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arXiv 0812.0854astro-ph
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根据疏散星团高分辨光谱研究银河系金属丰度梯度的演化

The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters

Laura Magrini, Paola Sestito, Sofia Randich, Daniele Galli

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16 pages, 18 figures, A&A accepted
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摘要：

疏散星团为研究银河系中几种元素的径向金属丰度梯度的时间演化提供了一种独特的可能性，因为它们在年龄和银心距离上跨越很大的间隔，而且这两个量都可以比场星更精确地推导出来。我们重新解决银河系金属丰度梯度和它的时间演化的问题，通过比较的经验梯度跟踪的一个样本的45个疏散星团与银河系的化学演化模型。与以前类似的研究不同，我们从文献中只收集了来自高分辨率光谱的丰度。这些星团的距离为$7 < RGC<22$ kpc，年龄从$\sim 30$ Myr到11 Gyr。我们还考虑了$α$元素Si、Ca、Ti和铁峰元素Cr和Ni。铁峰和$α$元素的数据表明，R_GC<12 $ kpc and a plateau at larger radii. The time evolution of the metallicity distribution is characterized by a uniform increase of the metallicity at all radii, preserving the shape of the gradient, with marginal evidence for a flattening of the gradient with time in the radial range 7-12 kpc. Our model is able to reproduce the main features of the metallicity gradient and its evolution with an infall law exponentially decreasing with radius and with a collapse time scale of the order of 8 Gyr at the solar radius. This results in a rapid collapse in the inner regions, i.e. $ R_{\rm GC} \lesssim 12$ kpc的金属丰度梯度很陡（我们认为这与晕坍缩形成盘的早期阶段有关），并且外部区域每单位面积的物质以恒定的速率随时间缓慢流入。

英文摘要：

Open clusters offer a unique possibility to study the time evolution of the radial metallicity gradients of several elements in our Galaxy, because they span large intervals in age and Galactocentric distance, and both quantities can be more accurately derived than for field stars. We re-address the issue of the Galactic metallicity gradient and its time evolution by comparing the empirical gradients traced by a sample of 45 open clusters with a chemical evolution model of the Galaxy. At variance with previous similar studies, we have collected from the literature only abundances derived from high--resolution spectra. The clusters have distances $7 < RGC<22$ kpc and ages from $\sim 30$ Myr to 11 Gyr. We also consider the $α$-elements Si, Ca, Ti, and the iron-peak elements Cr and Ni. The data for iron-peak and $α$-elements indicate a steep metallicity gradient for R_GC<12$ kpc and a plateau at larger radii. The time evolution of the metallicity distribution is characterized by a uniform increase of the metallicity at all radii, preserving the shape of the gradient, with marginal evidence for a flattening of the gradient with time in the radial range 7-12 kpc. Our model is able to reproduce the main features of the metallicity gradient and its evolution with an infall law exponentially decreasing with radius and with a collapse time scale of the order of 8 Gyr at the solar radius. This results in a rapid collapse in the inner regions, i.e. $R_{\rm GC}\lesssim 12$ kpc (that we associate with an early phase of disk formation from the collapse of the halo) and in a slow inflow of material per unit area in the outer regions at a constant rate with time.

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