Quantitative analysis of WC stars: constraints on neon abundances from ISO-SWS spectroscopy
Quantitative analysis of WC stars: constraints on neon abundances from ISO-SWS spectroscopy
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WC 星的定量分析：ISO-SWS 光谱对氖丰度的限制
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发表时间：
2000
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通讯作者：
K. A. Hucht
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作者：
L. Dessart;P. Crowther;D. Hillier;A. Willis;P. Morris;K. A. Hucht
使用 ISO-SWS 获得的中红外精细结构线，从四颗银河 WC 星 - gamma(2) Vel (WR 11, WC8+O7.5III)、HD 156385 (WR 90, WC7)、HD 192103 (WR 135, WC8) 和 WR 146 (WC5+O8) 中推导出氖丰度。每颗恒星的恒星参数均使用 Hillier & Miller 的非局域热力学平衡模型大气代码以及紫外 (IUE)、光学 (INT、AAT) 和红外 (UKIRT、ISO) 光谱得出。对于 gamma(2) Vel，我们采用了 De Marco 等人的最新结果，他们遵循了相同的方法。ISO-SWS 数据集揭示了我们每个目标中的 [Ne III] 15.5-mu m 线，而 [Ne II] 12.8 mu m、[S IV] 10.5 mu m 和 [S III] 18.7 mu m 仅在 gamma(2) Vel 中观察到。使用 Barlow 等人更新的方法。为了解释聚集风，我们通过数字推导出 Ne/He = (3-4) x 10(-3)，加上 gamma(2) Vel 的 S/He = 6 x 10(-5)。氖气高度丰富，使得 gamma(2) Vel 中的 Ne/S 比宇宙值高八倍。然而，观测到的 Ne/He 比率比当前大质量恒星演化模型的预测低 2 倍。不精确的质量损失和距离是导致 Barlow 等人发现的氖含量差异更大的原因。我们的 WC5-8 恒星样本在 T-* (= 55-71 kK) 中的范围很窄，在早期光谱类型下没有温度升高的趋势，这支持了 Koesterke 和 Hamann 的更大样本的早期结果。恒星光度范围为 100 000 至 500 000 L.，而 10(-5.1) 小于或等于 M/(M.yr(-1)) 小于或等于 10(-4.5) 采用聚集风，其中体积填充因子为 10%。在所有情况下，风力性能数字均小于 10，明显低于最近的估计。按数量计算，碳丰度范围为 0.08 小于或等于 C/He 小于或等于 0.25，而氧丰度仍然受到很少的限制。
Neon abundances are derived in four Galactic WC stars - gamma(2) Vel (WR 11, WC8+O7.5III), HD 156385 (WR 90, WC7), HD 192103 (WR 135, WC8) and WR 146 (WC5+O8) - using mid-infrared fine-structure lines obtained with ISO-SWS. Stellar parameters for each star are derived using the non-local thermodynamic equilibrium model atmospheric code of Hillier & Miller, together with ultraviolet (IUE), optical (INT, AAT) and infrared (UKIRT, ISO) spectroscopy. In the case of gamma(2) Vel, we adopt very recent results from De Marco et al., who followed an identical approach.ISO-SWS data sets reveal the [Ne III] 15.5-mu m line in each of our targets, while [Ne II] 12.8 mu m, [S IV] 10.5 mu m and [S III] 18.7 mu m are observed solely in gamma(2) Vel. Using a method updated from Barlow et al. to account for clumped winds, we derive Ne/He = (3-4) x 10(-3) by number, plus S/He = 6 x 10(-5) for gamma(2) Vel. Neon is highly enriched, such that Ne/S in gamma(2) Vel is eight times higher than cosmic values. However, observed Ne/He ratios are a factor of 2 lower than predictions of current evolutionary models of massive stars. An imprecise mass loss and distance were responsible for the much greater discrepancy in neon content identified by Barlow et al.Our sample of WC5-8 stars span a narrow range in T-* (=55-71 kK), with no trend towards higher temperature at earlier spectral type, supporting earlier results for a larger sample by Koesterke & Hamann. Stellar luminosities range from 100 000 to 500 000 L., while 10(-5.1) less than or equal to M/(M. yr(-1)) less than or equal to 10(-4.5) adopting clumped winds, in which volume filling factors are 10 per cent. In all cases, wind performance numbers are less than 10, significantly lower than recent estimates. Carbon abundances span 0.08 less than or equal to C/He less than or equal to 0.25 by number, while oxygen abundances remain poorly constrained.