What we do and do not know about the s-process in AGB stars

Lattanzio, John C.; Lugaro, Maria

doi:10.1016/j.nuclphysa.2005.05.088

Cited by 22 publications

(22 citation statements)

References 23 publications

(69 reference statements)

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“…Ba is one of the most massive s-process (slow neutron capture) elements synthesized by low-mass (≈1-3 M ) AGB stars (e.g., Lattanzio & Lugaro 2005 Karakas et al 2014) due to closed neutron shells. Sr, Ba (isotopes from 128 Ba to 140 Ba), and Pb are located at these peaks and are used to represent the scaling of the s-process elements.…”

Section: Results and Conclusionmentioning

confidence: 99%

Stellar laboratories

Rauch

Werner

Quinet

et al. 2014

A&A

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Context. For the spectral analysis of high-resolution and high-signal-to-noise (S/N) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation.Aims. Reliable Ba v-vii oscillator strengths are used to identify Ba lines in the spectra of the DA-type white dwarf G191−B2B and the DO-type white dwarf RE 0503−289 and to determine their photospheric Ba abundances.Methods. We newly calculated Ba v-vii oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for the analysis of Ba lines exhibited in high-resolution and high-S/N UV observations of G191−B2B and RE 0503−289.Results. For the first time, we identified highly ionized Ba in the spectra of hot white dwarfs. We detected Ba vi and Ba vii lines in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of RE 0503−289. The Ba vi/Ba vii ionization equilibrium is well reproduced with the previously determined effective temperature of 70 000 K and surface gravity of log g = 7.5. The Ba abundance is 3.5 ± 0.5 × 10 −4 (mass fraction, about 23 000 times the solar value). In the FUSE spectrum of G191−B2B, we identified the strongest Ba vii line (at 993.41 Å) only, and determined a Ba abundance of 4.0 ± 0.5 × 10−6 (about 265 times solar). Conclusions. Reliable measurements and calculations of atomic data are a pre-requisite for stellar-atmosphere modeling. Observed Ba vi-vii line profiles in two white dwarfs' (G191−B2B and RE 0503−289) far-ultraviolet spectra were well reproduced with our newly calculated oscillator strengths. This allowed to determine the photospheric Ba abundance of these two stars precisely.

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Section: Results and Conclusionmentioning

confidence: 99%

Stellar laboratories

Rauch

Werner

Quinet

et al. 2014

A&A

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“…According to the most recent models, the 13 C(α,n) 16 O reaction is the preferred neutron source for masses around 1−3 M , while for more massive stars (i.e. M > ∼ 3−4 M ) neutrons are thought to be mainly released through the 22 Ne(α,n) 25 Mg reaction (see, for example, Busso et al 1999 andLugaro 2005, for a recent review). In the literature, there is strong evidence that most Galactic AGB stars enriched in s-process elements have masses around 1−3 M , where the 13 C(α,n) 16 O reaction is the neutron donor (e.g.…”

Section: Introductionmentioning

confidence: 99%

Lithium and zirconium abundances in massive Galactic O-rich AGB stars

García–Hernández¹,

García-Lario²,

Plez³

et al. 2006

A&A

121

135

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Lithium and zirconium abundances (the latter taken as representative of s-process enrichment) are determined for a large sample of massive Galactic O-rich AGB stars, for which high-resolution optical spectroscopy has been obtained (R ∼ 40 000−50 000). This was done by computing synthetic spectra based on classical hydrostatic model atmospheres for cool stars and using extensive line lists. The results are discussed in the framework of "hot bottom burning" (HBB) and nucleosynthesis models. The complete sample is studied for various observational properties such as the position of the stars in the IRAS two-colour diagram ([12] − [25] vs.[25] − [60]), Galactic distribution, expansion velocity (derived from the OH maser emission), and period of variability (when available). We conclude that a considerable fraction of these sources are actually massive AGB stars (M > 3−4 M ) experiencing HBB, as deduced from the strong Li overabundances we found. A comparison of our results with similar studies carried out in the past for the Magellanic Clouds (MCs) reveals that, in contrast to MC AGB stars, our Galactic sample does not show any indication of s-process element enrichment. The differences observed are explained as a consequence of metallicity effects. Finally, we discuss the results obtained in the framework of stellar evolution by comparing our results with the data available in the literature for Galactic post-AGB stars and PNe.

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“…Elements of interest at these peaks for representing the scaling of s-process elements include strontium, barium, and lead. Good recent compilations of the main s-process can be found in Lattanzio & Lugaro (2005), and a good review of the s-process can be found in Käppeler et al (2010).…”

Section: Weak S-processmentioning

confidence: 99%

“…In massive stars the weak s-process yields are constrained by both the initial CNO abundance, which is responsible for providing a neutron source, and also the initial Fe abundance which supplies the seeds for neutron capture (Pignatari et al 2010). The initial Fe abundance is also important in intermediate and low-mass asymptotic giant branch (AGB) stars for seeding the main s-process yields (Käppeler et al 1989(Käppeler et al , 2010Lattanzio & Lugaro 2005). The detailed stellar abundances affect the opacity of the star (e.g., the The Opacity Project Team 1995), which in turn will affect the structure as well as mass and angular momentum loss, which in turn changes the late stellar evolution.…”

Section: Introductionmentioning

confidence: 99%

Metallicity-Dependent Galactic Isotopic Decomposition for Nucleosynthesis

West

Heger

2013

ApJ

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All stellar evolution models for nucleosynthesis require an initial isotopic abundance set to use as a starting point. Generally, our knowledge of isotopic abundances of stars is fairly incomplete except for the Sun. We present a first model for a complete average isotopic decomposition as a function of metallicity. Our model is based on the underlying nuclear astrophysics processes, and is fitted to observational data, rather than traditional forward galactic chemical evolution modeling which integrates stellar yields beginning from big bang nucleosynthesis. We first decompose the isotopic solar abundance pattern into contributions from astrophysical sources. Each contribution is then assumed to scale as a function of metallicity. The resulting total isotopic abundances are summed into elemental abundances and fitted to available halo and disk stellar data to constrain the model's free parameter values. This procedure allows us to use available elemental observational data to reconstruct and constrain both the much needed complete isotopic evolution that is not accessible to current observations, and the underlying astrophysical processes. As an example, our model finds a best fit for Type Ia contributing 0.7 to the solar Fe abundance, and Type Ia onset occurring at [Fe/H] −1.1, in agreement with typical values.

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What we do and do not know about the s-process in AGB stars

Cited by 22 publications

References 23 publications

Stellar laboratories

Stellar laboratories

Lithium and zirconium abundances in massive Galactic O-rich AGB stars

Metallicity-Dependent Galactic Isotopic Decomposition for Nucleosynthesis

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