An eclipsing CEMP candidate discovered in a search for dwarf carbon stars in post-common envelope binaries
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| Format: | Preprint |
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2026
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| _version_ | 1866918496929054720 |
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| author | McLennan, Jonathan A. G. Farihi, Jay Parsons, Steven G. |
| author_facet | McLennan, Jonathan A. G. Farihi, Jay Parsons, Steven G. |
| contents | Dwarf carbon stars are dominated by members of the Galactic halo and are thus likely carbon-enhanced metal-poor stars. In this work, a sample of 879 bona fide dwarf carbon stars are characterized by their ground-based light curves, and p<15 d modulation is found to be significant in 31 objects (3.5%), consistent with starspots and rotation in tidally-locked, post-common envelope binaries. Among these is an unambiguous halo star that is eclipsing every 1.224 d, and where the 30% eclipse depth rules out a white dwarf occulter. Available Gaia data do not indicate any tertiary in the eclipsing system, but this remains a possibility and follow-up data are necessary to determine the evolutionary history of this first eclipsing binary among carbon-enhanced stars. Four of the variable sources exhibit clear multi-year, quasi-sinusoidal trends indicative of magnetic-activity and starspot cycles in rapidly-rotating, dynamo-rejuvenated stars. These data support a picture where carbon pollution results from wind capture prior to Roche lobe overflow, and the orbital period distribution appears to be moderately shifted to longer periods than carbon-normal, low-mass stars in similar binaries. The band-combined approach adopted in this work may be more sensitive than prior work using single-bandpass light curves, where at most 19 of 34 binary candidates published by Roulston et al. (2021) are independently confirmed here. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_12024 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | An eclipsing CEMP candidate discovered in a search for dwarf carbon stars in post-common envelope binaries McLennan, Jonathan A. G. Farihi, Jay Parsons, Steven G. Solar and Stellar Astrophysics Dwarf carbon stars are dominated by members of the Galactic halo and are thus likely carbon-enhanced metal-poor stars. In this work, a sample of 879 bona fide dwarf carbon stars are characterized by their ground-based light curves, and p<15 d modulation is found to be significant in 31 objects (3.5%), consistent with starspots and rotation in tidally-locked, post-common envelope binaries. Among these is an unambiguous halo star that is eclipsing every 1.224 d, and where the 30% eclipse depth rules out a white dwarf occulter. Available Gaia data do not indicate any tertiary in the eclipsing system, but this remains a possibility and follow-up data are necessary to determine the evolutionary history of this first eclipsing binary among carbon-enhanced stars. Four of the variable sources exhibit clear multi-year, quasi-sinusoidal trends indicative of magnetic-activity and starspot cycles in rapidly-rotating, dynamo-rejuvenated stars. These data support a picture where carbon pollution results from wind capture prior to Roche lobe overflow, and the orbital period distribution appears to be moderately shifted to longer periods than carbon-normal, low-mass stars in similar binaries. The band-combined approach adopted in this work may be more sensitive than prior work using single-bandpass light curves, where at most 19 of 34 binary candidates published by Roulston et al. (2021) are independently confirmed here. |
| title | An eclipsing CEMP candidate discovered in a search for dwarf carbon stars in post-common envelope binaries |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2605.12024 |