Properties of Galactic early-type O-supergiants - A combined FUV-UV and optical analysis
Properties of Galactic early-type O-supergiants - A combined FUV-UV and optical analysis
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银河系早期 O 型超巨星的特性——FUV-UV 和光学分析相结合
DOI：
10.1051/0004-6361/201118594
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发表时间：
2012
影响因子：
6.5
通讯作者：
A. Fullerton
中科院分区：
文献类型：
--
作者：
J. Bouret;D. Hillier;Thierry Lanz;A. Fullerton
我们的目标是限制早期和中谱型超巨星(从O4到O7.5)的性质和演化状态。这些恒星的质量损失率是O型恒星中最高的，并显示出明显的风廓线。使用非LTE WIND程序CMFGEN，同时分析了FUV-UV和光学光谱范围，以确定光球层的性质和风参数。我们得到了有效温度、光度、表面重力、表面丰度、质量损失率、风端风速和块状填充因子。根据年龄和质量，这些超级巨星定义了一个非常清晰的演化序列，从更年轻、质量更大的恒星到初始质量更低的年龄更大的恒星。O4超巨星围绕3Myr等时线聚集，质量大于60mSun，而O5到O7.5恒星的质量范围在50-40mSun之间，年龄为4+/-0.3myr。其表面化学成分是典型的演化O超巨星(富氮、贫碳和贫氧)。虽然观测到的碳和氮质量分数的范围与测量恒星质量的演化模型预期的范围一致，但随年龄变化的N/C比与该样本中最早的四颗(O4谱型)恒星的理论预测不一致。我们质疑这些恒星的旋转混合效率与年龄的关系，并提出可能需要另一种机制来解释观察到的丰度模式。用块状模型得到的质量损失率的范围是理论质量损失率的三倍。与小规模聚集相关的相应体积填充因子为0.05+/-0.02。研究发现，除了三颗恒星外，所有恒星都是从接近光球层开始聚集的，其中两颗恒星的自转速度很快。
We aim to constrain the properties and evolutionary status of early and mid-spectral type supergiants (from O4 to O7.5). These posses the highest mass-loss rates among the O stars, and exhibit conspicuous wind profiles. Using the non-LTE wind code CMFGEN, we simultaneously analyzed the FUV-UV and optical spectral range to determine the photospheric properties and wind parameters. We derived effective temperatures, luminosities, surface gravities, surface abundances, mass-loss rates, wind terminal velocities, and clumping filling factors. The supergiants define a very clear evolutionary sequence, in terms of ages and masses, from younger and more massive stars to older stars with lower initial masses. O4 supergiants cluster around the 3 Myr isochrone and are more massive than 60 Msun, while the O5 to O7.5 stars have masses in the range 50 - 40 Msun and are 4 +/- 0.3 Myr old. The surface chemical composition is typical of evolved O supergiants (nitrogen-rich, carbon- and oxygen-poor). While the observed ranges of carbon and nitrogen mass-fractions are compatible with those expected from evolutionary models for the measured stellar masses, the N/C ratios as a function of age are inconsistent with the theoretical predictions for the four earliest (O4 spectral type) stars of the sample. We question the efficiency of rotational mixing as a function of age for these stars and suggest that another mechanism may be needed to explain the observed abundance patterns. Mass-loss rates derived with clumped-models range within a factor of three of the theoretical mass-loss rates. The corresponding volume-filling factors associated with small-scale clumping are 0.05 +/- 0.02. Clumping is found to start close to the photosphere for all but three stars, two of which are fast rotators.
影响因子：
6.5
作者：
A. Pauldrach;D. Vanbeveren;D. Vanbeveren;T. Hoffmann
通讯作者：
A. Pauldrach;D. Vanbeveren;D. Vanbeveren;T. Hoffmann