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arXiv 0810.0205astro-ph
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造父变星的星系丰度梯度：关于10-12 kpc附近的铁丰度梯度

Galactic abundance gradients from Cepheids : On the iron abundance gradient around 10-12 kpc

B. Lemasle, P. Francois, A. Piersimoni, S. Pedicelli, G. Bono, C. D. Laney, F. Primas, M. Romaniello

备注：
5 tables, 8 figures, Accepted in A&A
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摘要：

内容：经典造父变星可以用来追踪银盘的化学演化，因为它们的距离可以非常精确地估计。目的：通过对位于外盘的33颗造父变星的均匀铁丰度测量以及基于近红外光度法的精确距离测定，将银河系铁梯度限制在10 kpc以上。研究方法：铁丰度是使用三种不同的观测仪器收集的高分辨率造父变星光谱确定的：ESPaDOnS@CFHT，Narval@TBL和FEROS@2.2 m ESO/MPG望远镜。造父变星的距离是使用近红外（J，H，K波段）周期光度关系和SAAO和2 MASS星表的数据估算的。结果如下：对整个数据集的最小二乘解表明，银河系圆盘中的铁梯度在5-17 kpc范围内呈现出-0.052+/-0.003 dex/kpc的斜率。然而，铁丰度在整个磁盘的变化似乎是更好地描述了一个线性制度内的太阳圈和平坦的梯度向外盘（超过10千秒差距）。在后一区域，铁梯度呈现较浅的斜率，即-0.012+/-0.014 dex/kpc。在外盘（10-12千秒差距），我们还发现造父变星的铁丰度增加。目前的证据表明，金属丰度的分布取决于银河中心经度。最后，目前的数据不支持铁梯度在银河系中心距离为10-12千秒差距的假设。结论：铁丰度作为银河系中心经度的函数的扩散的发生表明，线性径向梯度应谨慎对待，以约束整个磁盘的化学演化。

英文摘要：

Context: Classical Cepheids can be adopted to trace the chemical evolution of the Galactic disk since their distances can be estimated with very high accuracy. Aims: Homogeneous iron abundance measurements for 33 Galactic Cepheids located in the outer disk together with accurate distance determinations based on near-infrared photometry are adopted to constrain the Galactic iron gradient beyond 10 kpc. Methods: Iron abundances were determined using high resolution Cepheid spectra collected with three different observational instruments: ESPaDOnS@CFHT, Narval@TBL and FEROS@2.2m ESO/MPG telescope. Cepheid distances were estimated using near-infrared (J,H,K-band) period-luminosity relations and data from SAAO and the 2MASS catalog. Results: The least squares solution over the entire data set indicates that the iron gradient in the Galactic disk presents a slope of -0.052+/-0.003 dex/kpc in the 5-17 kpc range. However, the change of the iron abundance across the disk seems to be better described by a linear regime inside the solar circle and a flattening of the gradient toward the outer disk (beyond 10 kpc). In the latter region the iron gradient presents a shallower slope, i.e. -0.012+/-0.014 dex/kpc. In the outer disk (10-12 kpc) we also found that Cepheids present an increase in the spread in iron abundance. Current evidence indicates that the spread in metallicity depends on the Galactocentric longitude. Finally, current data do not support the hypothesis of a discontinuity in the iron gradient at Galactocentric distances of 10-12 kpc. Conclusions: The occurrence of a spread in iron abundance as a function of the Galactocentric longitude indicates that linear radial gradients should be cautiously treated to constrain the chemical evolution across the disk.

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