The Primordial Helium Abundance: Toward Understanding and Removing the Cosmic Scatter in the dY/dZ Relation
The Primordial Helium Abundance: Toward Understanding and Removing the Cosmic Scatter in the dY/dZ Relation
复制标题
原始氦丰度：理解和消除 dY/dZ 关系中的宇宙散射
DOI：
10.1086/308984
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
P. Martin
中科院分区：
文献类型：
--
作者：
D. Ballantyne;G. Ferland;P. Martin
我们目前的结果从光电离模型的低金属氢II区。这些星云构成了测量原始氦丰度的基础。我们的模型表明，对于有效温度大于40，000 K的恒星激发的星云，氦电离校正因子（ICF）是不可忽略的。此外，我们发现，当有效温度上升到45,000 K以上，ICF可以显着负。这个结果与恒星大气的选择无关。然而，如果一个H II区的[O III] λ5007/[O I] λ6300比值大于300，那么我们的模型表明，不管它的金属丰度如何，它的ICF都小得可以忽略。使用[O III] λ5007/Hβ比率发现了类似的但依赖于金属性的结果。这两个结果可以用来作为选择标准，以消除潜在的不可忽略的ICF星云。使用我们的金属性独立的标准上的数据的Izotov和Thuan的结果在一个20%的最佳拟合Y-Z线的均方根分散减少。拟合选定的数据的结果在原始氦丰度的值略有增加。
We present results from photoionization models of low-metallicity H II regions. These nebulae form the basis for measuring the primordial helium abundance. Our models show that the helium ionization correction factor (ICF) can be nonnegligible for nebulae excited by stars with effective temperatures larger than 40,000 K. Furthermore, we find that when the effective temperature rises to above 45,000 K, the ICF can be significantly negative. This result is independent of the choice of stellar atmosphere. However, if an H II region has an [O III] λ5007/[O I] λ6300 ratio greater than 300, then our models show that, regardless of its metallicity, it will have a negligibly small ICF. A similar, but metallicity-dependent, result was found using the [O III] λ5007/Hβ ratio. These two results can be used as selection criteria to remove nebulae with potentially nonnegligible ICFs. Use of our metallicity-independent criterion on the data of Izotov & Thuan results in a 20% reduction of the rms scatter about the best-fit Y-Z line. A fit to the selected data results in a slight increase of the value of the primordial helium abundance.