Michael R. Hayden, Sanjib Sharma, Joss Bland-Hawthorn, Lorenzo Spina, Sven Buder, Martin Asplund, Andrew R. Casey, Gayandhi M. De Silva, Valentina D'Orazi, Ken … 展开作者
Michael R. Hayden, Sanjib Sharma, Joss Bland-Hawthorn, Lorenzo Spina, Sven Buder, Martin Asplund, Andrew R. Casey, Gayandhi M. De Silva, Valentina D'Orazi, Ken C. Freeman, Janez Kos, Geraint F. Lewis, Jane Lin, Karin Lind, Sarah L. Martell, Katharine J. Schlesinger, Jeffrey D. Simpson, Daniel B. Zucker, Tomaz Zwitter, Boquan Chen, Klemen Cotar, Diane Feuillet, Jonti Horner, Meridith Joyce, Thomas Nordlander, Dennis Stello, Thorsten Tepper-Garcia, Yuan-sen Ting, Purmortal Wang, Rob Wittenmyer
Previous studies have found that the elemental abundances of a star correlate directly with its age and metallicity. Using this knowledge, we derive ages for a sample of 250,000 stars taken from GALAH DR3 using only their overall metallicity and chemical abundances. Stellar ages are estimated via the machine learning algorithm $XGBoost$, using main sequence turnoff stars with precise ages as our input training set. We find that the stellar ages for the bulk of the GALAH DR3 sample are accurate to 1-2 Gyr using this method. With these ages, we replicate many recent results on the age-kinematic trends of the nearby disk, including the age-velocity dispersion relationship of the solar neighborhood and the larger global velocity dispersion relations of the disk found using $Gaia$ and GALAH. The fact that chemical abundances alone can be used to determine a reliable age for a star have profound implications for the future study of the Galaxy as well as upcoming spectroscopic surveys. These results show that the chemical abundance variation at a given birth radius is quite small, and imply that strong chemical tagging of stars directly to birth clusters may prove difficult with our current elemental abundance precision. Our results highlight the need of spectroscopic surveys to deliver precision abundances for as many nucleosynthetic production sites as possible in order to estimate reliable ages for stars directly from their chemical abundances. Applying the methods outlined in this paper opens a new door into studies of the kinematic structure and evolution of the disk, as ages may potentially be estimated for a large fraction of stars in existing spectroscopic surveys. This would yield a sample of millions of stars with reliable age determinations, and allow precise constraints to be put on various kinematic processes in the disk, such as the efficiency and timescales of radial migration.
Milky Way's eccentric constituents with $Gaia$, APOGEE $\&$ GALAH
我们报告的结果的本地恒星晕的化学动力学空间跨越的丰度测量从APOGEE DR 17和GALAH DR 3的无监督分解。在我们的高斯混合模型中，只有四个独立的组成部分在太阳附近占主导地位，三个以前已知的$Aurora$，$Splash$和盖亚香肠/土卫二（GS/E）和一个新的，$Eos$。这四个星系中只有一个是吸积的，即GS/E，因此支持了早期的说法，即GS/E是银河系恒星晕的主要祖先。我们表明，$Aurora$是完全符合所谓的赫拉克勒斯合并的化学性质。在我们的分析中，没有预定义的化学选择削减应用，$Aurora$跨越了广泛的[Al/Fe]与金属丰度相关性指示快速化学富集在一个大规模的星系，年轻的银河系。由于其高平均值[Al/Fe]，被称为$Eos$的新晕组分被归类为$in situ$。$Eos$表现出强烈的演化作为[Fe/H]的函数，在那里它从最接近GS/E的最低[Fe/H]变化到与银河系低-$α$人口在其最高[Fe/H]无法区分。我们推测，至少有一部分银河系外薄盘是在被GS/E污染的气体中开始演化的，而$Eos$就是这一过程的证据。
Stellar nucleosynthesis in the era of large surveys: S-process polluted binaries in GALAH DR4
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 Astrofisico di Torino（意大利国家天体物理研究所都灵天文台）；Instituut voor Sterrenkunde, KU Leuven（荷语鲁汶大学恒星研究所）；Universidad Internacional de Valencia (VIU)（瓦伦西亚国际大学）；Université libre de Bruxelles (ULB)（布鲁塞尔自由大学）
Barium Stars Across the Milky Way: Probing Their Origins via the GALAH Survey
San Diego State University（圣地亚哥州立大学）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；University of Utah（犹他大学）；University of California Santa Cruz（加州大学圣克鲁兹分校）；Mullard Space Science Laboratory, University College London（伦敦大学学院穆拉德空间科学实验室）；Indiana University（印第安纳大学）；University of Wisconsin-Whitewater（威斯康星大学惠特沃分校）
Searching for and characterizing halo substructures with the GALAH DR4 survey
Stockholm University（斯德哥尔摩大学）；The Australian National University（澳大利亚国立大学）；The University of Sydney（悉尼大学）；University of Ljubljana（卢布尔雅那大学）；Macquarie University（麦考瑞大学）；ASTRO 3D（三维全天空天体物理学卓越中心）；University of New South Wales（新南威尔士大学）；Lund Observatory（隆德天文台）；International Space Science Institute–Beijing（国际空间科学研究所北京分部）；Space Telescope Science Institute（太空望远镜科学研究所）
恒星化学元素丰度测量的集合，以及精确的距离和轨道特性，为研究银河系的演化提供了高维数据。随着银河考古学与HERMES（GALAH）调查的第三次数据发布，我们发布了588571颗主要是附近恒星的678423光谱（81.2%的恒星在<2 kpc），用英澳望远镜的HERMES摄谱仪观测。这个版本（以下简称GALAH+ DR 3）包括GALAH第一阶段（亮、主、暗巡天，70%）、K2-HERMES（17%）、TESS-HERMES（5%）的所有观测结果，以及一部分辅助观测结果（8%），包括核球和>75个星团。利用改进后的光谱合成程序SME和一维MARCS模型大气，推导了恒星参数$T_\text{eff}$、$\log g$、[Fe/H]、$v_\text{mic}$、$v_\text{broad}$和$v_\text{rad}$。我们打破了光谱简并在我们的光谱分析与天体测量从$Gaia$ DR 2和测光从2 MASS。我们报告了30种不同元素（其中11种是基于非LTE计算）的丰度比[X/Fe]，涵盖了5种核合成途径。我们描述了验证的准确性和精度，特殊的明星/测量和建议使用我们的结果标记。我们的目录包括65%的矮星，34%的巨星和1%的其他/未分类的恒星。根据未标记的化学成分和年龄，我们发现62%的年轻低$α$，9%的年轻高$α$，27%的老年高$α$，和2%的恒星具有$\mathrm{[F…
$R$-process enhancements of Gaia-Enceladus in GALAH DR3
The dominant site of production of $r$ -process elements remains unclear despite recent observations of a neutron star merger. Observational constraints on the properties of the sites can be obtained by comparing $r$ -process abundances in different environments. The recent Gaia data releases and large samples from high-resolution optical spectroscopic surveys are enabling us to compare $r$ -process element abundances between stars formed in an accreted dwarf galaxy, Gaia-Enceladus, and those formed in the Milky Way. We aim to understand the origin of $r$ -process elements in Gaia-Enceladus. W…
A Catalog of 486 Barium Stars Identified in GALAH DR4
China West Normal University（西华师范大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Xiangtan University（湘潭大学）；Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Universidad de La Laguna（拉各斯大学）；Shandong University（山东大学）
Moving Groups in the Solar Neighborhood with Gaia, APOGEE, GALAH, and LAMOST: Dynamical Effects Gather Gas and the Ensuing Star Formation Plays an Important Role in Shaping the Stellar Velocity Distributions
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）
Modelling s-process chemical clocks: insights from high-precision Kepler data
Research School of Astronomy and Astrophysics, The Australian National University（澳大利亚国立大学天文与天体物理研究学院）；INAF – Osservatorio di Astrofisica e Sceinza dello Spazio（意大利国家天体物理研究所空间科学与天文台）；Institut für Kernphysik, Technische Universität Darmstadt（达姆施塔特工业大学核物理研究所）；INAF – Osservatorio Astronomico di Trieste（意大利国家天体物理研究所的里雅斯特天文台）
A Broken Clock Is Right Twice a Day: [Ce/Mg] Is Not a Universal Chemical Clock
The Ohio State University（俄亥俄州立大学）；Carnegie Institution for Science（卡内基科学学会）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；Lund Observatory（隆德天文台）；Johns Hopkins University（约翰斯·霍普金斯大学）；Flatiron Institute（平顿研究所）
