NGC 362: another globular cluster with a split red giant branch-猫眼课题宝

DOI：

10.1051/0004-6361/201321905

发表时间：

2013-07

期刊：

Astronomy and Astrophysics

影响因子：

6.5

通讯作者：

中科院分区：

物理与天体物理2区

文献类型：

作者：

E. Carretta;A. Bragaglia;R. Gratton;S. Lucatello;V. D’Orazi;M. Bellazzini;G. Catanzaro;F. Leone;Y. Momany;A. O. A. D. Bologna-A.-O.-A.-D.-Bologna-102401858;I. Padova;D. Physics;Astronomy;M. Univ.;M. C. F. Astrophysics;Inaf - Catania;Dip. Fisica e Astr.;U. Catania;Eső

我们获得了球状星系团(GC)NGC362中第一代和第二代红巨星(RGB)的火焰长颈鹿+UVES光谱，并用它们得出了92颗恒星的21个原子物种的丰度。被测元素包括质子俘获(O、Na、Mg、Al、Si)、α俘获(Ca、Ti)、铁峰(Sc、V、Mn、Co、Ni、Cu)和中子俘获元素(Y、Zr、Ba、La、Ce、ND、Eu、Dy)。这一分析与本系列以前的论文中对20个GC的分析完全一致。NGC362中的恒星似乎沿着Na-O反关联被分成两个离散的群，在[O/Na]∼0dex处有一个间隙。富纳、二代明星呈现出更加集中的趋势，尽管信心水平并不是很高。与金属丰度相似但水平分支类型不同、总质量低得多的经典第二参数双星NGC288相比，NGC362恒星中的质子俘获过程似乎更加极端，这证实了先前的分析。我们发现存在一个二级RGB序列，它比RGB的大部分更红。初步估计，这一序列约占RGB恒星的6%。我们的光谱数据和文献测光表明，这个序列几乎完全由富Ba的巨星组成，并且可能像在其他星系团中发现的那样，富含所有S过程元素。在这方面，NGC 362加入了先前研究的GC，如NGC 1851、NGC 6656(M22)和NGC7089(M2)。

We obtained FLAMES GIRAFFE+UVES spectra for both first- and second-generation red giant branch (RGB) stars in the globular cluster (GC) NGC 362 and used them to derive abundances of 21 atomic species for a sample of 92 stars. The surveyed elements include proton-capture (O, Na, Mg, Al, Si), α-capture (Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr, Ba, La, Ce, Nd, Eu, Dy). The analysis is fully consistent with that presented for twenty GCs in previous papers of this series. Stars in NGC 362 seem to be clustered into two discrete groups along the Na-O anti-correlation with a gap at [O/Na] ∼ 0 dex. Na-rich, second generation stars show a trend to be more centrally concentrated, although the level of confidence is not very high. When compared to the classical second-parameter twin NGC 288 with similar metallicity but different horizontal branch type and a much lower total mass, the proton-capture processing in stars of NGC 362 seems to be more extreme, confirming previous analysis. We discovered the presence of a secondary RGB sequence, which is redder than the bulk of the RGB. A preliminary estimate shows that this sequence comprises about 6% of RGB stars. Our spectroscopic data and literature photometry indicate that this sequence is populated almost exclusively by giants rich in Ba and is probably rich in all s-process elements, as found in other clusters. In this regard, NGC 362 joins previously studied GCs like NGC 1851, NGC 6656 (M 22), and NGC 7089 (M 2).

NGC 362: another globular cluster with a split red giant branch

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