发表机构
Astronomical Institute, Tohoku University; Division for the Establishment of Frontier Sciences, Organization for Advanced Studies, Tohoku University; National Institute for Fusion Science; Interdisciplinary Graduate School of Engineering Sciences, Kyushu University; Institute of Theoretical Physics and Astronomy, Vilnius University; Research Center for the Early Universe (RESCEU), Graduate School of Science, The University of Tokyo（东北大学天体物理研究所; 东北大学高级研究机构前沿科学科; 国立研究开发法人核融合科学研究所; 九州大学理工学研究科; 维尔纽斯大学理论物理与天文研究所; 东京大学理学研究院宇宙早期生命研究中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过GW170817晚期光谱构建解析模型，识别La III、Ce III和Te III的发射特征，约束了r过程元素丰度，发现内层抛射物中第一r过程峰受抑、重元素丰度增强。
AI 中文摘要
中子星合并事件GW170817提供了r过程核合成的第一个直接证据。其电磁对应体AT2017gfo的观测光谱呈现出若干特征，这些特征编码了所合成r过程元素的性质和丰度信息。在本研究中，我们探究了AT2017gfo的晚期星云相光谱特征，这些特征为抛射物的元素丰度提供了重要探针。我们构建了一个解析光谱模型，该模型通过允许跃迁和禁戒跃迁计算由碰撞激发离子的辐射衰变产生的发射特征。通过将我们的模型与AT2017gfo进行比较，我们确定La III和Ce III分别是1.4微米和1.6微米处发射特征的主要贡献者。我们还确认了Te III是先前工作中提出的2.1微米特征的主要贡献者。我们推断出质量分数为X(La)约0.025-0.05，X(Ce)约0.05-0.1，X(Te)约0.04-0.08，尽管由于辐射场的不确定性，La和Ce的丰度估计仍是初步的。根据Kr和Sb谱线的未探测结果，我们得出上限X(Kr)不超过0.03和X(Sb)不超过0.003。这些结果表明，GW170817内层抛射物中的核合成产生了相对于太阳r过程模式受到抑制的第一r过程峰和增强的重元素丰度，估计的镧系元素分数为X_LN约(3-6)乘以10的负2次方。我们的结论与重r过程元素的明显普遍性以及从r增强的贫金属星观测中推断出的镧系元素分数一致。
英文摘要
The neutron star merger event GW170817 provided the first direct evidence of $r$-process nucleosynthesis. Observed spectra of its electromagnetic counterpart AT2017gfo exhibited several features that encode information on the nature and abundance of the synthesized $r$-process elements. In this study, we investigate the late nebular-phase spectral features of AT2017gfo, which provide important probes of the elemental abundance of the ejecta. We construct an analytic spectral model that computes emission features produced by the radiative decay of collisionally excited ions through allowed and forbidden transitions. By comparing our model to AT2017gfo, we identify La III and Ce III as the main contributors to the emission features at $1.4\,μ{\rm m}$ and $1.6\,μ{\rm m}$, respectively. We also confirm Te III as the dominant contributor to the $2.1\,μ{\rm m}$ feature proposed in previous works. We infer mass fractions of $X({\rm La})\approx 0.025-0.05$, $X({\rm Ce})\approx 0.05-0.1$, and $X({\rm Te})\approx 0.04-0.08$, although the La and Ce abundance estimates remain tentative due to uncertainties in the radiation field. From the non-detections of Kr and Sb lines, we derive upper limits of $X({\rm Kr})\lesssim 0.03$ and $X({\rm Sb})\lesssim 0.003$. These results suggest that nucleosynthesis in the inner ejecta of GW170817 produced a suppressed first $r$-process peak and an enhanced heavy-element abundance compared to the solar $r$-process pattern, with an estimated lanthanide fraction of $X_{\rm LN}\approx (3-6) \times 10^{-2}$. Our conclusions are consistent with the apparent universality of heavy $r$-process elements and the lanthanide fraction inferred from observations of $r$-enhanced metal-poor stars.
Comments25 pages, 12 figures, 3 tables, accepted for publication in ApJ
