On the discovery of K-enhanced and possibly Mg-depleted stars throughout the Milky Way
Alex J. Kemp, Andrew R. Casey, Matthew T. Miles, Brodie J. Norfolk, John C. Lattanzio, Amanda I. Karakas, Kevin C. Schlaufman, Anna Y. Q. Ho, Christopher A. Tou… 展开作者
Alex J. Kemp, Andrew R. Casey, Matthew T. Miles, Brodie J. Norfolk, John C. Lattanzio, Amanda I. Karakas, Kevin C. Schlaufman, Anna Y. Q. Ho, Christopher A. Tout, Melissa Ness, Alexander P. Ji
Stars with unusual elemental abundances offer clues about rare astrophysical events or nucleosynthetic pathways. Stars with significantly depleted magnesium and enhanced potassium ([Mg/Fe] < -0.5; [K/Fe] > 1) have to date only been found in the massive globular cluster NGC 2419 and, to a lesser extent, NGC 2808. The origin of this abundance signature remains unknown, as does the reason for its apparent exclusivity to these two globular clusters. Here we present 112 field stars, identified from 454,180 LAMOST giants, that show significantly enhanced [K/Fe] and possibly depleted [Mg/Fe] abundance ratios. Our sample spans a wide range of metallicities (-1.5 < [Fe/H] < 0.3), yet none show abundance ratios of [K/Fe] or [Mg/Fe] that are as extreme as those observed in NGC 2419. If confirmed, the identified sample of stars represents evidence that the nucleosynthetic process producing the anomalous abundances ratios of [K/Fe] and [Mg/Fe] probably occurs at a wide range of metallicities. This would suggest that pollution scenarios that are limited to early epochs (such as Population III supernovae) are an unlikely explanation, although they cannot be ruled out entirely. This sample is expected to help guide modelling attempts to explain the origin of the Mg-K abundance signature.
Very Wide Binary Stars as the Primary Source of Stellar Collisions in the Galaxy
我们提出了数值模拟模拟的轨道演化非常宽的双星，对恒星分离超过1000 AU。由于其他经过的恒星和银河系潮汐的扰动，非常宽的双星的轨道偶尔会变得非常偏心，这迫使伴星之间发生近距离相遇（Kaib et al. 2013）。我们发现，这一过程导致了银河系中平均每1000-7500年发生一次非常宽的双星伴星之间的恒星碰撞。碰撞率的主要不确定性之一是近距离（但不是碰撞）近星点通道期间动态潮汐消散的能量。这种耗散为恒星碰撞提供了动力学障碍，并且可以将非常宽的双星转化为紧密或接触的双星。然而，对于任何合理的潮汐耗散模型，非常宽的双星是一个未实现的，并可能是我们银河系中恒星碰撞的主要来源。这样的碰撞应该发生在整个银河系的薄盘上。在非常宽的双星系统中的恒星碰撞应该会产生一小部分单一的、锂耗尽的、快速旋转的大质量恒星。
Abundances of planetary nebulae and evolved stars: Iron and sulfur depletion, and carbon and nitrogen enrichment, in low- and intermediate-mass stellar populations in the Milky Way
Statistics of the Chemical Composition of Solar Analog Stars and Links to Planet Formation
与邻近的太阳类似物相比，太阳被发现缺乏难熔（岩石形成）元素，这表明它是行星形成的潜在指标。由于消耗的幅度很小，以前的分析主要依赖于高信噪比的恒星光谱和严格的差分方法来确定元素丰度。我们提出了一种替代的，基于可能性的方法，可以应用于更大的样本的恒星，精度较低的丰度测定。我们利用阿帕奇点天文台星系演化实验（APOGEE-2）和恒星参数和化学丰度管道（ASPCAP DR 16）的约1700个太阳类似物的测量。通过开发一个分层混合模型的数据，我们把约束的元素丰度的统计特性，包括与冷凝温度和难熔元素耗尽的恒星的比例的相关性。我们发现了两个不同的种群的证据：一个是耗尽的恒星种群，构成了包括太阳在内的大多数太阳类似物，另一个是未耗尽的种群，占我们样本的10-30%。我们发现凝聚温度的相关性一般与更高精度的调查较小的恒星样本。这种趋势，如果与行星系统的形成有很强的联系，就提供了一种方法，可以将恒星化学丰度模式与银河系恒星的大样本行星系统联系起来。
Investigating star formation scenarios in the Milky Way using YSO distributions -- A pilot study
UNISA Centre for Astrophysics and Space Sciences (UCASS), College of Science, Engineering and Technology, University of South Africa（南非大学宇宙学与空间科学中心（UCASS），理工科学院）；Department of Physics and Astronomy, Faculty of Physical Sciences, University of Nigeria（尼日利亚大学物理科学学院物理与天文系）
Reassessing the low-$α$ massive sequence stars in Gaia RVS
Aryabhatta Research Institute of Observational Sciences（阿里亚巴塔观测科学研究所）；Division of Astrophysics, Department of Physics, Lund University（隆德大学物理系天体物理学分部）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉古纳大学）；INAF – Osservatorio Astronomico di Trieste（意大利国家天文台的里雅斯特天文台）；IFPU, Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Dipartimento di Fisica, Sezione di Astronomia, Università di Trieste（的里雅斯特大学物理系天文学部）；INFN Sezione di Trieste（意大利国家核物理研究所的里雅斯特分部）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学、蔚蓝海岸天文台、法国国家科学研究中心、拉格朗日实验室）
