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arXiv 1302.4375astro-ph.SR
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大质量球状星团NGC 2419中多星群的深uVI LBT测光证据

Evidence for multiple populations in the massive globular cluster NGC 2419 from deep uVI LBT photometry

G. Beccari, M. Bellazzini, C. Lardo, A. Bragaglia, E. Carretta, E. Dalessandro, A. Mucciarelli, E. Pancino

备注：
13 pages, 12 figure, accepted for publication on MNRAS
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摘要：

我们提出了精确的宽视场uVI测光的远程和大规模的银河系球状星团NGC 2419，旨在寻找u-V的颜色沿红巨星分支（RGB），通常被解释为测光签名的存在下，多个人口的球状星团。对19.8<V<22.0等的RGB星，我们发现：（a）RGB脊线的u-V，u-I和V-I扩散明显大于观测误差所预期的，并通过大量的人造星实验精确地量化;（b）u-V和u-I的本征色扩散大于V-I，（c）在u-V和u-I中，位于RGB脊线蓝色处的恒星比位于该线红色处的恒星明显更集中于星团中心。所有上述观测事实都可以在这样一种情况下得到解释，即相当大一部分星团恒星属于第二代氦含量丰富的恒星。最后，我们发现[Mg/Fe]<0.0的明亮RGB星（17.5<V<19.0）优先位于星团RGB的红色一侧，而[Mg/Fe]>0.0的明亮RGB星优先位于星团RGB的蓝色一侧。

英文摘要：

We present accurate wide-field uVI photometry of the remote and massive Galactic globular cluster NGC 2419, aimed at searching for the u-V color spread along the Red Giant Branch (RGB) that is generally interpreted as the photometric signature of the presence of multiple populations in globular clusters. Focusing on the RGB stars in the magnitude range 19.8<V<22.0, we find that (a) the u-V, u-I and the V-I spreads about the RGB ridge line are significantly larger than that expected from observational errors, accurately quantified by means of extensive artificial stars experiments, (b) the intrinsic color spread in u-V and u-I are larger than in V-I, (c) the stars lying to the blue of the RGB ridge line in u-V and u-I are significantly more concentrated toward the cluster center than those lying to the red of that line. All the above observational facts can be interpreted in a scenario where a sizable fraction of cluster stars belong to a second generation heavily enriched in Helium. Finally we find that bright RGB stars (17.5<V<19.0) having [Mg/Fe]<0.0 lie preferentially on the red side of the cluster RGB, while those having [Mg/Fe]>0.0 lie preferentially on the blue side.

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