A new route to massive hot subdwarfs: common envelope ejection from asymptotic giant branch stars
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| Main Authors: | , , , , , , , |
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| Format: | Preprint |
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2024
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| _version_ | 1866913205200093184 |
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| author | Li, Zhenwei Zhang, Yangyang Chen, Hailiang Ge, Hongwei Jiang, Dengkai Li, Jiangdan Chen, Xuefei Han, Zhanwen |
| author_facet | Li, Zhenwei Zhang, Yangyang Chen, Hailiang Ge, Hongwei Jiang, Dengkai Li, Jiangdan Chen, Xuefei Han, Zhanwen |
| contents | The hot subdwarf O/B stars (sdO/Bs) are known as extreme horizontal branch stars, which is of great importance in stellar evolution theory. The sdO/Bs are generally thought to have a helium-burning core and a thin hydrogen envelope $(M_{\rm env }<0.02M_\odot)$. In the canonical binary evolution scenario, sdO/Bs are considered to be the stripped cores of red giants. However, such a scenario cannot explain the recently discovered sdO/B binary, SMSS J1920, where the strong Ca H$\&$K lines in the spectrum are found. It suggests that this binary is likely originated from the recent ejection of common envelope (CE). In this {work}, we proposed a new formation channel of massive sdO/Bs, namely sdO/Bs produced from a CE ejection process with an asymptotic giant branch (AGB) star (hereafter AGB CE channel). We constructed the evolutionary model of sdO/Bs and successfully explained most of the important observed parameters of the sdO/B star in SMSS J1920, including the evolutionary age, sdO/B mass, effective temperature, surface gravity and surface helium abundance. The minimum sdO/B mass produced from the AGB CE channel is about $0.48M_\odot$. The evolutionary tracks in $\log T_{\rm eff}-\log g$ plane {may explain a fraction of the observational samples} with high-$\log T_{\rm eff}$ and low-$\log g$. Considering wind mass-loss of sdO/Bs, the model could produce helium-rich hot subdwarfs with $\log (n_{\rm He}/n_{\rm H})\gtrsim-1$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2401_12429 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | A new route to massive hot subdwarfs: common envelope ejection from asymptotic giant branch stars Li, Zhenwei Zhang, Yangyang Chen, Hailiang Ge, Hongwei Jiang, Dengkai Li, Jiangdan Chen, Xuefei Han, Zhanwen Solar and Stellar Astrophysics The hot subdwarf O/B stars (sdO/Bs) are known as extreme horizontal branch stars, which is of great importance in stellar evolution theory. The sdO/Bs are generally thought to have a helium-burning core and a thin hydrogen envelope $(M_{\rm env }<0.02M_\odot)$. In the canonical binary evolution scenario, sdO/Bs are considered to be the stripped cores of red giants. However, such a scenario cannot explain the recently discovered sdO/B binary, SMSS J1920, where the strong Ca H$\&$K lines in the spectrum are found. It suggests that this binary is likely originated from the recent ejection of common envelope (CE). In this {work}, we proposed a new formation channel of massive sdO/Bs, namely sdO/Bs produced from a CE ejection process with an asymptotic giant branch (AGB) star (hereafter AGB CE channel). We constructed the evolutionary model of sdO/Bs and successfully explained most of the important observed parameters of the sdO/B star in SMSS J1920, including the evolutionary age, sdO/B mass, effective temperature, surface gravity and surface helium abundance. The minimum sdO/B mass produced from the AGB CE channel is about $0.48M_\odot$. The evolutionary tracks in $\log T_{\rm eff}-\log g$ plane {may explain a fraction of the observational samples} with high-$\log T_{\rm eff}$ and low-$\log g$. Considering wind mass-loss of sdO/Bs, the model could produce helium-rich hot subdwarfs with $\log (n_{\rm He}/n_{\rm H})\gtrsim-1$. |
| title | A new route to massive hot subdwarfs: common envelope ejection from asymptotic giant branch stars |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2401.12429 |