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arXiv 1102.5312astro-ph.GAastro-ph.SR
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Milky Way星系同位素比的演化

The Evolution of Isotope Ratios in the Milky Way Galaxy

Chiaki Kobayashi, Amanda I. Karakas, Hideyuki Umeda

摘要:

同位素比值为研究恒星演化、超新星和星系化学演化的细节打开了一扇新的窗口。我们提出的元素丰度(从C到Zn)在太阳附近的同位素比的演变,凸起,晕,厚盘,使用化学演化模型与更新的渐近巨分支(AGB)恒星和核心塌陷超新星的产量。由于初始母体质量和金属丰度对元素生成的影响,每种元素的演化历史是不同的。在凸起和厚盘中,恒星形成的时间尺度比太阳附近的短,导致更高的[α/Fe]比率。同样,Ia型超新星在这些区域的贡献较小,导致[Mn/Fe]比值较低。同样在核球中,[(Na,Al,P,Cl,K,Sc,Cu,Zn)/Fe]丰度较高,这是由于金属丰度对核塌缩超新星产生元素的影响。根据我们的预测,有可能发现富含金属的恒星([Fe/H]>-1),这些恒星是在早期宇宙中快速形成的结果。晕的化学富集时间尺度比太阳附近的长,因此[(C,F)/Fe]和12 C/13 C的比值较高,这是由于低质量AGB星的显著贡献。虽然[α/Fe]和[Mn/Fe]比值与太阳附近相同,但[(Na,Al,P,Cl,K,Sc,Cu,Zn)/Fe]比值预计会更低。此外,我们预测的同位素比值,如24 Mg/25,26 Mg是较大的,因为低金属丰度超新星的贡献。利用同位素比率,可以选择在化学富集效率低的系统中形成的恒星,例如在我们银河系中吸积的卫星星系。

英文摘要:

Isotope ratios have opened a new window into the study of the details of stellar evolution, supernovae, and galactic chemical evolution. We present the evolution of the isotope ratios of elemental abundances (from C to Zn) in the solar neighbourhood, bulge, halo, and thick disk, using chemical evolution models with updated yields of Asymptotic Giant Branch (AGB) stars and core-collapse supernovae. The evolutionary history of each element is different owing to the effects of the initial progenitor mass and metallicity on element production. In the bulge and thick disk the star formation timescale is shorter than in the solar neighbourhood, leading to higher [alpha/Fe] ratios. Likewise, the smaller contribution from Type Ia supernovae in these regions leads to lower [Mn/Fe] ratios. Also in the bulge, the abundances of [(Na, Al, P, Cl, K, Sc, Cu, Zn)/Fe] are higher because of the effect of metallicity on element production from core-collapse supernovae. According to our predictions, it is possible to find metal-rich stars ([Fe/H]>-1) that formed in the early Universe as a result of rapid star formation. The chemical enrichment timescale of the halo is longer than in the solar neighbourhood, and consequently the ratios of [(C, F)/Fe] and 12C/13C are higher owing to a significant contribution from low-mass AGB stars. While the [alpha/Fe] and [Mn/Fe] ratios are the same as in the solar neighbourhood, the [(Na, Al, P, Cl, K, Sc, Cu, Zn)/Fe] ratios are predicted to be lower. Furthermore, we predict that isotope ratios such as 24Mg/25,26Mg are larger because of the contribution from low-metallicity supernovae. Using isotopic ratios it is possible to select stars that formed in a system with a low chemical enrichment efficiency such as the satellite galaxies that were accreted onto our own Milky Way Galaxy.

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