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arXiv 2104.05680astro-ph.GAastro-ph.SR
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初始质量函数对银河系化学富集的影响

On the effects of the Initial Mass Function on Galactic chemical enrichment

S. Goswami, A. Slemer, P. Marigo, A. Bressan, L. Silva, M. Spera, L. Boco, V. Grisoni, L. Pantoni, A. Lapi

摘要:

越来越多的证据表明,恒星初始质量函数(IMF)可以扩展到远超过经典Mi ~100,Msun极限,但这一假设对星系化学富集的影响仍有待澄清。我们的目标是解决这个问题,通过分析观察到的丰度薄和厚盘恒星在银河系中的化学演化模型,占非常大的恒星死亡的贡献对不稳定超新星。我们建立了一套新的化学产率从大质量和超大质量恒星到Mi ~ 350 Msun,结合风喷出物从我们的流体静力学恒星演化模型与爆炸喷出物从文献中提取。使用一个简单的化学演化代码,我们分析了采用不同的产量表的影响,通过比较预测对恒星在太阳附近的观测。经过几次测试,我们专注于[O/Fe]比,它最好地分离了两个银河系成分的化学模式。我们发现,与一个标准的国际货币基金组织,截断Mi ~ 100 Msun,我们可以重现各种观测的限制薄盘星,但相同的国际货币基金组织未能占厚盘星的[O/Fe]比。通过将IMF扩展到Mi = 350 Msun,并包括非常大质量恒星的化学喷出物,以风和对不稳定超新星explosions. Our的形式,我们的研究表明,PISN在塑造银河系厚盘的化学演化中发挥了重要作用。通过包括它们的化学产额,不仅可以更容易地再现α增强的水平,而且可以在[O/Fe] vs [Fe/H]图中再现厚盘星的观测斜率。最重要的是,超大质量恒星对星系化学富集的贡献可能非常重要,在化学演化模型中不应被忽视。

英文摘要:

There is mounting evidence that the stellar initial mass function (IMF) could extend much beyond the canonical Mi ~100, Msun limit, but the impact of such hypothesis on the chemical enrichment of galaxies still remains to be clarified. We aim to address this question by analysing the observed abundances of thin- and thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair-instability supernovae. We built new sets of chemical yields from massive and very massive stars up to Mi ~ 350 Msun, by combining the wind ejecta extracted from our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code we analyse the effects of adopting different yield tables by comparing predictions against observations of stars in the solar vicinity. After several tests, we focus on the [O/Fe] ratio which best separates the chemical patterns of the two Milky Way components. We find that with a standard IMF, truncated at Mi ~ 100 Msun, we can reproduce various observational constraints for thin-disc stars, but the same IMF fails to account for the [O/Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi = 350 Msun and including the chemical ejecta of very massive stars, in the form of winds and pair-instability supernova explosions.Our study indicates that PISN played a significant role in shaping the chemical evolution of the Milky Way thick disc. By including their chemical yields it is easier to reproduce not only the level of the alpha-enhancement but also the observed slope of thick-disc stars in the [O/Fe] vs [Fe/H] diagram. The bottom line is that the contribution of very massive stars to the chemical enrichment of galaxies is potentially quite important and should not be neglected in chemical evolution models.

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