Combined stellar structure and atmosphere models for massive stars III. Spectral evolution and revised ionizing fluxes of O3-B0 stars
Combined stellar structure and atmosphere models for massive stars III. Spectral evolution and revised ionizing fluxes of O3-B0 stars
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大质量恒星的恒星结构和大气组合模型 III。
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
A. D. Koter
中科院分区：
文献类型：
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作者：
D. Schaerer;A. D. Koter
我们提供了一套广泛的理论光谱能量分布的大质量恒星来自我们的组合恒星结构和大气模型。计算涵盖了初始质量Mi = 2.0 {1.20 M，对应于所有光度类的O_3 {B_0星的整体序列演化。我们预测详细的线覆盖的紫外光谱沿着主要序列的演变。主要结果是系统的研究电离通量覆盖整个参数空间的O和早期B星。我们证明了同时考虑非LTE效应、线覆盖和恒星风的重要性，以获得对这些恒星光谱的精确描述，这些恒星的光谱短于莱曼极限。从我们的光谱的主要结果如下：在He II连续的通量增加了2至3（3至6）个数量级的预测相比，从平面平行非LTE（LTE）模型大气。这再次证实了Gabler等人（1989）的工作。已知He i连续谱中的通量由于非He i效应而增加。然而，我们发现，它也受到风效应的影响，正如Najarroet al.（1996）和Schaerer et al.（1996 b）先前发现的那样。质量外流和谱线覆盖的综合效应导致He i连续谱中能量分布更加平坦，这与Sellmaier等人（1996）在更宽的恒星参数范围内的结果一致。莱曼连续谱中的通量也会由于线覆盖和恒星风的存在而发生变化，尽管变化的程度比高能时的光谱要小。根据Vacca等人（1996）最近的温度和重力校准，我们得到了O3到B 0星的修正电离通量。发现莱曼连续谱光子的总数略低于以前的推导。在大多数情况下，差异小于20%。由于He i连续谱中的通量增加，He i与H连续谱的硬度比增加了1.6至2.5，这取决于光谱类型和光度类别。根据最近的EUV和X射线观测，对当前模型假设（包括我们自己的）的批判性讨论表明，对于光谱类型晚于大约B 0的恒星，其恒星风相对较弱，电离通量的可靠预测尚不可能。我们确定了最有可能的物理原因，这种nding。
We provide an extensive set of theoretical spectral energy distributions of massive stars derived from our com- bined stellar structure and atmosphere models". The calcula- tionscovertheentiremainsequenceevolutionforinitialmasses Mi =2 0 {1 20 M, corresponding to O3{B0 stars of all lumi- nosity classes. We predict detailed line blanketed UV spectra along the main sequence evolution. The major result is a systematic study of ionizing fluxes covering the entire parameter space of O and early B stars. We demonstrate the importance of accounting simultaneously for non{LTE effects, line blanketing and stellar winds to obtain an accurate description of the spectra of these stars shortward of the Lyman limit. The main results from our spectra are the following: The flux in the He ii continuum is increased by 2 to 3 (3 to 6) orders of magnitudes compared to predictions from plane parallel non{LTE (LTE) model atmospheres. This re- conrms the work of Gabler et al. (1989). The flux in the He i continuum is known to be increased due non{LTE effects. However, we nd that it is also influ- encedbywindeffectsaswaspreviouslyfoundbyNajarroet al. (1996) and Schaerer et al. (1996b). The combined effect of a mass outflow and line blanketing leads to a flatter en- ergy distribution in the He i continuum, which conrms the results of Sellmaier et al. (1996) for a wider range of stellar parameters. The flux in the Lyman continuum is also modied due to line blanketing and the presence of a stellar winds, although to a lesser degree than the spectrum at higher energies. We derive revised ionizing fluxes for O3 to B0 stars based on the recent temperature and gravity calibrations of Vacca et al. (1996). The total number of Lyman continuum photons is found to be slightly lower than previous derivations. For most cases the differences are less than 20 %. Due to the increased flux in the He i continuum the hardness ratio of the He i to H continuum is increased by 1.6 to 2.5 depending on spectral type and luminosity class. In the view of recent EUV and X-ray observations, a critical discussion of current model assumptions (including our own) shows that for stars of spectral types later than approximately B0, which have relatively weak stellar winds, reliable predic- tions of ionizing fluxes are not yet possible. We identify the most likely physical reasons for this nding.