Galactic Chemical Evolution of the s Process from AGB Stars

AbstractWe follow the chemical evolution of the Galaxy for the s elements using a Galactic chemical evolution (GCE) model, as already discussed by Travaglio et al. (1999, 2001, 2004), with a full updated network and refined asymptotic giant branch (AGB) models. Calculations of the s contribution to each isotope at the epoch of the formation of the solar system is determined by following the GCE contribution by AGB stars only. Then, using the r-process residual method we determine for each isotope their solar system r-process fraction, and recalculate the GCE contribution of heavy elements accounting for both the s and r process. We compare our results with spectroscopic abundances at various metallicities of [Sr,Y,Zr/Fe], of [Ba,La/Fe], of [Pb/Fe], typical of the three s-process peaks, as well as of [Eu/Fe], which in turn is a typical r-process element. Analysis of the various uncertainties involved in these calculations are discussed.

Download Full-text

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316004725 ◽

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.

Download Full-text

Galactic Chemical Evolution of Radioactive Isotopes with an s-process Contribution

The Astrophysical Journal ◽

10.3847/1538-4357/ac31b0 ◽

2022 ◽

Vol 924 (1) ◽

pp. 10

Author(s):

Thomas C. L. Trueman ◽

Benoit Côté ◽

Andrés Yagüe López ◽

Jacqueline den Hartogh ◽

Marco Pignatari ◽

...

Keyword(s):

Chemical Evolution ◽

Average Length ◽

Asymptotic Giant Branch ◽

Radioactive Isotopes ◽

Agb Stars ◽

Galactic Chemical Evolution ◽

Early Solar System ◽

Self Consistent ◽

Consistent Solution ◽

The Mean

Abstract Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives of 0.1–100 Myr existed in the early solar system (ESS). We investigate the ESS origin of 107Pd, 135Cs, and 182Hf, which are produced by slow neutron captures (the s-process) in asymptotic giant branch (AGB) stars. We modeled the Galactic abundances of these SLRs using the OMEGA+ galactic chemical evolution (GCE) code and two sets of mass- and metallicity-dependent AGB nucleosynthesis yields (Monash and FRUITY). Depending on the ratio of the mean-life τ of the SLR to the average length of time between the formations of AGB progenitors γ, we calculate timescales relevant for the birth of the Sun. If τ/γ ≳ 2, we predict self-consistent isolation times between 9 and 26 Myr by decaying the GCE predicted 107Pd/108Pd, 135Cs/133Cs, and 182Hf/180Hf ratios to their respective ESS ratios. The predicted 107Pd/182Hf ratio indicates that our GCE models are missing 9%–73% of 107Pd and 108Pd in the ESS. This missing component may have come from AGB stars of higher metallicity than those that contributed to the ESS in our GCE code. If τ/γ ≲ 0.3, we calculate instead the time (T LE) from the last nucleosynthesis event that added the SLRs into the presolar matter to the formation of the oldest solids in the ESS. For the 2 M ⊙, Z = 0.01 Monash model we find a self-consistent solution of T LE = 25.5 Myr.

Download Full-text

Heavy Element Nucleosynthesis

EPJ Web of Conferences ◽

10.1051/epjconf/201818401007 ◽

2018 ◽

Vol 184 ◽

pp. 01007

Author(s):

Mounib F. El Eid

Keyword(s):

Chemical Evolution ◽

Neutron Capture ◽

Heavy Element ◽

Slow Neutron ◽

Heavy Elements ◽

Galactic Chemical Evolution ◽

Physical Processes ◽

The Galaxy ◽

R Process

This contribution deals with the important subject of the nucleosynthesis of heavy elements in the Galaxy. After an overview of several observational features, the physical processes responsible mainly for the formation of heavy elements will be described and linked to possible stellar sites and to galactic chemical evolution. In particular, we focus on the neutron-capture processes, namely the s-process (slow neutron capture) and the r-process (rapid neutron capture) and discuss some problems in connection with their sites and their outcome. The aim is to give a brief overview on the exciting subject of the heavy element nucleosynthesis in the Galaxy, emphasizing its importance to trace the galactic chemical evolution and illustrating the challenge of this subject.

Download Full-text

Fundamental problems and basic tests of stellar evolution theory — The case of carbon stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900030503 ◽

1984 ◽

Vol 105 ◽

pp. 3-19

Author(s):

Icko Iben

Keyword(s):

Solar System ◽

Theoretical Work ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Carbon Stars ◽

Core Mass ◽

Convective Envelope ◽

Thermal Pulse ◽

R Process ◽

Neutron Rich Isotopes

Carbon stars are thought to be in the asymptotic giant branch (AGB) phase of evolution, alternately burning hydrogen and helium in shells above an electron-degenerate carbon-oxygen (CO) core. The excess of carbon relative to oxygen at the surfaces of these stars is thought to be due to convective dredge-up which occurs following a thermal pulse. During a thermal pulse, carbon and neutron-rich isotopes are made in a convective helium-burning zone. In model stars of large CO core mass, the source of neutrons for producing the neutron-rich isotopes is the 22Ne(α, n)25Mg reaction and the isotopes are produced in the solar system s-process distribution. In models of small core mass, the 13C(α, n) 16O reaction is thought to be responsible for the release of neutrons, and the resultant distribution of neutron-rich isotopes is expected to vary considerably from one star to the next, with the distribution in isolated instances possibly resembling the solar system distribution of r-process isotopes. After the dredge-up phase following each pulse, the 13C is made by the reactions 12C(p,γ) 13N(β+ v) 13C in a zone of large 12C abundance and small 1H abundance that has been established by semiconvective mixing during the dredge-up phase. There is qualitative accord between the properties of carbon stars in the Magellanic Clouds and properties of model stars, but considerably more theoretical work is required before a quantitative match is achieved.The observed paucity of AGB stars more luminous than MBOL ∼ −6 is interpreted to mean that the AGB lifetime of a star more luminous than this is at least a factor of ten smaller than the AGB lifetime of stars less luminous than this, or, at most 105 yr. Since, with current estimates of the 22Ne(α, n)25Mg reaction rate R22, only AGB model stars more luminous than MBOL ∼ −6 can produce s-process isotopes in the solar system distribution, it is inferred that either (1) the current estimates of R22 are too small by one to two orders of magnitude, allowing less luminous AGB stars to contribute, (2) the solar system distribution is not equivalent to the average Galactic distribution, being rather the consequence of a unique injection into the protosolar nebula of matter from a massive intermediate-mass AGB star, or (3) the estimates of the temperatures in the convective shell that are given by extant models are too low by, sav, 10 or 15 percent.The absence of carbon stars more luminous than MBOL ∼ −6 is suggested to be due primarily to the fact that ∼ 106 yr of AGB evolution is necessary to produce surface C/O > 1, rather than to be due to the burning of dredged-up carbon into nitrogen at the base of the convective envelope during the interpulse quiescent hydrogen-burning phase. Thus, the positive correlation between the nitrogen and helium abundances in planetary nebulae is perhaps primarily a consequence of the second dredge-up episode rather than a consequence of processes occurring during the thermally pulsing phase.

Download Full-text

Abundance ratios & ages of stellar populations in HARPS-GTO sample

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317006081 ◽

2017 ◽

Vol 12 (S330) ◽

pp. 156-159 ◽

Cited By ~ 1

Author(s):

E. Delgado Mena ◽

M. Tsantaki ◽

V. Zh. Adibekyan ◽

S. G. Sousa ◽

N. C. Santos ◽

...

Keyword(s):

Chemical Evolution ◽

Thin Disk ◽

Thick Disk ◽

Heavy Elements ◽

Galactic Chemical Evolution ◽

Chemical Abundances ◽

Homogeneous Sample ◽

Different Populations ◽

Search Program ◽

Cu And Zn

AbstractIn this work we present chemical abundances of heavy elements (Z>28) for a homogeneous sample of 1059 stars from HARPS planet search program. We also derive ages using parallaxes from Hipparcos and Gaia DR1 to compare the results. We study the [X/Fe] ratios for different populations and compare them with models of Galactic chemical evolution. We find that thick disk stars are chemically disjunt for Zn adn Eu. Moreover, the high-alpha metal-rich population presents an interesting behaviour, with clear overabundances of Cu and Zn and lower abundances of Y and Ba with respect to thin disk stars. Several abundance ratios present a significant correlation with age for chemically separated thin disk stars (regardless of their metallicity) but thick disk stars do not present that behaviour. Moreover, at supersolar metallicities the trends with age tend to be weaker for several elements.

Download Full-text

(Pre)-white dwarf stars as measuring tools for yields of AGB nucleosynthesis

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320000617 ◽

2019 ◽

Vol 15 (S357) ◽

pp. 158-161

Author(s):

Lisa Löbling

Keyword(s):

White Dwarf ◽

Neutron Capture ◽

Convection Zone ◽

Slow Neutron ◽

Asymptotic Giant Branch ◽

Heavy Elements ◽

Agb Stars ◽

Subsequent Evolution ◽

Dwarf Stars ◽

White Dwarf Stars

AbstractIn the helium-rich intershell region of asymptotic giant branch (AGB) stars, slow neutron-capture nucleosynthesis produces heavy elements beyond iron. If the stars experience a final-flash of the He-burning shell, a pulse-driven convection zone establishes, the stars become hydrogen-deficient and exhibit former intershell material at their surfaces. In their subsequent evolution towards the white-dwarf cooling sequence, but still at constant luminosity, a strong stellar wind prevents diffusion to wipe out the information about AGB yields. We present and interpret the analysis results of hydrogen-rich and -deficient post-AGB stars, discuss difficulties in their analysis and review the implications on the understanding of post-AGB evolution.

Download Full-text

Stardust in meteorites: A link between stars and the Solar System

Proceedings of the International Astronomical Union ◽

10.1017/s174392130802190x ◽

2008 ◽

Vol 4 (S251) ◽

pp. 341-342

Author(s):

Ernst Zinner

Keyword(s):

Solar System ◽

Interplanetary Dust ◽

Asymptotic Giant Branch ◽

Dust Particles ◽

Red Giants ◽

Agb Stars ◽

Interplanetary Dust Particles ◽

Mixing Processes ◽

Isotopic Compositions ◽

Stellar Sources

AbstractUltimately, all of the solids in the Solar System, including ourselves, consist of elements that were made in stars by stellar nucelosynthesis. However, most of the material from many different stellar sources that went into the making of the Solar System was thoroughly mixed, obliterating any information about its origin. An exception are tiny grains of preserved stardust found in primitive meteorites, micrometeorites, and interplanetary dust particles. These μm- and sub-μm-sized presolar grains are recognized as stardust by their isotopic compositions, which are completely different from those of the Solar System. They condensed in outflows from late-type stars and in SN ejecta and were included in meteorites, from which they can be isolated and studied for their isotopic compositions in the laboratory. Thus these grains constitute a link between us and our stellar ancestors. They provide new information on stellar evolution, nucleosynthesis, mixing processes in asymptotic giant branch (AGB) stars and supernovae, and galactic chemical evolution. Red giants, AGB stars, Type II supernovae, and possibly novae have been identified as stellar sources of the grains. Stardust phases identified so far include silicates, oxides such as corundum, spinel, and hibonite, graphite, silicon carbide, silicon nitride, titanium carbide, and Fe-Ni metal.

Download Full-text

Heavy elements in planetary nebulae: A theorist's gold mine

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312010824 ◽

2011 ◽

Vol 7 (S283) ◽

pp. 127-130

Author(s):

Amanda I. Karakas ◽

Maria Lugaro

Keyword(s):

Neutron Capture ◽

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Heavy Elements ◽

Gold Mine ◽

Agb Stars ◽

Capture Process ◽

Wide Range ◽

Model Predictions

AbstractObservations of planetary nebulae have revealed a wealth of information about the composition of heavy elements synthesized by the slow neutron capture process (the s process). In some of these nebulae the abundances of neutron-capture elements are enriched by factors of 10 to 30 times the solar value, indicating that these elements were produced in the progenitor star while it was on the asymptotic giant branch (AGB). In this proceedings we summarize results of our recent full s-process network predictions covering a wide range of progenitor masses and metallicities. We compare our model predictions to observations and show how this can provide important insights into nucleosynthesis processes occurring deep within AGB stars.

Download Full-text

Volatile loss, Differentiation and Collisions: Key to the Composition of Rocky Exoplanets

10.5194/epsc2020-387 ◽

2020 ◽

Author(s):

Amy Bonsor ◽

John Harrison ◽

Oliver Shorttle ◽

Philip Carter ◽

Mihkel Kama ◽

...

Keyword(s):

Solar System ◽

Chemical Evolution ◽

White Dwarf ◽

Thermal Processing ◽

White Dwarfs ◽

Bulk Composition ◽

Galactic Chemical Evolution ◽

Common Process ◽

Planetary Bodies ◽

Volatile Loss

Volatile loss, Differentiation and Collisions: Key to the Composition of Rocky Exoplanets Many of the key characteristics and geology of our planet Earth today were determined during the planet&#8217;s formation. What about rocky exoplanets? How does rocky planet formation determine the properties, composition, geology and ultimately, presence of life on rocky exoplanets?&#160; In this talk I will discuss projects that investigate the link between rocky planet formation and the composition of rocky exoplanets. This work utilises unique observations that provide us with the bulk composition of rocky exoplanetary material. These observations come from the old, faint remnants of stars like our Sun, known as white dwarfs.&#160; White dwarfs should have clean hydrogen or helium atmospheres. This means that planetary bodies as small as asteroids can show up in the white dwarf&#8217;s atmosphere. Metallic species such as Fe, Mg or Ca provide the bulk composition of the accreted body. Several thousand polluted white dwarfs are now known. Models indicate that outer planetary systems, like our Solar System beyond Mars, should survive the star&#8217;s evolution to the white dwarf phase. Scattering is a common process, and any bodies that are scattered inwards, a bit like sun-grazing comets in our Solar System, would show up in the white dwarf atmosphere. What determines the composition of the rocky exoplanetary bodies accreted by white dwarfs?&#160; Models presented in Harrison et al, 2018, 2020 (submitted) find that the abundances observed in the atmospheres of white dwarfs can be explained by three key processes, notably galactic chemical evolution, loss of volatiles (thermal processing) and large scale melting&#160; which leads to the segregation of material between the core, mantle and crust. Galactic chemical evolution determines the initial composition of the planet forming material. Thermal processing determines the loss of volatiles, be that CO and other gases, water, or moderate volatile species such as Na. Collisions between planetary bodies that have differentiated to form a core can lead to fragments dominated by core-rich or mantle-rich material.&#160; Core-Mantle differentiation is a common process in exoplanetary systems High abundances of siderophile (iron-loving) compared to lithophile (silicate loving) speeches in some polluted white dwarfs indicate that accretion of a planetary body composed primarily of material from a planetary core (or alternatively mantle). Harrison et al, 2020, based on data from Hollands et al, 2017, 2018, present several examples of systems with extreme abundances, core-rich, mantle-rich or crust-rich.&#160; Bonsor et al, 2020 concludes that most polluted white dwarfs (>60%) have accreted the fragment of a differentiated exoplanetesimal.&#160; Post-Nebula volatilisation in exoplanetary bodies Mn and Na trace the loss of volatiles in planetary bodies. The difference in behaviour of Mn and Na under oxidising/reducing conditions makes them a strong indicator of the conditions prevalent when volatile loss occurred. Mn/Na for the Moon/Mars indicate post-Nebula volatile loss&#160; (Siebert et al, 2018). Harrison et al, 2020, in prep, provides the first evidence of post-nebula volatilisation in exoplanetary bodies utilising the Mn/Na abundances of polluted white dwarfs.&#160;

Download Full-text