Barium lines in high-quality spectra of two metal-poor giants in the Galactic halo
<i>Context.<i/> Theoretical results showed the possibility that neutron capture elements were produced in the early Universe by two different sources: a frequent <i>s<i/>-process source hosted by rotating massive stars, and a rare <i>r<i/>-process source hosted mo...
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| Main Authors: | , , , , , , , , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
11 August 2021
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| In: |
Astronomy and astrophysics
Year: 2021, Volume: 654, Pages: 1-12 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202141355 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1051/0004-6361/202141355 Verlag, lizenzpflichtig, Volltext: https://www.aanda.org/articles/aa/abs/2021/10/aa41355-21/aa41355-21.html 
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| Author Notes: | G. Cescutti, C. Morossi, M. Franchini, P. Di Marcantonio, C. Chiappini, M. Steffen, M. Valentini, P. François, N. Christlieb, C. Cortés, C. Kobayashi, and E. Depagne |
| Summary: | <i>Context.<i/> Theoretical results showed the possibility that neutron capture elements were produced in the early Universe by two different sources: a frequent <i>s<i/>-process source hosted by rotating massive stars, and a rare <i>r<i/>-process source hosted most likely by neutron star mergers. The two sources produce barium with different isotopic compositions.<i>Aims.<i/> We aim to investigate the lines of barium in two halo stars, HD 6268 and HD 4306. The spectra present an exquisite quality, both in terms of resolution (<i>R<i/> > 100 000) and signal-to-noise (~400). Due to hyperfine splitting (hfs) effects, barium lines are expected to show slightly different profiles depending on the barium isotopic fraction.<i>Methods.<i/> We applied a standard local thermodynamic equilibrium synthesis of the barium lines. We compared the synthetic results assuming an <i>s<i/>-process isotopic pattern or an <i>r<i/>-process isotopic pattern for the two barium lines for each star that exhibited hfs. We also applied a methodology, less dependent on the accuracy of the theoretical Ba hfs structure, that transforms the lines of HD 4306 into those we would observe if its atmospheric parameter values (i.e. <i>T<i/><sub>eff<sub/>, log <i>g<i/>, micro- and macro-turbulence, <i>V<i/> sin <i>i<i/>, and Ba abundance) were the same as those of HD 6268.<i>Results.<i/> With both methods, our results show that the barium lines with hfs effects of HD 4306 are in agreement with an <i>s<i/>-process composition and the lines in HD 6268 have a different profile, which is most likely linked to the presence of an <i>r<i/>-process isotopic pattern.<i>Conclusions.<i/> Two lines of barium of HD 6268 and HD 4306 seem to confirm the theoretical expectation that both <i>r<i/>-process events and also <i>s<i/>-process contribution by rotating massive stars have polluted the ancient halo of our Galaxy. |
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| Item Description: | Gesehen am 09.02.2022 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/202141355 |