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arXiv 0902.1833astro-ph.SRastro-ph.GA
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银河系晚型O型矮星的分析：弱风问题的更多约束

Analysis of Galactic late-type O dwarfs: more constraints on the weak wind problem

W. L. F. Marcolino, J. -C. Bouret, F. Martins, D. J. Hillier, T. Lanz, C. Escolano

备注：
A&A, accepted
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摘要：

为了解决弱风问题，我们研究了五颗晚型O型矮星的恒星和风性质。采用TLUSTY模式网格计算恒星参数，采用CMFGEN程序计算风参数。我们发现，光谱主要有光球起源。在CIV 1549中可以看到微弱的风信号，从那里获得的质量损失率与之前CMFGEN关于O 8 -9V恒星的结果一致。在这些质量损失率和理论预测值之间发现了大约2个数量级的差异（Mdot（Vink）），证实了在log L/Lsun < 5.2时修正的风动量-光度关系的崩溃或变陡。我们估计了样本恒星的碳丰度，并得出结论，其不确定性不会导致弱风问题。使用不同离子的谱线，即PV 1118，28、CIII 1176、NV 1239，43、Si IV 1394，03和NIV 1718，确定了所有物体的Mdot上限。所有得到的值也与理论预测不一致，支持弱风的现实。与CIV 1549一起，NV 1239，43的使用导致最低的质量损失率：上限表明Mdot必须小于约-1.0 dex Mdot（Vink）。关于其它转变，上限仍然指向低速率：Mdot必须小于约$(-0.5 \pm 0.2)$ dex Mdot（Vink）。我们研究了不同质量损失率的H α线的行为。我们还探索了用Mdot（Vink）拟合观察到的光谱的方法。通过使用大量的X射线，我们证实了很少有风排放发生，就像在弱风中一样。然而，不得不使用不切实际的X射线光度（log Lx/Lbol > -3.5）（略）。

英文摘要：

We have investigated the stellar and wind properties of a sample of five late-type O dwarfs in order to address the weak wind problem. A grid of TLUSTY models was used to obtain the stellar parameters, and the wind parameters were determined by using the CMFGEN code. We found that the spectra have mainly a photospheric origin. A weak wind signature is seen in CIV 1549, from where mass-loss rates consistent with previous CMFGEN results regarding O8-9V stars were obtained. A discrepancy of roughly 2 orders of magnitude is found between these mass-loss rates and the values predicted by theory (Mdot(Vink)), confirming a breakdown or a steepening of the modified wind momentum-luminosity relation at log L/Lsun < 5.2. We have estimated the carbon abundance for the stars of our sample and concluded that its uncertainty cannot cause the weak wind problem. Upper limits on Mdot were established for all objects using lines of different ions, namely, PV 1118,28, CIII 1176, NV 1239,43, Si IV 1394,03, and NIV 1718. All the values obtained are also in disagreement with theoretical predictions, bringing support to the reality of weak winds. Together with CIV 1549, the use of NV 1239,43 results in the lowest mass-loss rates: the upper limits indicate that Mdot must be less than about -1.0 dex Mdot(Vink). Regarding the other transitions, the upper limits still point to low rates: Mdot must be less than about $(-0.5 \pm 0.2)$ dex Mdot(Vink). We have studied the behavior of the Halpha line with different mass-loss rates. We have also explored ways to fit the observed spectra with Mdot(Vink). By using large amounts of X-rays, we verified that few wind emissions take place, as in weak winds. However, unrealistic X-rays luminosities had to be used (log Lx/Lbol > -3.5) (abridged).

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