Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis
Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis
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DOI：
10.3847/1538-4357/ab9643
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发表时间：
2020-05
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通讯作者：
T. Hansen;J. Marshall;J. Simon;Tian Li;R. Bernstein;A. Pace;P. Ferguson;D. Nagasawa;K. Kuehn;D. Carollo;M. Geha;D. James;A. Walker;H. Diehl;M. Aguena;S. Allam;S. Ávila;E. Bertin;D. Brooks;E. Buckley-Geer;D. Burke;A. Rosell;M. Kind;J. Carretero;M. Costanzi;L. Costa;S. Desai;J. Vicente;P. Doel;K. Eckert;T. Eifler;S. Everett;I. Ferrero;J. Frieman;J. García-Bellido;E. Gaztañaga;D. Gerdes;D. Gruen;R. Gruendl;J. Gschwend;G. Gutiérrez;S. Hinton;D. Hollowood;K. Honscheid;N. Kuropatkin;M. Maia;M. March;R. Miquel;A. Palmese;F. Paz-Chinchón;A. Plazas;E. Sánchez;B. Santiago;V. Scarpine;S. Serrano;M. Smith;M. Soares-Santos;E. Suchyta;M. Swanson;G. Tarlé;T. Varga;R. Wilkinson
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作者：
T. Hansen;J. Marshall;J. Simon;Tian Li;R. Bernstein;A. Pace;P. Ferguson;D. Nagasawa;K. Kuehn;D. Carollo;M. Geha;D. James;A. Walker;H. Diehl;M. Aguena;S. Allam;S. Ávila;E. Bertin;D. Brooks;E. Buckley-Geer;D. Burke;A. Rosell;M. Kind;J. Carretero;M. Costanzi;L. Costa;S. Desai;J. Vicente;P. Doel;K. Eckert;T. Eifler;S. Everett;I. Ferrero;J. Frieman;J. García-Bellido;E. Gaztañaga;D. Gerdes;D. Gruen;R. Gruendl;J. Gschwend;G. Gutiérrez;S. Hinton;D. Hollowood;K. Honscheid;N. Kuropatkin;M. Maia;M. March;R. Miquel;A. Palmese;F. Paz-Chinchón;A. Plazas;E. Sánchez;B. Santiago;V. Scarpine;S. Serrano;M. Smith;M. Soares-Santos;E. Suchyta;M. Swanson;G. Tarlé;T. Varga;R. Wilkinson
我们对超微弱矮矮星系（UFD）天鹤座 II 巨分支顶部的三颗最亮成员恒星进行了详细的丰度分析。与其他 UFD 星系和银河系 (MW) 晕中的贫金属恒星相比，所有恒星都表现出高于预期的 [Mg/Ca] 比率。高质量（20 M⊙）核心塌陷超新星中的核合成已被证明可以产生这种特征。这个小样本（三颗）恒星的丰度表明天鹤二号的化学富集可能是通过大量的高质量恒星演化而发生的，并且与头重脚轻的初始质量函数的框架一致。然而，由于只有三颗恒星，不能排除丰度模式是星系早期随机化学富集的结果。三颗恒星中金属含量最高的恒星还拥有少量增强的快速中子俘获（r-过程）元素。这颗恒星中 r 过程元素的丰度模式与太阳系的按比例 r 过程模式以及其他矮星系和 MW 晕中的 r 过程增强型恒星相匹配，暗示这些元素在一系列环境中具有共同起源。目前提出的所有 r 过程元素生产的天体物理地点都与大质量恒星有关，因此天鹤 II 可能的头重脚轻的初始质量函数将增加任何这些事件发生的可能性。星系的 α 过程元素富集和 r 过程元素富集之间的时间延迟有利于中子星合并作为天鹤 II 中 r 过程元素的起源。
We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( 20 M⊙) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the α and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II.