We present a chemical abundance distribution study in 14 $α$, odd-Z, even-Z, light, and Fe-peak elements of approximately 3200 intermediate metallicity giant stars from the APOGEE survey. The main aim of our analysis is to explore the Galactic disk-halo transition region between -1.20 $<$ [Fe/H] $<$ -0.55 as a means to study chemical difference (and similarities) between these components. In this paper, we show that there is an $α$-poor and $α$-rich sequence within both the metal-poor and intermediate metallicity regions. Using the Galactic rest-frame radial velocity and spatial positions, we further separate our sample into the canonical Galactic components. We then studied the abundances ratios, of Mg, Ti, Si, Ca, O, S, Al, C+N, Na, Ni, Mn, V, and K for each of the components and found the following: (1) the $α$-poor halo subgroup is chemically distinct in the $α$-elements (particularly O, Mg, and S), Al, C+N, and Ni from the $α$-rich halo, consistent with the literature confirming the existence of an $α$-poor accreted halo population; (2) the canonical thick disk and halo are not chemically distinct in all elements indicating a smooth transition between the thick disk and halo; (3) a subsample of the $α$-poor stars at metallicities as low as [Fe/H] $\sim$ -0.85 dex are chemically and dynamically consistent with the thin disk indicating that the thin disk may extend to lower metallicities than previously thought, and (4) that the location of the most metal-poor thin disk stars are consistent with a negative radial metallicity gradient. Finally, we used our analysis to suggest a new set of chemical abundance planes ([$α$/Fe], [C+N/Fe], [Al/Fe], and [Mg/Mn]) that may be able to chemically label the Galactic components in a clean and efficient way independent of kinematics.
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）
Chemical tagging with APOGEE, MUSE, and HST: constraints on the formation of $ω$ Centauri
Liverpool John Moores University（利物浦约翰摩尔斯大学）；University of Liverpool（利物浦大学）；NOIRLab（美国国家光学红外天文研究实验室）；University of Edinburgh（爱丁堡大学）；Centro de Estudios de Física del Cosmos de Aragón (CEFCA)（阿拉贡宇宙物理研究中心）；University of Virginia（弗吉尼亚大学）；Steward Observatory, University of Arizona（亚利桑那大学斯图德天文台）；ELTE Eötvös Loránd University（罗兰大学）
Two faces of Gaia-Sausage-Enceladus: Mining the chemical abundance space with graph attention networks
INAF - Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；Dipartimento di Fisica e Astronomia, Università di Padova（帕多瓦大学物理与天文学系）；INAF - Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；INAF - IASF-Milano（意大利国家天体物理研究所米兰天文物理研究所）；University of Birmingham（伯明翰大学）；INAF - Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）
On the connection between nitrogen-enhanced field stars and the Galactic globular clusters
Institute of Astronomy, University of Cambridge（剑桥大学天文研究所）；School of Mathematics and Physics, The University of Queensland（昆士兰大学数理学院）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；Department of Astronomy and Astrophysics, The University of Chicago（芝加哥大学天文学与天体物理学系）
