标题： 详细分析四颗[WR]星的远紫外至光学波段特性 显示英文标题

标题： Detailed Far-UV to Optical Analysis of Four [WR] Stars

摘要： 我们对四个行星状星云的氢缺乏中心星进行了远紫外至光学波段的分析：BD+303639、NGC 40、NGC 5315 和 NGC 6905。 利用辐射转移代码 CMFGEN，我们为这些恒星确定了新的物理参数和化学丰度。 这些结果在 [WR] => PG 1159 演化过程中通过变换半径 (Rt)-温度图和赫罗图进行了分析。 在之前分析过的中心星中，NGC 5315 表现为一个异常对象。 它的温度（~76 kK）明显低于其他早期型 [WR] 星（~120-150 kK）。 根据我们对 NGC 5315 和 NGC 6905 的模型，尚不清楚早期型 [WR] 星是否具有比其他光谱类型更小的 C/He 质量比，正如文献所述。 对于 NGC 6905，我们发现 C/He 比值约为 0.8。 我们首次分析了这些恒星的 FUSE 光谱，并通过 P V 1118、1128 谱线跃迁在 BD+303639、NGC 40 和 NGC 5315 的光谱中识别出磷元素。 Fe、Si、P、S 和 Ne 的丰度在前一演化阶段发生的核合成背景下进行了分析。 我们在 BD+303639 和 NGC 5315 中发现了铁缺乏的证据，并通过 Si IV 线拟合得出 BD+303639 和 NGC 40 的硅丰度接近太阳值。 对于磷元素，在 NGC 5315 模型中偏好超太阳丰度，而在其他恒星中无法排除太阳丰度。 至于硫元素，由于观测光谱中没有明显的谱线，我们估计了其丰度的上限。 我们发现 BD+303639 中氖元素过量，而在其他恒星中氖元素较弱或无法检测，也估计了其丰度的上限。 我们的结果与理论预测一致，表明 [WR] 恒星作为 AGB 和后 AGB 阶段核合成计算的测试平台具有实用性。 （摘要） 显示英文摘要

摘要： We present far-UV to optical analyses of four hydrogen deficient central stars of planetary nebulae: BD+303639, NGC 40, NGC 5315 and NGC 6905. Using the radiative transfer code CMFGEN, we determined new physical parameters and chemical abundances for these stars. The results were analyzed in the context of the [WR] => PG 1159 evolution via the transformed radius(Rt)-temperature and HR diagrams. NGC 5315 showed itself as an odd object among the previously analyzed central stars. Its temperature (~76kK) is considerably lower than other early-type [WR] stars (~120-150kK). From our models for NGC 5315 and NGC 6905, it is unclear if early-type [WR] stars have smaller C/He mass ratios than other spectral classes, as claimed in the literature. A ratio of ~0.8 is found for NGC 6905. We analyzed FUSE spectra of these stars for the first time, and identified phosphorus in the spectra of BD+303639, NGC 40 and NGC 5315 through the transitions P V 1118,1128. The Fe, Si, P, S and Ne abundances were analyzed in the context of the nucleosynthesis occurring in previous evolutionary phases. We found evidence for Fe deficiency in BD +30 3639 and NGC 5315, and from fits to the Si IV lines we determined a solar Si abundance for BD+303639 and NGC 40. For phosphorus, an oversolar abundance in the NGC 5315 model was preferred, while in the other stars a solar phosphorus abundance cannot be discarded. Regarding sulfur, we estimated upper limits for its abundance, since no conspicuous lines can be seen in the observed spectra. We found that Ne is overabundant in BD +30 3639. In the other stars, Ne is weak or undetectable and upper limits for its abundance were estimated. Our results are in agreement with theoretical predictions and show the usefulness of [WR] stars as testbeds for nucleosynthesis calculations in the AGB and post-AGB phases.(abridged)