发表机构
Texas A&M University; Stockholm University; NSF NOIRLab; University of Notre Dame; University of Cambridge; Aarhus University（德克萨斯农工大学; 斯德哥尔摩大学; 美国国家光学红外天文研究实验室; 圣母大学; 剑桥大学; 奥胡斯大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
研究CEMP-no星的碳相关双星频率，通过对30颗CEMP-no星五年径向速度监测及结合文献数据，得到90颗星样本。发现高碳CEMP-no星双星频率高于低碳星，确定二者关系，还推导出四个新双星系统轨道参数。
AI 中文摘要
对银河系中最古老、金属丰度最低的恒星的研究证实了高碳富集与中子捕获元素次太阳丰度模式的共同丰度特征。所谓的碳增强无中子捕获元素（CEMP-no）星被推测为真正的第二代恒星，可能追踪宇宙中最早形成恒星的核合成。然而，确定CEMP-no星的双星性质对于理解其丰度模式至关重要。在之前对CEMP-no星的径向速度监测中，初步发现双星比例随碳增强而变化。本文展示了对30颗CEMP-no星进行五年径向速度监测的结果。结合文献数据，得到了90颗CEMP-no星的样本，以研究CEMP-no双星比例与碳富集的关系。发现高碳（$A(\mathrm{C}) \ge7.3$）CEMP-no星的总体双星频率为$50^{+13}_{-13}\%$，而低碳（$A(\mathrm{C}) <7.3$）星为$18^{+5}_{-4}\%$，首次在2$\sigma$置信水平上确定CEMP-no双星频率随碳含量有显著增加。对于已确认的双星系统，推导出四个新系统的轨道参数，结合文献数据，共有12个CEMP-no双星的轨道得到确定。在CEMP-no星的前身星背景下讨论了这些结果，特别探讨了这些双星系统中伴星的性质和质量转移的可能性。
英文摘要
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 ${\sim}30\%$ 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 ($A(\rm{C})\ge7.3$) CEMP-no stars, compared to $18^{+5}_{-4}\%$ for low-carbon ($A(\rm{C}) < 7.3$) 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.
CommentsAccepted to ApJ; 21 pages, 5 figures, 5 tables (Table A1 is available in full as an ancillary file)
