Modeling of PMS Ae/Fe stars using UV spectra
Modeling of PMS Ae/Fe stars using UV spectra
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使用 UV 光谱对 PMS Ae/Fe 星进行建模
DOI：
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发表时间：
2006
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通讯作者：
H. Djie
中科院分区：
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作者：
P. Blondel;P. Blondel;H. Djie
语境。基于目视观测的 PMS Ae/Fe 恒星的光谱分类可能会导致模糊的结论。目标。我们的目标是通过使用 UV 光谱对这些恒星进行分类来减少这些模糊性，因为 UV 中连续谱的上升对 A/F 型恒星的恒星光谱类型高度敏感。方法。我们根据三分量模型分析低分辨率紫外光谱，该模型由中心恒星的光谱、光学厚吸积盘的光谱以及吸积盘和恒星之间的边界层的光谱组成。圆盘分量是通过普朗克光谱的并置计算的，而其他两个分量则通过分类良好的标准恒星的低分辨率紫外光谱（取自 IUE 光谱图集）进行模拟。热边界层与晚 B 型超巨星的光谱有很强的相似性（见附录 A）。结果。我们对 37 颗 PMS Ae/Fe 星的低分辨率紫外光谱进行了建模。每个光谱匹配提供 8 个模型参数：光球层和边界层的光谱类型和光度等级、边界层的温度和宽度、盘倾角和星周消光。根据这些分析的结果，结合可用的理论 PMS 进化轨迹，我们可以估计它们的质量和年龄，并得出它们的质量吸积率。对于许多分析的 PMS 恒星，我们计算了相应的 SED，并将其与观测到的 SED 进行了比较。结论。所有恒星（β Pic 除外）都显示出吸积迹象，这会影响恒星光球层的光谱类型。以前，由于没有考虑边界层，这导致了 PMS 恒星分类的模糊性。我们提供的证据表明质量吸积率随着恒星质量的增加而增加，并且随着恒星年龄的增加而减少。
Context. Spectral classification of PMS Ae/Fe stars, based on visual observations, may lead to ambiguous conclusions. Aims. We aim to reduce these ambiguities by using UV spectra for the classification of these stars, because the rise of the continuum in the UV is highly sensitive to the stellar spectral type of A/F-type stars. Methods. We analyse the low-resolution UV spectra in terms of a 3-component model, that consists of spectra of a central star, of an optically-thick accretion disc, and of a boundary-layer between the disc and star. The disc-component was calculated as a juxtaposition of Planck spectra, while the 2 other components were simulated by the low-resolution UV spectra of well-classified standard stars (taken from the IUE spectral atlases). The hot boundary-layer shows strong similarities to the spectra of late-B type supergiants (see Appendix A). Results. We modeled the low-resolution UV spectra of 37 PMS Ae/Fe stars. Each spectral match provides 8 model parameters: spectral type and luminosity-class of photosphere and boundary-layer, temperature and width of the boundary-layer, disc-inclination and circumstellar extinction. From the results of these analyses, combined with available theoretical PMS evolutionary tracks, we could estimate their masses and ages and derive their mass-accretion rates. For a number of analysed PMS stars we calculated the corresponding SEDs and compared these with the observed SEDs. Conclusions. All stars (except β Pic) show indications of accretion, that affect the resulting spectral type of the stellar photosphere. Formerly this led to ambiguities in classificaton of PMS stars as the boundary-layer was not taken into consideration. We give evidence for an increase of the mass-accretion rate with stellar mass and for a decreases of this rate with stellar age.