The Odd Isotope Fractions of Barium in the Strongly r-process-enhanced (r-II) Stars*

Cui, Wenyuan; Jiang, Xiaohua; Shi, Jianrong; Zhao, Gang; Zhang, Bo

doi:10.3847/1538-4357/aaa75f

Cited by 6 publications

(4 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Various studies relate the measurement of isotopic ratios in metalpoor stars. The most discussed ratio is 12 C/ 13 C (e.g., Aoki et al 2002;Spite et al 2006;Masseron et al 2010;Hansen et al 2016), but barium isotopic fractions (e.g., Magain 1995;Gallagher et al 2012;Wenyuan et al 2018), as well as europium (Sneden et al 2002;Aoki et al 2003a,b;Roederer et al 2008), samarium (Lundqvist et al 2007;Zhang et al 2010;Roederer et al 2008), and neodymium (Roederer et al 2008) were also largely discussed.…”

Section: Isotopic Ratios In R/s-starsmentioning

confidence: 99%

The intermediate neutron capture process

Choplin

Siess

Goriely

2021

A&A

View full text Add to dashboard Cite

Context. Results from observations report a growing number of metal-poor stars showing an abundance pattern midway between the s- and r-processes. These so-called r/s-stars raise the need for an intermediate neutron capture process (i-process), which is thought to result from the ingestion of protons in a convective helium-burning region, but whose astrophysical site is still largely debated. Aims. We investigate whether an i-process during the asymptotic giant branch (AGB) phase of low-metallicity low-mass stars can develop and whether it can explain the abundances of observed r/s-stars. Methods. We computed a 1 M⊙ model at [Fe/H] = −2.5 with the stellar evolution code STAREVOL, using a nuclear network of 1091 species (at maximum) coupled to the transport processes. The impact of the temporal and spatial resolutions on the resulting abundances was assessed. We also identified key elements and isotopic ratios that are specific to i-process nucleosynthesis and carried out a detailed comparison between our model and a sample of r/s-stars. Results. At the beginning of the AGB phase, during the third thermal pulse, the helium driven convection zone is able to penetrate the hydrogen-rich layers. The subsequent proton ingestion leads to a strong neutron burst with neutron densities of ∼4.3 × 1014 cm−3 at the origin of the synthesis of i-process elements. The nuclear energy released by proton burning in the helium-burning convective shell strongly affects the internal structure: the thermal pulse splits and after approximately ten years the upper part of the convection zone merges with the convective envelope. The surface carbon abundance is enhanced by more than 3 dex. This leads to an increase in the opacity, which triggers a strong mass loss and prevents any further thermal pulse. Our numerical tests indicate that the i-process elemental distribution is not strongly affected by the temporal and spatial resolution used to compute the stellar models, but typical uncertainties of ±0.3 dex on individual abundances are found. We show that specific isotopic ratios of Ba, Nd, Sm, and Eu can represent good tracers of i-process nucleosynthesis. Finally, an extended comparison with 14 selected r/s-stars show that the observed composition patterns can be well reproduced by our i-process AGB model. Conclusions. A rich i-process nucleosynthesis can take place during the early AGB phase of low-metallicity low-mass stars and explain the elemental distribution of most of the r/s-stars, but cannot account for the high level of enrichment of the giant stars in a scenario involving pollution by a former AGB companion.

show abstract

Section: Isotopic Ratios In R/s-starsmentioning

confidence: 99%

The intermediate neutron capture process

Choplin

Siess

Goriely

2021

A&A

View full text Add to dashboard Cite

show abstract

“…Fig. 4 shows the f odd,Ba measured in five r-II stars with strongly enhanced r-process [68] along with the value calculated using experimental P xn (red band). The figure also shows the range of f odd,Ba calculated using P xn predicted by the three models considered in this paper (shaded band).…”

mentioning

confidence: 96%

“…4. Odd-mass Ba isotopic fraction f odd,Ba for five rprocess enhanced stars (r-II) labeled with their names [68,69] compared to f odd,Ba calculated using experimental Pxn (red band) and a range of f odd,Ba calculated using Pxn predicted by the three models considered in this paper (shaded area), with FRDM+QRPA+HF resulting in the upper limit and RHB+pnQRPA+HF in the lower one. f odd,Ba for solar (dashed line) and pure s-process (dash-dotted line) abundances [70].…”

mentioning

confidence: 99%

β -Delayed One and Two Neutron Emission Probabilities Southeast of Sn132 and the Odd-Even Systematics in
Phong¹,
Nishimura²,
Lorusso³
et al. 2022
Phys. Rev. Lett.

View full text Add to dashboard Cite

math xmlns="http://www.w3.org/1998/Math/MathML" display="inline">mi>β/mi>/math>-Delayed One and Two Neutron Emission Probabilities Southeast of math xmlns="http://www.w3.org/1998/Math/MathML" display="inline">mrow>mmultiscripts>mrow>mi>Sn/mi>/ mrow>mprescripts>/mprescripts>none>/none>mrow>mn >132/mn>/mrow>/mmultiscripts>/mrow>/math> and the Odd-Even Systematics in math xmlns="http://www.w3.org/1998/Math/MathML" display="inline">mi>r/mi>/math>-Process Nuclide Abundances V. H. Phong et al.

show abstract

“…Various studies relate the measurement of isotopic ratios in metal-poor stars. The most discussed ratio is 12 C/ 13 C (e.g., Aoki et al 2002;Spite et al 2006;Masseron et al 2010;Hansen et al 2016), but barium isotopic fractions (e.g., Magain 1995;Gallagher et al 2012;Wenyuan et al 2018), as well as europium (Sneden et al 2002;Aoki et al 2003a,b;Roederer et al 2008), samarium (Lundqvist et al 2007;Zhang et al 2010;Roederer et al 2008), and neodymium (Roederer et al 2008) were also largely discussed.…”

Section: Isotopic Ratios In R/s-starsmentioning

confidence: 99%

The intermediate neutron capture process. I. Development of the i-process in low-metallicity low-mass AGB stars

Choplin,

Siess,

Goriely

2021

Preprint

View full text Add to dashboard Cite

Context. Results from observations report a growing number of metal-poor stars showing an abundance pattern midway between the s-and r-processes. These so-called r/s-stars raise the need for an intermediate neutron capture process (i-process), which is thought to result from the ingestion of protons in a convective helium-burning region, but whose astrophysical site is still largely debated. Aims. We investigate whether an i-process during the asymptotic giant branch (AGB) phase of low-metallicity low-mass stars can develop and whether it can explain the abundances of observed r/s-stars. Methods. We computed a 1 M model at [Fe/H] = −2.5 with the stellar evolution code STAREVOL, using a nuclear network of 1091 species (at maximum) coupled to the transport processes. The impact of the temporal and spatial resolutions on the resulting abundances was assessed. We also identified key elements and isotopic ratios that are specific to i-process nucleosynthesis and carried out a detailed comparison between our model and a sample of r/s-stars. Results. At the beginning of the AGB phase, during the third thermal pulse, the helium driven convection zone is able to penetrate the hydrogen-rich layers. The subsequent proton ingestion leads to a strong neutron burst with neutron densities of ∼ 4.3 × 10 14 cm −3 at the origin of the synthesis of i-process elements. The nuclear energy released by proton burning in the helium-burning convective shell strongly affects the internal structure: the thermal pulse splits and after approximately ten years the upper part of the convection zone merges with the convective envelope. The surface carbon abundance is enhanced by more than 3 dex. This leads to an increase in the opacity, which triggers a strong mass loss and prevents any further thermal pulse. Our numerical tests indicate that the i-process elemental distribution is not strongly affected by the temporal and spatial resolution used to compute the stellar models, but typical uncertainties of ±0.3 dex on individual abundances are found. We show that specific isotopic ratios of Ba, Nd, Sm, and Eu can represent good tracers of i-process nucleosynthesis. Finally, an extended comparison with 14 selected r/s-stars show that the observed composition patterns can be well reproduced by our i-process AGB model. Conclusions. A rich i-process nucleosynthesis can take place during the early AGB phase of low-metallicity low-mass stars and explain the elemental distribution of most of the r/s-stars, but cannot account for the high level of enrichment of the giant stars in a scenario involving pollution by a former AGB companion.

show abstract

The Odd Isotope Fractions of Barium in the Strongly r-process-enhanced (r-II) Stars*

Cited by 6 publications

References 48 publications

The intermediate neutron capture process

The intermediate neutron capture process

β -Delayed One and Two Neutron Emission Probabilities Southeast of Sn132 and the Odd-Even Systematics in
Phong¹,
Nishimura²,
Lorusso³
et al. 2022
Phys. Rev. Lett.

The intermediate neutron capture process. I. Development of the i-process in low-metallicity low-mass AGB stars

Contact Info

Product

Resources

About

The Odd Isotope Fractions of Barium in the Strongly r-process-enhanced (r-II) Stars*

Cited by 6 publications

References 48 publications

The intermediate neutron capture process

The intermediate neutron capture process

β -Delayed One and Two Neutron Emission Probabilities Southeast of Sn132 and the Odd-Even Systematics in Phong1, Nishimura2, Lorusso3 et al. 2022Phys. Rev. Lett.

The intermediate neutron capture process. I. Development of the i-process in low-metallicity low-mass AGB stars

Contact Info

Product

Resources

About

β -Delayed One and Two Neutron Emission Probabilities Southeast of Sn132 and the Odd-Even Systematics in
Phong¹,
Nishimura²,
Lorusso³
et al. 2022
Phys. Rev. Lett.