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arXiv 0904.3507astro-ph.SR
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半人马座欧米茄球状星团(NGC 5139)红巨星的大样本研究

A Large Sample Study of Red Giants in the Globular Cluster Omega Centauri (NGC 5139)

Christian I. Johnson, Catherine A. Pilachowski, R. Michael Rich, Jon P. Fulbright

摘要:

我们提出了几个轻,α,铁峰,和中子捕获元素的66红巨星分支(RGB)在银河系球状星团欧米茄半人马座恒星的丰度。我们的观测范围为12.0<V<13.5,主要集中在中间和富金属的RGB。我们发现金属度分布函数中至少有四个峰,位于[Fe/H]=-1.75、-1.45、-1.05和-0.75处,分别对应于我们样品的约55%、30%、10%和5%。此外,最富金属的恒星位于最中心的位置。Na和Al的相关性尽管表现出超过10倍的恒星间分散,但这些元素的分布似乎是金属丰度依赖的,并在[Fe/H]~-1.2处分开。约40-50%的恒星具有[Fe/H] <-1.2 have Na and Al abundances consistent with production solely in Type II supernovae and match observations of disk and halo stars at comparable metallicity. The remaining metal-poor stars are enhanced in Na and Al compared to their disk and halo counterparts and are mostly consistent with predicted yields from >5 M_sun渐近巨星分支(AGB)星。当[Fe/H]&gt;-1.2时,超过75%的恒星是Na/Al增强的,可能几乎完全由AGB喷出物形成。这些恒星中的大多数在给定铝丰度的情况下,钠含量比“正常”球状星团的值至少增加0.2 dex。我们样本中的所有恒星都富含α,并且具有太阳尺度的Fe峰丰度。Eu并不随金属丰度的变化而变化很大;然而,[La/Fe]在-0.4到+2之间变化,而[Fe/H]&gt;-1.5的恒星的[La/Eu]值则表明由s过程控制。四分之一的样品[La/Eu]&gt;+1,可能是二元体系中传质的结果。

英文摘要:

We present abundances of several light, alpha, Fe-peak, and neutron-capture elements for 66 red giant branch (RGB) stars in the Galactic globular cluster Omega Centauri. Our observations lie in the range 12.0<V<13.5 and focus on the intermediate and metal-rich RGBs. We find that there are at least four peaks in the metallicity distribution function at [Fe/H]=-1.75, -1.45, -1.05, and -0.75, which correspond to about 55%, 30%, 10%, and 5% of our sample, respectively. Additionally, the most metal-rich stars are the most centrally located. Na and Al are correlated despite exhibiting star-to-star dispersions of more than a factor of 10, but the distribution of those elements appears to be metallicity dependent and are divided at [Fe/H]~-1.2. About 40-50% of stars with [Fe/H]<-1.2 have Na and Al abundances consistent with production solely in Type II supernovae and match observations of disk and halo stars at comparable metallicity. The remaining metal-poor stars are enhanced in Na and Al compared to their disk and halo counterparts and are mostly consistent with predicted yields from >5 M_sun asymptotic giant branch (AGB) stars. At [Fe/H]>-1.2, more than 75% of the stars are Na/Al enhanced and may have formed almost exclusively from AGB ejecta. Most of these stars are enhanced in Na by at least 0.2 dex for a given Al abundance than would be expected based on "normal" globular cluster values. All stars in our sample are alpha-rich and have solar-scaled Fe-peak abundances. Eu does not vary extensively as a function of metallicity; however, [La/Fe] varies from about -0.4 to +2 and stars with [Fe/H]>-1.5 have [La/Eu] values indicating domination by the s-process. A quarter of our sample have [La/Eu]>+1 and may be the result of mass transfer in a binary system.

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