ABSTRACT

We report on the progress of our survey on ancient solar-type stars down to main-sequence effective temperatures T_eff ≥ 5300 K and within 42 pc of the Sun. High signal-to-noise, high-resolution spectroscopy is presented for a second major subset of the Population II (τ ≥ 12 Gyr) and the intermediate-disc stars (τ ≃ 10 Gyr) within that volume. In conjunction with updates and the analyses of the single and composite sample spectra, we discuss evidence for new companions or candidates from their radial velocities, chromospheric activities, lithium and barium enrichments, and we also draw attention to related sources in the Gaia DR2 data. Among the Population II stars we note a substantial fraction of degenerates, mass transfer, and merger systems that possibly amount to about 20 per cent of that population, with inherently important consequences on the involved stellar ages and the baryonic mass budget. At the present stage, the survey has reached a two-thirds level of local volume-completeness. Key to that objective will be the forthcoming Gaia data, in terms of new companions, companion masses, and precision parallaxes from orbital solutions, in particular at the sample periphery, where many of the sources inevitably reside. In an appendix we describe a subset of about fifty a priori survey candidates, whose analyses discard them as Population I stars.

中文翻译：

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关于古代太阳型恒星– II

摘要

我们报告了我们对古代太阳型恒星的调查进展，直至主要序列有效温度T _eff≥5300 K，距太阳42 pc以内。针对该体积内种群II（τ≥12 Gyr）的第二个主要子集和中间盘星（τ≥10 Gyr），提出了高信噪比的高分辨率光谱。结合单样本和复合样本光谱的更新和分析，我们讨论了新伴星或候选星的径向速度，色球活动，锂和钡富集的证据，并提请注意盖亚语中的相关来源DR2数据。在“二号种群”恒星中，我们注意到，相当一部分退化，质量转移和合并系统可能占该种群的20％，这对所涉恒星年龄和重磅物质预算具有内在的重要影响。在现阶段，调查已达到本地数量完整性的三分之二。该目标的关键将是即将出现的Gaia数据，这些数据来自轨道解的新伴星，伴星质量和精确视差，特别是在不可避免地存在许多源的样本外围。在附录中，我们描述了大约50个先验调查候选者的子集，其分析将它们视为人口I星。