s-process Enriched Post-AGB Star J003643.94-723722.1 in the SMC with an Extreme C/O Ratio and the First Precise Detection of Lead
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| Format: | Preprint |
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2025
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| _version_ | 1866908521250947072 |
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| author | Menon, Meghna Kamath, Devika Mohorian, Maksym Amarsi, Anish M. Vescovi, Diego Cristallo, Sergio Karakas, Amanda Van Winckel, Hans Ventura, Paolo |
| author_facet | Menon, Meghna Kamath, Devika Mohorian, Maksym Amarsi, Anish M. Vescovi, Diego Cristallo, Sergio Karakas, Amanda Van Winckel, Hans Ventura, Paolo |
| contents | Post-asymptotic giant branch (post-AGB) stars are exquisite tracers of s-process nucleosynthesis via their surface abundances. We present a comprehensive analysis of J003643.94$-$723722.1 (J003643), a single SMC post-AGB star, using high-resolution UVES/VLT spectra analysed with E-iSpec. We find C/O = 16.21 and $[\mathrm{s}/\mathrm{Fe}]=2.09\pm0.20 \mathrm{dex}$. We also report the first direct Pb detection in a post-AGB star from the Pb II 5608.853 A line, with $[\mathrm{Pb}/\mathrm{Fe}]=3.18\,\mathrm{dex}$. Comparison with post-AGB samples in the Galaxy and Magellanic Clouds reveals that J003643 has an unusually high C/O ratio. J003643's $[\mathrm{C}/\mathrm{Fe}]=1.33\pm0.14 \mathrm{dex}$ and $[\mathrm{s}/\mathrm{Fe}]=2.09\pm0.20\,\mathrm{dex}$ are consistent with third dredge-up enrichment, but its $[\mathrm{O}/\mathrm{Fe}]=-0.08\pm0.20\,\mathrm{dex}$ is low relative to objects of similar $[\mathrm{C}/\mathrm{Fe}]$ and $[\mathrm{Fe}/\mathrm{H}]$. Together with $[α/\mathrm{Fe}]\approx0\,\mathrm{dex}$ at $[\mathrm{Fe}/\mathrm{H}]\approx-1\,\mathrm{dex}$, consistent with SMC chemical evolution, this indicates the high C/O chiefly reflects oxygen deficiency rather than exceptional carbon enrichment. Additionally, we compare the full abundance pattern with yields from ATON, MONASH and FRUITY (the latter two with post-processing nucleosynthesis). Most elements are reproduced, but Pb is strongly underpredicted, highlighting a persistent gap in models of heavy-element production in AGB stars. The photospheric chemistry of J003643 adds to the growing diversity among post-AGB stars and underscores the complexity of AGB nucleosynthesis. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_05015 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | s-process Enriched Post-AGB Star J003643.94-723722.1 in the SMC with an Extreme C/O Ratio and the First Precise Detection of Lead Menon, Meghna Kamath, Devika Mohorian, Maksym Amarsi, Anish M. Vescovi, Diego Cristallo, Sergio Karakas, Amanda Van Winckel, Hans Ventura, Paolo Solar and Stellar Astrophysics Post-asymptotic giant branch (post-AGB) stars are exquisite tracers of s-process nucleosynthesis via their surface abundances. We present a comprehensive analysis of J003643.94$-$723722.1 (J003643), a single SMC post-AGB star, using high-resolution UVES/VLT spectra analysed with E-iSpec. We find C/O = 16.21 and $[\mathrm{s}/\mathrm{Fe}]=2.09\pm0.20 \mathrm{dex}$. We also report the first direct Pb detection in a post-AGB star from the Pb II 5608.853 A line, with $[\mathrm{Pb}/\mathrm{Fe}]=3.18\,\mathrm{dex}$. Comparison with post-AGB samples in the Galaxy and Magellanic Clouds reveals that J003643 has an unusually high C/O ratio. J003643's $[\mathrm{C}/\mathrm{Fe}]=1.33\pm0.14 \mathrm{dex}$ and $[\mathrm{s}/\mathrm{Fe}]=2.09\pm0.20\,\mathrm{dex}$ are consistent with third dredge-up enrichment, but its $[\mathrm{O}/\mathrm{Fe}]=-0.08\pm0.20\,\mathrm{dex}$ is low relative to objects of similar $[\mathrm{C}/\mathrm{Fe}]$ and $[\mathrm{Fe}/\mathrm{H}]$. Together with $[α/\mathrm{Fe}]\approx0\,\mathrm{dex}$ at $[\mathrm{Fe}/\mathrm{H}]\approx-1\,\mathrm{dex}$, consistent with SMC chemical evolution, this indicates the high C/O chiefly reflects oxygen deficiency rather than exceptional carbon enrichment. Additionally, we compare the full abundance pattern with yields from ATON, MONASH and FRUITY (the latter two with post-processing nucleosynthesis). Most elements are reproduced, but Pb is strongly underpredicted, highlighting a persistent gap in models of heavy-element production in AGB stars. The photospheric chemistry of J003643 adds to the growing diversity among post-AGB stars and underscores the complexity of AGB nucleosynthesis. |
| title | s-process Enriched Post-AGB Star J003643.94-723722.1 in the SMC with an Extreme C/O Ratio and the First Precise Detection of Lead |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2509.05015 |