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 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 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 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 Stellar yields for chemical evolution modelling

2013 ◽  
Vol 9 (S298) ◽  
pp. 142-153 ◽  
Author(s):  
Amanda I. Karakas
Keyword(s):  
Chemical Evolution ◽  
Surface Composition ◽  
Slow Neutron ◽  
Surface Enrichment ◽  
Intermediate Mass ◽  
Capture Process ◽  
Stellar Outflows ◽  
Evolved Stars ◽  
Intermediate Mass Stars ◽  
Low Metallicity

AbstractStellar yields are a key ingredient in chemical evolution models. Stars with masses as low as 0.9M⊙, which have an age less than that of our Galaxy at low metallicity, can contribute to the chemical evolution of elements. Stars less than about 8–10M⊙ experience recurrent mixing events that can significantly change the surface composition of the envelope. Evolved stars are observed with surface enrichment in carbon, nitrogen, fluorine, and heavy elements synthesized by the slow neutron capture process (the s-process). These stars release their nucleosynthesis products through stellar outflows or winds, in contrast to massive stars that explode as core-collapse supernovae. Here I review stellar yields for stars up to 10M⊙, including a brief discussion of their uncertainties and shortcomings. Finally, I discuss efforts by various groups to address these issues and to provide homogeneous yields for low and intermediate-mass stars covering a broad range of metallicities.

scholarly journals Following Fission Products in Explosive Astrophysical Environments

2020 ◽  
Vol 242 ◽  
pp. 04001
Author(s):  
T. M. Sprouse ◽  
M. R. Mumpower ◽  
R. Surman
Keyword(s):  
Neutron Capture ◽  
Extreme Environments ◽  
Fission Products ◽  
Nuclear Fission ◽  
Capture Process ◽  
Atomic Nuclei ◽  
Heaviest Elements ◽  
The Impact ◽  
The Universe

The astrophysical process by which the heaviest elements are formed in the universe is known as the rapid neutron capture process, or r process, of nucleosynthesis. The r process is characterized by the neutron capture and β− decay of short-lived, neutron-rich atomic nuclei; in suitably extreme environments, nuclear fission can also play a major role in determining the ensuing nucleosynthesis. In this work, we present the application of our recently developed nucleosynthesis tracing framework to precisely quantify the impact that neutron-induced and β− -delayed fission processes have in r-process environments that produce fissioning nuclei.

scholarly journals Near–Infrared Imaging of Proto-Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 340-340 ◽  
Author(s):  
R.E.S. Clegg ◽  
N. A. Walton ◽  
M.J. Barlow
Keyword(s):  
Molecular Hydrogen ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Preliminary Results ◽  
Near Ir ◽  
Intermediate Mass Stars ◽  
Hydrogen Lines

It is not really known how low and intermediate mass stars eject mass to form PNs. We present preliminary results from a programme of near–IR imaging, in which we study a sequence of objects, from extreme AGB stars through proto–planetaries to young, compact PNs. We aim to study the sequence of morphologies, to see where the onset of bipolar shaping occurs, and to use the IR molecular hydrogen lines to map neutral regions around ionized nebulae.

scholarly journals The s-process in stellar sites

2018 ◽  
Vol 184 ◽  
pp. 01004
Author(s):  
Sergio Cristallo
Keyword(s):  
Solar System ◽  
Neutron Capture ◽  
Slow Neutron ◽  
Heavy Elements ◽  
The Sun ◽  
Capture Process ◽  
The Universe ◽  
Pollution Episodes

Stars are marvellous caldrons where all the elements of the Universe (apartfrom hydrogen and helium) have been synthesized. The solar system chemical distri-butionis the result of many pollution episodes from already extinct stellar generations, occurred at different epochs before the Sun formation. Main nucleosynthesis channels re-sponsiblefor the formation of heavy elements are the rapid neutron capture process (ther-process) and the slow neutron capture process (the s-process). Hereafter, I will describethe theory of the s-process and the stellar sites where it is active.

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 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.

scholarly journals Dynamical and Chemical Evolution of IZw18

2004 ◽  
Vol 21 (2) ◽  
pp. 157-160
Author(s):  
Simone Recchi
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Dwarf Galaxy ◽  
Star Formation History ◽  
Intermediate Mass ◽  
Intermediate Mass Stars ◽  
Formation History ◽  
Type Ia ◽  
Ia Supernovae ◽  
Detailed Chemical

AbstractWe study the effect of different star formation regimes on the dynamical and chemical evolution of IZw18, the most metal-poor dwarf galaxy locally known. To do that we adopt a two-dimensional hydrocode coupled with detailed chemical yields originating from Type II and Type Ia supernovae and from intermediate-mass stars. Particular emphasis is devoted to the problem of mixing of metals. We conclude that, under particular conditions, cooling of metals occurs with a timescale of the order of 10 Myr, thus confirming the hypothesis of instantaneous mixing adopted in chemical evolution models. We try to draw conclusions about the star formation history and the age of the last burst in IZw18.

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