arXiv 1612.030442016-12-09astro-ph.SR

主序星上大质量恒星的光谱演化

Spectroscopic evolution of massive stars on the main sequence

F. Martins, A. Palacios

备注：: 15 pages, 15 figures. Astronomy & Astrophysics accepted
DOI：: 10.1051/0004-6361/201629538

摘要：

我们提供了一个观察的观点，在赫茨伯格-罗素图的演化模型，在主序列。为此，我们使用代码STAREVOL计算了15 < M/Msun < 100的进化模型。随后，我们使用代码CMFGEN计算了沿演化轨迹特定点的大气模型。以这种方式获得的合成光谱被归类为观测数据。我们通过与观测到的各种恒星的光谱进行比较来测试我们的光谱分类。我们还将我们的结果与大量OB星的经验数据进行了比较。我们得到了进化轨迹上的光谱序列。在我们的计算中，最早的O星（O2-3.5）只出现在50 Msun以上。对于后来的光谱类型，存在类似的质量限制，但更低。光度等级V并不对应于整个主序。这只适用于15 Msun轨道。随着质量的增加，主序的大部分时间都在III类光度中度过。在50兆太阳以上，超巨星在核心氢燃烧结束之前出现。在80 Msun以上的零龄主序星上不会出现矮星。因此，HR图中V类光度的分布不能用来限制对流核心的大小。在HR图中，矮星和巨星的分布与用定量光谱分析的恒星位置吻合得很好。对于超巨星，在观测到I类光度比我们的预测稍早的意义上有一个微小的差异。这主要是由于风的密度影响光度级的诊断线。我们预测矮恒星的质量上限（~60 Msun），这与银河系中O2 V恒星的稀有性一致。我们的模型没有预测到具有WNh光谱类型的恒星。需要更强的风来产生这些物体的特征发射线。

英文摘要：

We provide an observational view of evolutionary models in the Hertzsprung--Russell diagram, on the main sequence. For that we computed evolutionary models with the code STAREVOL for 15 < M/Msun < 100. We subsequently calculated atmosphere models at specific points along the evolutionary tracks, using the code CMFGEN. Synthetic spectra obtained in this way were classified as if they were observational data. We tested our spectral classification by comparison to observed spectra of various stars. We also compared our results with empirical data of a large number of OB stars. We obtain spectroscopic sequences along evolutionary tracks. In our computations, the earliest O stars (O2-3.5) appear only above ~50 Msun. For later spectral types, a similar mass limit exists, but is lower. A luminosity class V does not correspond to the entire main sequence. This only holds for the 15 Msun track. As mass increases, a larger portion of the main sequence is spent in luminosity class III. Above 50 Msun, supergiants appear before the end of core-hydrogen burning. Dwarf stars do not occur on the zero-age main sequence above 80 Msun. Consequently, the distribution of luminosity class V in the HR diagram cannot be used to constrain the size of the convective core. The distribution of dwarfs and giants in the HR diagram agrees well with the location of stars analyzed by means of quantitative spectroscopy. For supergiants, there is a slight discrepancy in the sense that luminosity class I is observed slightly earlier than our predictions. This is mainly due to wind densities that affect the luminosity class diagnostic lines. We predict an upper mass limit for dwarf stars (~60 Msun) that is found consistent with the rarity of O2V stars in the Galaxy. Stars with WNh spectral type are not predicted by our models. Stronger winds are required to produce the characteristic emission lines of these objects.

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