忽略热星风的多孔性会导致低估质量损失率
Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
摘要：
背景：质量损失率是大质量恒星的一个关键参数。光谱分析和质量损失的测定需要适当的恒星大气模型。目前的模型只能在光学薄的小尺度结构的近似中解释恒星风的不均匀性。这种对"微聚集“的处理导致经验质量损失率降低两倍或更多。目的：星风团在谱线上可以是光学厚的。我们调查如何“大聚集”的影响经验的质量损失率。研究方法：波茨坦Wolf-Rayet（PoWR）模式大气代码在“形式积分”中被推广到不一定光学薄的团块。结果：光学厚团块降低有效不透明度。这对出射光谱有明显的影响。我们对O型超巨星zeta Puppis的建模表明，光学上薄的H-α线不受风孔隙度的影响，但当考虑到宏聚团时，PV共振双重线变得显着较弱。共振线和重组线诊断之间的差异，可以完全解决与大团簇建模没有向下修正的质量损失率。结论：从光学薄发射推断的质量损失率，如O型星中的H-α线，不受大团块的影响。然而，由于孔隙效应，光学粗线的强度降低。因此，在恒星风模拟中忽略孔隙度会导致低估经验质量损失率。
英文摘要：
Context: The mass-loss rate is a key parameter of massive stars. Adequate stellar atmosphere models are required for spectral analyses and mass-loss determinations. Present models can only account for the inhomogeneity of stellar winds in the approximation of small-scale structures that are optically thin. This treatment of ``microclumping'' has led to reducing empirical mass-loss rates by factors of two and more. Aims: Stellar wind clumps can be optically thick in spectral lines. We investigate how this ``macroclumping'' impacts on empirical mass-loss rates. Methods: The Potsdam Wolf-Rayet (PoWR) model atmosphere code is generalized in the ``formal integral'' to account for clumps that are not necessarily optically thin. Results: Optically thick clumps reduce the effective opacity. This has a pronounced effect on the emergent spectrum. Our modeling for the O-type supergiant zeta Puppis reveals that the optically thin H-alpha line is not affected by wind porosity, but that the PV resonance doublet becomes significantly weaker when macroclumping is taken into account. The reported discrepancies between resonance-line and recombination-line diagnostics can be resolved entirely with the macroclumping modeling without downward revision of the mass-loss rate. Conclusions: Mass-loss rates inferred from optically thin emission, such as the H-alpha line in O stars, are not influenced by macroclumping. The strength of optically thick lines, however, is reduced because of the porosity effects. Therefore, neglecting the porosity in stellar wind modeling can lead to underestimating empirical mass-loss rates.
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