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arXiv 0811.3179astro-ph
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来自红超巨星大气层的银河系中心化学丰度

The chemical abundances in the Galactic Centre from the atmospheres of Red Supergiants

Ben Davies, Livia Origlia, Rolf-Peter Kudritzki, Don F. Figer, R. Michael Rich, Francisco Najarro

备注：
23 pages, 5 figs. Accepted for publication in ApJ
发表信息：
Astrophys.J.694:46-55,2009
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摘要：

银河系中心（GC）最近经历了高度的恒星形成活动，这可以从目前居住在那里的大量大质量恒星中得到证明。GC中化学元素的相对丰度可以提供对这种活动起源的见解。本文给出了两颗红超巨星（IRS~7和VR~5-7）的高分辨率$H$带光谱，结合光谱合成，我们得到了Fe和C以及其它$α$ -元素Ca、Si、Mg、Ti和O的丰度。结果表明，VR~5-7的碳亏损与RSG演化模型的预测相一致，而IRS~7大气中碳和氧的严重亏损则可能是由于快速的初始旋转和/或质量损失增强而导致的深层混合。结果表明，每颗恒星的{ \it电流}表面Fe/H含量都略高于太阳。然而，与演化模型的比较表明，{ \it初始}的Fe/H比可能更接近太阳系，并且由于恒星表面的H耗尽而变得更高。总体而言，我们发现$α$ /铁的比率为这两颗恒星是一致的薄银河系盘。这些结果与GC的其他化学研究一致，因为目前可以确定丰度的精度。我们认为，GC的丰度是一致的，在这种情况下，最近的恒星形成活动的GC是由材料从内部磁盘，或从风的恒星在内部膨胀的酒吧-没有必要调用头重脚轻的恒星初始质量函数来解释异常丰度比。

英文摘要：

The Galactic Centre (GC) has experienced a high degree of recent star-forming activity, as evidenced by the large number of massive stars currently residing there. The relative abundances of chemical elements in the GC may provide insights into the origins of this activity. Here, we present high-resolution $H$-band spectra of two Red Supergiants in the GC (IRS~7 and VR~5-7), and in combination with spectral synthesis we derive abundances for Fe and C, as well as other $α$-elements Ca, Si, Mg Ti and O. We find that the C-depletion in VR~5-7 is consistent with the predictions of evolutionary models of RSGs, while the heavy depletion of C and O in IRS~7's atmosphere is indicative of deep mixing, possibly due to fast initial rotation and/or enhanced mass-loss. Our results indicate that the {\it current} surface Fe/H content of each star is slightly above Solar. However, comparisons to evolutionary models indicate that the {\it initial} Fe/H ratio was likely closer to Solar, and has been driven higher by H-depletion at the stars' surface. Overall, we find $α$/Fe ratios for both stars which are consistent with the thin Galactic disk. These results are consistent with other chemical studies of the GC, given the precision to which abundances can currently be determined. We argue that the GC abundances are consistent with a scenario in which the recent star-forming activity in the GC was fuelled by either material travelling down the Bar from the inner disk, or from the winds of stars in the inner Bulge -- with no need to invoke top-heavy stellar Initial Mass Functions to explain anomalous abundance ratios.

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