Planetary nebulae abundances and stellar evolution II
Planetary nebulae abundances and stellar evolution II
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行星状星云丰度和恒星演化 II
DOI：
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发表时间：
2006
期刊：
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通讯作者：
J. Bernard
中科院分区：
文献类型：
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作者：
S. Pottasch;J. Bernard
上下文。近年来，对行星状星云的中、远红外光谱进行了分析，得到了更精确的丰度。可以预期，这些更丰富的丰度会使我们更好地理解这些天体的演化。目标。将观测到的行星状星云的丰度与Karakas（2003年，论文，墨尔本莫纳什大学）模型预测的丰度进行比较，以预测所使用的各种海王星星云的前身质量。PNe的形貌也包括在比较中。由于中心恒星在演化过程中扮演着重要的角色，人们期望通过这种比较可以获得更多关于它们的信息。方法。首先讨论了氮/氧比与氦/氢比的关系。通过与Karakas模型的比较，可以找到每个星云的前身质量。然后用两种方法确定中心恒星的当前光度：一是通过计算中心恒星的有效温度和半径，二是通过计算氢和氦谱线的星云光度。光度也是初始质量的函数，这样就可以比较这两个初始质量的值。结果。7个双极星云中有6个可以被确定为大质量恒星（4 - 6 μ M）的后代，而第7个则是模糊的。大多数椭圆型海王星星云的中心恒星都是由低初始质量恒星演化而来的，尽管有一些需要注意的地方需要讨论。没有观测证据表明碳氧比高的中心恒星质量更高。与Karakas模型的丰度比较所提供的证据与所比较的HR图是一致的。在这个讨论的过程中，它显示了如何将“光学薄”的星云与那些“光学厚”的星云分开。
Context. In recent years mid- and far infrared spectra of planetary nebulae have been analysed and lead to more accurate abundances. It may be expected that these better abundances lead to a better understanding of the evolution of these objects. Aims. The observed abundances in planetary nebulae are compared tothose predicted by the models of Karakas (2003, Thesis, Monash Univ. Melbourne) in order to predict the progenitor masses of the various PNe used. The morphology of the PNe is included in the comparison. Since the central stars play an important role in the evolution, it is expected that this comparison will yield additional information about them. Methods. First the nitrogen/oxygen ratio is discussed with relation to the helium/hydrogen ratio. The progenitor mass for each PNe can be found by a comparison with the models of Karakas. Then the present luminosity of the central stars is determined in two ways: first by computing the central star effective temperature and radius, and second by computing the nebular luminosity from the hydrogen and helium lines. This luminosity is also a function of the initial mass so that these two values of initial mass can be compared. Results. Six of the seven bipolar nebulae can be identified as descendants of high mass stars (4−6 M� ) while the seventh is ambiguous. Most of the elliptical PNe have central stars which descend from low initial mass stars, although there are a few caveats which are discussed. There is no observational evidence for a higher mass for central stars which have a high carbon/oxygen ratio. The evidence provided by the abundance comparison with the models of Karakas is consistent with the HR diagram to which it is compared. In the course of this discussion it is shown how “optically thin” nebulae can be separated from those which are “optically thick”.