotopes. We include massive star production of F, as well as contributions from AGB stars, and the ν-process. Given the uncertainties in neutrino energies in supernovae, we normalize the ν-process using the observed 11B/10B ratio as a constraint. As a consequence, we are able to determine the relative importance of each contribution to the F abundance. We find that although the ν-process dominates at early times (low metallicity), the present-day F abundance is found to originate primarily from AGB stars.

scholarly journals The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars

2014 ◽  
Vol 31 ◽  
Author(s):  
Amanda I. Karakas ◽  
John C. Lattanzio
Keyword(s):  
Chemical Evolution ◽  
Surface Composition ◽  
Theoretical Calculations ◽  
Slow Neutron ◽  
Asymptotic Giant Branch ◽  
Intermediate Mass ◽  
Capture Process ◽  
Intermediate Mass Stars ◽  
Low Metallicity ◽  
The Universe

AbstractThe chemical evolution of the Universe is governed by the chemical yields from stars, which in turn are determined primarily by the initial stellar mass. Even stars as low as 0.9 M⊙can, at low metallicity, contribute to the chemical evolution of elements. Stars less massive than about 10 M⊙experience recurrent mixing events that can significantly change the surface composition of the envelope, with observed enrichments in carbon, nitrogen, fluorine, and heavy elements synthesized by the slow neutron capture process (thes-process). Low- and intermediate-mass stars release their nucleosynthesis products through stellar outflows or winds, in contrast to massive stars that explode as core-collapse supernovae. Here we review the stellar evolution and nucleosynthesis for single stars up to ~ 10 M⊙from the main sequence through to the tip of the asymptotic giant branch (AGB). We include a discussion of the main uncertainties that affect theoretical calculations and review the latest observational data, which are used to constrain uncertain details of the stellar models. We finish with a review of the stellar yields available for stars less massive than about 10 M⊙and discuss efforts by various groups to address these issues and provide homogeneous yields for low- and intermediate-mass stars covering a broad range of metallicities.

scholarly journals Evolutionary timescales from the AGB to the CSPNe phase

2018 ◽  
Vol 14 (S343) ◽  
pp. 36-46
Author(s):  
Marcelo M. Miller Bertolami
Keyword(s):  
White Dwarf ◽  
New Physics ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars

AbstractThe transition from the asymptotic giant branch (AGB) to the final white dwarf (WD) stage is arguably the least understood phase in the evolution of single low- and intermediate-mass stars (0.8 ≲ MZAMS/M⊙ ≲ 8…10). Here we briefly review the progress in the last 50 years of the modeling of stars during the post-AGB phase. We show that although the main features, like the extreme mass dependency of post-AGB timescales were already present in the earliest post-AGB models, the quantitative values of the computed post-AGB timescales changed every time new physics was included in the modeling of post-AGB stars and their progenitors. Then we discuss the predictions and uncertainties of the latest available models regarding the evolutionary timescales of post-AGB stars.

Nucleosynthesis in stars: The Origin of the Heaviest Elements

2018 ◽  
Vol 14 (S343) ◽  
pp. 79-88 ◽  
Author(s):  
Amanda I. Karakas
Keyword(s):  
Chemical Evolution ◽  
Neutron Capture ◽  
Recent Progress ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Capture Process ◽  
Intermediate Mass Stars ◽  
Intermediate Neutron ◽  
Heaviest Elements ◽  
The Universe

AbstractThe chemical evolution of the Universe is governed by the nucleosynthesis contribution from stars, which in turn is determined primarily by the initial stellar mass. The heaviest elements are primarily produced through neutron capture nucleosynthesis. Two main neutron capture processes identified are the slow and rapid neutron capture processes (s and r processes, respectively). The sites of the r and s-process are discussed, along with recent progress and their associated uncertainties. This review is mostly focused on the s-process which occurs in low and intermediate-mass stars which have masses up to about 8 solar masses (M⊙). We also discuss the intermediate-neutron capture process (or i-process), which may occur in AGB stars, accreting white dwarfs, and massive stars. The contribution of the i-process to the chemical evolution of elements in galaxies is as yet uncertain.

scholarly journals New models for the evolution of central stars of planetary nebulae: Faster and Brighter

2016 ◽  
Vol 12 (S323) ◽  
pp. 179-183
Author(s):  
Marcelo M. Miller Bertolami
Keyword(s):  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Short Article ◽  
Intermediate Mass Stars ◽  
New Models ◽  
Central Stars

AbstractThe post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The recent post-AGB evolutionary sequences computed by Miller Bertolami (2016) are at least three to ten times faster than those previously published by Vassiliadis & Wood (1994) and Blöcker (1995) which have been used in a large number of studies. This is true for the whole mass and metallicity range. The new models are also ~0.1–0.3 dex brighter than the previous models with similar remnant masses. In this short article we comment on the main reasons behind these differences, and discuss possible implications for other studies of post-AGB stars or planetary nebulae.

scholarly journals The Magellanic Clouds and Planetary Nebulae

1984 ◽  
Vol 108 ◽  
pp. 363-374
Author(s):  
Manuel Peimbert
Keyword(s):  
Emission Line ◽  
Chemical Evolution ◽  
Stellar Evolution ◽  
Central Star ◽  
Magellanic Clouds ◽  
Chemical Compositions ◽  
Intermediate Mass ◽  
Chemical Abundances ◽  
Line Intensities ◽  
Intermediate Mass Stars

A review of the statistics, emission line intensities, central star fluxes, radial velocities and chemical compositions of PN in the MC is given. From these data a discussion is made of: a) the distance scale, b) the envelope mass, c) the comparison between the observed chemical abundances and those predicted from stellar evolution models and, d) the effect that intermediate mass stars have on the chemical evolution of the MC and our galaxy.

scholarly journals Current Models for the Evolution of AGB Stars

2003 ◽  
Vol 209 ◽  
pp. 61-68
Author(s):  
Falk Herwig
Keyword(s):  
Stellar Evolution ◽  
Observational Studies ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Basic Properties ◽  
Intermediate Mass Stars ◽  
Stellar Models ◽  
Review Current

While the basic properties of AGB stellar evolution are well established, comprehensive observational studies of late phases of intermediate mass stars continue to generate puzzles for current stellar models. Here, I review current techniques to model AGB stars, and I discuss important aspects of current research of AGB (and post-AGB) stellar evolution with a particular focus on how these interrelate.

scholarly journals The Chemical Evolution of Magnesium Isotopic Abundances in the Solar Neighbourhood

2003 ◽  
Vol 20 (4) ◽  
pp. 340-344 ◽  
Author(s):  
Y. Fenner ◽  
B. K. Gibson ◽  
H.-c. Lee ◽  
A. I. Karakas ◽  
J. C. Lattanzio ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Galactic Disk ◽  
Asymptotic Giant Branch ◽  
Solar Neighbourhood ◽  
Asymptotic Giant Branch Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Isotopic Abundances ◽  
First Time ◽  
Giant Branch Stars

AbstractThe abundance of the neutron-rich magnesium isotopes observed in metal-poor stars is explained quantitatively with a chemical evolution model of the local Galaxy that considers — for the first time — the metallicity-dependent contribution from intermediate mass stars. Previous models that simulate the variation of Mg isotopic ratios with metallicity in the solar neighbourhood have attributed the production of 25Mg and 26Mg exclusively to hydrostatic burning in massive stars. These models match the data well for [Fe/H] > –1.0 but severely underestimate 25,26Mg/24Mg at lower metallicities. Earlier studies have noted that this discrepancy may indicate a significant role played by intermediate mass stars. Only recently have detailed calculations of intermediate mass stellar yields of 25Mg and 26Mg become available with which to test this hypothesis. In an extension of previous work, we present a model that successfully matches the Mg isotopic abundances in nearby Galactic disk stars through the incorporation of nucleosynthesis predictions of Mg isotopic production in asymptotic giant branch stars.

scholarly journals Asymptotic Giant Branch Evolution and the Initial-Final Mass Relation of Single CO White Dwarfs

2011 ◽  
Vol 7 (S281) ◽  
pp. 36-43
Author(s):  
Paola Marigo
Keyword(s):  
Mass Loss ◽  
White Dwarfs ◽  
Asymptotic Giant Branch ◽  
Mass Relation ◽  
Evolutionary Models ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Final Mass ◽  
The Impact

AbstractCombining recent mass determinations of Galactic CO white dwarfs and their progenitors with the latest evolutionary models for Asymptotic Giant Branch (AGB) stars, I review the initial-final mass relation (IFMR) of low- and intermediate-mass stars. In particular, I analyze the impact on the IFMR produced by a few critical processes characterizing the AGB phase, namely: the second and third dredge-up events, hot-bottom burning, and mass loss. Their dependence on metallicity and related theoretical uncertainties are briefly discussed.

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