A New Subclass of Carbon-Enhanced Metal-Poor Stars at Extremely Low Metallicity
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| Main Authors: | , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866914048733347840 |
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| author | Lee, Young Sun Beers, Timothy C. Hirai, Yutaka Hong, Jihye Jeong, Miji Kim, Changmin Kim, Young Kwang |
| author_facet | Lee, Young Sun Beers, Timothy C. Hirai, Yutaka Hong, Jihye Jeong, Miji Kim, Changmin Kim, Young Kwang |
| contents | We report the discovery of a new subclass of carbon-enhanced metal-poor (CEMP) stars, characterized by high absolute carbon abundances (A(C) > 7.39) and extremely low metallicity ([Fe/H] $<=$ -3.1) but notably lacking enhancements in neutron-capture elements, thus falling under the CEMP-no category. This population emerged from a detailed analysis of low-resolution spectroscopic data obtained from the Sloan Digital Sky Survey (SDSS) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), where the observed frequency trends with the decreasing metallicity of CEMP-s (s-process-enhanced) and CEMP-no (no neutron-capture enhanced) stars deviated from established expectations. In contrast to earlier findings, we observe a rise in high-A(C) stars below [Fe/H] = -3.1, which we interpret as a distinct group not accounted for in traditional CEMP classifications. Following the Yoon-Beers group classification, we define these stars as Group IV. Statistical modeling confirms their presence as a separate peak in the A(C) distribution, and available radial velocity data suggest that about 30% of Group IV stars may be binaries, indicating possible binary-related formation mechanisms. This discovery challenges the current CEMP-no star formation pathways and implies the existence of alternative or hybrid enrichment scenarios in the early Universe. High-resolution spectroscopic follow-up of Group IV candidates will be crucial for identifying their progenitors and understanding their evolutionary implications. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_16510 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A New Subclass of Carbon-Enhanced Metal-Poor Stars at Extremely Low Metallicity Lee, Young Sun Beers, Timothy C. Hirai, Yutaka Hong, Jihye Jeong, Miji Kim, Changmin Kim, Young Kwang Solar and Stellar Astrophysics Astrophysics of Galaxies We report the discovery of a new subclass of carbon-enhanced metal-poor (CEMP) stars, characterized by high absolute carbon abundances (A(C) > 7.39) and extremely low metallicity ([Fe/H] $<=$ -3.1) but notably lacking enhancements in neutron-capture elements, thus falling under the CEMP-no category. This population emerged from a detailed analysis of low-resolution spectroscopic data obtained from the Sloan Digital Sky Survey (SDSS) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), where the observed frequency trends with the decreasing metallicity of CEMP-s (s-process-enhanced) and CEMP-no (no neutron-capture enhanced) stars deviated from established expectations. In contrast to earlier findings, we observe a rise in high-A(C) stars below [Fe/H] = -3.1, which we interpret as a distinct group not accounted for in traditional CEMP classifications. Following the Yoon-Beers group classification, we define these stars as Group IV. Statistical modeling confirms their presence as a separate peak in the A(C) distribution, and available radial velocity data suggest that about 30% of Group IV stars may be binaries, indicating possible binary-related formation mechanisms. This discovery challenges the current CEMP-no star formation pathways and implies the existence of alternative or hybrid enrichment scenarios in the early Universe. High-resolution spectroscopic follow-up of Group IV candidates will be crucial for identifying their progenitors and understanding their evolutionary implications. |
| title | A New Subclass of Carbon-Enhanced Metal-Poor Stars at Extremely Low Metallicity |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.16510 |