Planetary nebulae and H ii regions in the spiral galaxy NGC 300 - Clues on the evolution of abundance gradients and on AGB nucleosynthesis
Planetary nebulae and H ii regions in the spiral galaxy NGC 300 - Clues on the evolution of abundance gradients and on AGB nucleosynthesis
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DOI：
10.1051/0004-6361/201220345
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发表时间：
2013-01
影响因子：
6.5
通讯作者：
G. Stasińska;M. Peña;F. Bresolin;Y. G. Tsamis
中科院分区：
文献类型：
--
作者：
G. Stasińska;M. Peña;F. Bresolin;Y. G. Tsamis
我们获得了邻近旋涡星系NGC 300中26个行星状星云（PNe）和9个致密H ii区的深谱，并与以前观测到的巨H ii区的深谱一起进行了分析。我们已经以一致的方式确定了所有这些物体的物理性质及其He，N，O，Ne，S和Ar丰度。我们发现，在全球范围内，紧凑的H ii区域的丰度比类似的巨型H ii区域，而PNe系统有较大的N/O比和类似的Ne/O和Ar/O比。我们证明了PNe中的氮增强不能仅仅是由于祖星的第二次疏浚，因为它们的初始质量约为2-2.5 M�。需要一个额外的混合过程，也许是由恒星旋转驱动的。关于径向丰度分布，PNe表现不同的H II区域：在星系的中心部分，其平均O/H丰度比为0.15德克斯小。它们在任何银河系中心半径的丰度分散度显着大于H ii区域所示，其中许多具有O/H值高于H ii区域在相同的银河系中心距离。这表明不仅氮，而且氧也受到PN祖细胞核合成的影响，其数量至少取决于恒星的旋转速度和其他参数。PNe区的O/H、Ne/ Ha和Ar/He丰度梯度明显小于H ii区。我们认为，这表明在NGC 300的金属丰度梯度在最后Gyr陡峭，而不是径向恒星运动的影响，虽然大的分散观察到这个结论只是试探性的。
We have obtained deep spectra of 26 planetary nebulae (PNe) and 9 compact H ii regions in the nearby spiral galaxy NGC 300, and analyzed them together with those of the giant H ii regions previously observed. We have determined the physical properties of all these objects and their He, N, O, Ne, S and Ar abundances in a consistent way. We find that, globally, compact H ii regions have abundance ratios similar to those of giant H ii regions, while PNe have systematically larger N/O ratios and similar Ne/ Oa nd Ar/O ratios. We demonstrate that the nitrogen enhancement in PNe cannot be only due to second dredge-up in the progenitor stars, since their initial masses are around 2–2.5 M� . An extra mixing process is required, perhaps driven by stellar rotation. Concerning the radial abundance distribution, PNe behave differently from H ii regions: in the central part of the galaxy their average O/H abundance ratio is 0.15 dex smaller. Their abundance dispersion at any galactocentric radius is significantly larger than that shown by H ii regions and many of them have O/H values higher than H ii regions at the same galactocentric distance. This suggests that not only nitrogen, but also oxygen is affected by nucleosynthesis in the PN progenitors, by an amount which depends at least on the stellar rotation velocity and possibly other parameters. The formal O/H, Ne/ Ha nd Ar/He abundance gradients from PNe are significantly shallower than those from H ii regions. We argue that this indicates a steepening of the metallicity gradient in NGC 300 during the last Gyr, rather than an effect of radial stellar motions, although the large observed dispersion makes this conclusion only tentative.