Constraints on the Evolution of Massive Stars through Spectral Analysis. I. The WC5 Star HD 165763
Constraints on the Evolution of Massive Stars through Spectral Analysis. I. The WC5 Star HD 165763
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通过光谱分析限制大质量恒星的演化。
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发表时间：
1999
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通讯作者：
Douglas L. Miller
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作者：
D. Hillier;Douglas L. Miller
使用一个显着修订的非LTE辐射传输代码，允许由He，C，O，Si和Fe的线覆盖的影响，我们已经进行了详细的分析银河系沃尔夫-拉叶（W-R）星星HD 165763（WR 111，WC 5）。标准的W-R模型总是高估电子散射翼的强度，特别是在强线上，所以我们考虑了风既均匀又聚集的模型。HD 165763的恒星参数推导结果如下：HD 165763的恒星参数推导结果与先前的分析结果有显著差异。结果表明，光度值增大了2倍，核半径也减小了，这与恒星演化计算的结果吻合较好。这两种变化都可以归因于行覆盖的影响。推导出的C/He丰度与早期的计算结果相似，而O/He丰度以前没有确定过。所观察到的铁光谱，主要是由于Fe V和Fe VI，很好地再现使用太阳能铁的质量分数，虽然至少有一个因素的变化约2这个值不能被排除。特别是，该模型自然地产生以1470 nm为中心的Fe V发射特征和较短波长的复杂Fe发射/吸收光谱。此外，铁强烈修改线的强度和轮廓形状短的1800欧姆，必须考虑到，如果我们要成功地模拟这个区域。向HD 165763的变红并不遵循银河系的平均消光定律。我们确定的红化法律对HD 165763通过比较我们的模型连续水平的观测。为了同时匹配的紫外线，光学，特别是红外线通量，我们使用参数化的红化法的Cardelli，克莱顿，和马西斯与EB-V = 0.3和R = 4.5，其中R = AV/EB-V。根据观测和理论的建议，我们已经考虑了模型中的风仍在大半径加速。特别是，我们讨论的模型中，速度定律可以表征为β = 1 r <10 R *，但经历了一个显着的速度增加（~600 km s-1）超过10 R *。这些模型似乎稍微更好地拟合了谱线轮廓，但改进很小，而且很难衡量观测数据是否需要这样的速度定律。我们还不能确定W-R星的风是否是由辐射压力驱动的，因为我们忽略了模型离子中许多更高水平的铁，而且我们没有包括钴和镍等重要元素。然而，在W-R星的“风问题”是不那么严重，比以前假设的，如果发生结块。对于我们的聚集模型，单次散射极限仅超过10倍，而对于均匀风，该值为3倍。聚束现象似乎是解释W-R星明显的高质量损失率的关键，并且对于理解W-R风是如何甚至是否由辐射压力驱动非常重要。W-R质量损失率的降低对恒星演化计算具有重要意义。
Using a significantly revised non-LTE radiative transfer code that allows for the effects of line blanketing by He, C, O, Si, and Fe, we have performed a detailed analysis of the Galactic Wolf-Rayet (W-R) star HD 165763 (WR 111, WC5). Standard W-R models consistently overestimate the strength of the electron scattering wings, especially on strong lines, so we have considered models where the wind is both homogeneous and clumped. The deduced stellar parameters for HD 165763 are as follows: The stellar parameters deduced for HD 165763 are significantly different from earlier analyses. The deduced luminosity is a factor of 2 larger, and a smaller core radius is found. The smaller radius is in better agreement with expectations from stellar evolution calculations. Both of these changes can be attributed to the effects of line blanketing. The deduced C/He abundance is similar to earlier calculations, and the O/He abundance had not previously been determined. The observed iron spectrum, principally due to Fe V and Fe VI, is well reproduced using a solar iron mass fraction, although a variation of at least a factor of 2 about this value cannot be precluded. In particular, the models naturally produce the Fe V emission feature centered on 1470 Å and the complex Fe emission/absorption spectrum at shorter wavelengths. Also, Fe strongly modifies the line strengths and profile shapes shortward of 1800 Å and must be taken into account if we are to successfully model this region. The reddening toward HD 165763 does not follow the mean Galactic extinction law. We determine the reddening law toward HD 165763 by comparing our model continuum levels to observations. In order to simultaneously match the UV, optical, and particularly the infrared fluxes, we used the parameterized reddening law of Cardelli, Clayton, and Mathis with EB-V = 0.3 and R = 4.5, where R = AV/EB-V. Based on both observational and theoretical suggestions we have considered models in which the wind is still accelerating at large radii. In particular, we discuss models in which the velocity law can be characterized by β = 1 for r < 10R* but that undergo a substantial velocity increase (~600 km s-1) beyond 10R*. These models appear to give slightly better fits to the line profiles, but the improvements are small, and it is difficult to gauge whether observational data require such a velocity law. We cannot yet determine whether the winds of W-R stars are driven by radiation pressure, because we neglect many higher levels of iron in our model ions, and we do not include important elements such as cobalt and nickel. However, the "wind problem" in W-R stars is less severe than previously assumed if clumping occurs. For our clumped model, the single scattering limit is only exceeded by a factor of 10 compared to 3 times this value for a homogeneous wind. Clumping appears to be the key to explaining the apparent high mass-loss rates determined for W-R stars and is extremely important in understanding how or even whether W-R winds are driven by radiation pressure. A reduction in W-R mass-loss rates has important implications for stellar evolution calculations.