r-process Abundance Patterns in the Globular Cluster M92

IF 4.8 2区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS
Evan N. Kirby, Alexander P. Ji, Mikhail Kovalev
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Abstract

Abstract Whereas light-element abundance variations are a hallmark of globular clusters, there is little evidence for variations in neutron-capture elements. A significant exception is M15, which shows a star-to-star dispersion in neutron-capture abundances of at least one order of magnitude. The literature contains evidence both for and against a neutron-capture dispersion in M92. We conducted an analysis of archival Keck/HIRES spectra of 35 stars in M92, 29 of which are giants, which we use exclusively for our conclusions. M92 conforms to the abundance variations typical of massive clusters. Like other globular clusters, its neutron-capture abundances were generated by the r -process. We confirm a star-to-star dispersion in r -process abundances. Unlike M15, the dispersion is limited to “first-generation” (low-Na, high-Mg) stars, and the dispersion is smaller for Sr, Y, and Zr than for Ba and the lanthanides. This is the first detection of a relation between light-element and neutron-capture abundances in a globular cluster. We propose that a source of the main r -process polluted the cluster shortly before or concurrently with the first generation of star formation. The heavier r -process abundances were inhomogeneously distributed while the first-generation stars were forming. The second-generation stars formed after several crossing times (∼0.8 Myr); hence, the second generation shows no r -process dispersion. This scenario imposes a minimum temporal separation of 0.8 Myr between the first and second generations.
球状星团M92的r-过程丰度模式
虽然轻元素丰度的变化是球状星团的一个标志,但很少有证据表明中子捕获元素的变化。一个重要的例外是M15,它显示出中子捕获丰度至少一个数量级的恒星间色散。文献中有支持和反对M92中子捕获色散的证据。我们对M92中35颗恒星的凯克/雇佣光谱档案进行了分析,其中29颗是巨星,我们的结论只使用这些恒星。M92符合典型的大质量星团的丰度变化。像其他球状星团一样,它的中子捕获丰度是由r过程产生的。我们确认了r过程丰度的星间色散。与M15不同的是,色散仅限于“第一代”(低na,高mg)恒星,Sr, Y和Zr的色散小于Ba和镧系元素。这是第一次探测到球状星团中轻元素和中子捕获丰度之间的关系。我们提出,在第一代恒星形成前不久或同时,主r过程的一个来源污染了星团。在第一代恒星形成时,较重的r过程丰度分布不均匀。第二代恒星经过几次交叉(~ 0.8 Myr)形成;因此,第二代没有r过程分散。这种情况要求第一代和第二代之间的最小时间间隔为0.8 Myr。
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来源期刊
Astrophysical Journal
Astrophysical Journal 地学天文-天文与天体物理
CiteScore
8.40
自引率
30.60%
发文量
2854
审稿时长
1 months
期刊介绍: The Astrophysical Journal is the foremost research journal in the world devoted to recent developments, discoveries, and theories in astronomy and astrophysics.
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