The Carbon-Dependent Binary Frequency of CEMP-no Stars
Abstract
Studies of the oldest and most metal-poor stars in the Milky Way confirm a common chemical signature of high carbon abundances and subsolar neutron-capture enrichment. The so-called CEMP-no stars are speculated to be bona fide population II stars, potentially tracing the nucleosynthesis of the first stars in the universe. However, constraining the binary nature of CEMP-no stars is crucial for understanding their origins. The binary fraction of CEMP-no stars has tentatively been found to vary with carbon enhancement, independent of metallicity. Here we present the results of radial-velocity monitoring of 30 CEMP-no stars over five years, increasing the total number of CEMP-no stars with a constrained binary status by ∼30% in order to better investigate the CEMP-no binary fraction as a function of carbon. Combining our results with literature data, we find an overall binary frequency of 50+13−13% among high-carbon (A(C)≥7.3) CEMP-no stars, compared to 18+5−4% for low-carbon (A(C) < 7.3) stars, establishing a statistically significant increase in the CEMP-no binary frequency as a function of carbon for the first time. Our results indicate no correlation between metallicity and binary frequency. Additionally, we derive orbital parameters for three new CEMP-no stars in binary systems and estimate secondary masses for these stars as well as seven binaries from the literature. We discuss these mass estimates in the context of investigating the nature of the unseen companions and the plausibility of a mass-transfer formation channel for high-carbon CEMP-no stars.
Versions
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BibTeX
@misc{dixon2026carbondependent,
title = {{The Carbon-Dependent Binary Frequency of CEMP-no Stars}},
author = {John D. Dixon and Terese T. Hansen and Jennifer Marshall and Vinicius M. Placco and Timothy C. Beers and Anke Ardern-Arentsen and Birgitta Nordström and Lauren N. Aldoroty and Jared Cathey and Peter S. Ferguson and Katherine Kristofek and Karin Lind and Hudson Malone and Ferner Moreno and Jessica Myron and Alexander H. Riley and Else Starkenburg and Kaitlin B. Webber},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.13020},
eprint = {2607.13020},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.13020},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Carbon-Dependent Binary Frequency of CEMP-no Stars
AU - John D. Dixon
AU - Terese T. Hansen
AU - Jennifer Marshall
AU - Vinicius M. Placco
AU - Timothy C. Beers
AU - Anke Ardern-Arentsen
AU - Birgitta Nordström
AU - Lauren N. Aldoroty
AU - Jared Cathey
AU - Peter S. Ferguson
AU - Katherine Kristofek
AU - Karin Lind
AU - Hudson Malone
AU - Ferner Moreno
AU - Jessica Myron
AU - Alexander H. Riley
AU - Else Starkenburg
AU - Kaitlin B. Webber
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2607.13020
UR - https://arxiv.org/abs/2607.13020
AB - Studies of the oldest and most metal-poor stars in the Milky Way confirm a common chemical signature of high carbon abundances and subsolar neutron-capture enrichment. The so-called CEMP-no stars are speculated to be bona fide population II stars, potentially tracing the nucleosynthesis of the first stars in the universe. However, constraining the binary nature of CEMP-no stars is crucial for understanding their origins. The binary fraction of CEMP-no stars has tentatively been found to vary with carbon enhancement, independent of metallicity. Here we present the results of radial-velocity monitoring of 30 CEMP-no stars over five years, increasing the total number of CEMP-no stars with a constrained binary status by ∼30% in order to better investigate the CEMP-no binary fraction as a function of carbon. Combining our results with literature data, we find an overall binary frequency of 50^+13_−13% among high-carbon (A(C)≥7.3) CEMP-no stars, compared to 18^+5_−4% for low-carbon (A(C) < 7.3) stars, establishing a statistically significant increase in the CEMP-no binary frequency as a function of carbon for the first time. Our results indicate no correlation between metallicity and binary frequency. Additionally, we derive orbital parameters for three new CEMP-no stars in binary systems and estimate secondary masses for these stars as well as seven binaries from the literature. We discuss these mass estimates in the context of investigating the nature of the unseen companions and the plausibility of a mass-transfer formation channel for high-carbon CEMP-no stars.
ER -