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arXiv 0901.2273astro-ph.SR
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M33行星状星云的数量及其金属丰度梯度：对星系遥远过去的观察

The planetary nebula population of M33 and its metallicity gradient: A look into the galaxy's distant past

Laura Magrini, Letizia Stanghellini, Eva Villaver

备注：
25 pages, 12 figures, ApJ submitted
发表信息：
Astrophys.J.696:729-740,2009
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摘要：

在MMT上用Hectospec多光纤光谱仪研究了M33的行星状星云（PN）。在本文中，我们提出了102 PNe的光谱，而等离子体诊断和化学丰度进行了必要的诊断线测量的93 PNe。大约有20%的PNe符合I型，其余的样本是古老星盘恒星星族的后代，主序星质量M<3 M ${_\odot}$，年龄t $>$ 0.3 Gyr。通过对M33盘PNe元素丰度的研究，我们推断：（1）O/H和Ne/H之间存在密切的相关关系，但不包括氧的析出;（2）$α$ -元素的平均丰度与\hii区一致，表明从PN祖细胞形成的时期到现在，M33在盘中的全球富集可以忽略不计;（3）M33盘的径向氧梯度的斜率为-0.031 $\pm$ 0.013 dex kpc $^{-1}$，在误差范围内与HII区的相应梯度一致。我们的观察似乎并不意味着M33盘上的金属丰度梯度随着时间的推移而变得相当平坦。我们还报告发现了一个具有沃尔夫-拉叶特特征的PN，PN 039，属于晚[WC]星

英文摘要：

The Planetary Nebula (PN) population of M33 is studied via multi-fiber spectroscopy with Hectospec at the MMT. In this paper we present the spectra of 102 PNe, whereas plasma diagnostic and chemical abundances were performed on the 93 PNe where the necessary diagnostic lines were measured. About 20% of the PNe are compatible with being Type I; the rest of the sample is the progeny of an old disk stellar population, with main sequence masses M<3M${_\odot}$ and ages t$>$0.3 Gyr. By studying the elemental abundances of the PNe in the M33 disk we were able to infer that: (1) there is a tight correlation between O/H and Ne/H, broadly excluding the evolution of oxygen; (2) the average abundances of the $α$-elements are consistent with those of \hii regions, indicating a negligible global enrichment in the disk of M33 from the epoch of the formation of the PN progenitors to the present time; (3) the radial oxygen gradient across the M33 disk has a slope of -0.031$\pm$0.013 dex kpc$^{-1}$, in agreement, within the errors, with the corresponding gradient derived from HII regions. Our observations do not seem to imply that the metallicity gradient across the M33 disk has flattened considerably with time. We report also the discovery of a PN with Wolf-Rayet features, PN039, belonging the class of late [WC] stars

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