Interpretation of the intrinsic polarizations of early-type emission-line stars
Interpretation of the intrinsic polarizations of early-type emission-line stars
复制标题
早期型发射线恒星本征偏振的解释
DOI：
10.1093/mnras/186.2.265
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发表时间：
1979
影响因子：
4.8
通讯作者：
I. McLean
中科院分区：
文献类型：
--
作者：
I. McLean
模型，如卡普斯，Coyne和戴克解释连续线性偏振在Be星的散射和吸收分离的盘状信封电离氢进行了更深入的研究。偏振的时间依赖性和相对波长依赖性都可以用于区分轴对称和非轴对称包络结构。后者的结构是特别相关的早期类型的情况下，质量损失的二元系统和适当的偏振可以产生的轨道倾角。本文证明了全对称的准光学薄Be星包络在连续谱中具有近似相同形式的偏振波长依赖性，并且这种依赖性是由包络的平均性质所控制的。偏振结构的多普勒加宽的发射线和壳吸收功能和/或P Cygni的配置文件发生在这些拱壳可以归因于线不透明度的信封上的动态运动的影响。振动的本征方向（θ*）的轻微振荡，即第二斯托克斯参数（U）在这些线上的轻微振荡，被证明与cosi（其中i是恒星自转或对称轴与视线之间的角度）和其他模型参数成正比。讨论了由于模型缺乏唯一性而引起的局限性，分析了几颗最亮的早型发射星的内禀偏振观测。大多数被研究的Be星都显示出轴对称的包层（如p Car B4 Ve），但也有少数天体，如λPav（B2 II-IIIe）和μSgr（B 9 Iae）似乎有非轴对称的包层，这可能表明它们是双星。壳层星星ηCen（B1.5 V）在Hα，Hβ处显示出预测的线极化效应。
Models such as those by Capps, Coyne & Dyck explaining the continuum linear polarization in Be stars in terms of scattering and absorption in detached disk-like envelopes of ionized hydrogen are investigated in more depth. Both the time dependence and the relative wavelength dependence of the polarization may be used to differentiate between axisymmetric and non-axisymmetric envelope structures. The latter structures are particularly relevant to the case of early-type, mass-losing binary systems and suitable polarimetry can yield the orbital inclination. It is demonstrated thatallaxisymmetric, quasi-optically thin Be-star envelopes have approximately the same form of wavelength dependence of polarization in the continuum and that this dependence is controlled by the average properties of the envelope. Polarization structure across the Doppler-broadened emission lines and shell-absorption features and/or P Cygni-like profiles occurring in these circumstellar shells can be attributed to the effects of the dynamical movement of the envelope on the line opacity. A slight oscillation of the intrinsic direction of vibration (θ*), i.e. of the second Stokes parameter (U) across such lines is shown to be proportional to cosi(whereiis the angle between the stellar rotation or symmetry axis and the line of sight) and to other model parameters. Limitations due to lack of uniqueness of the models are discussed.Observations of the intrinsic polarizations of a few of the brightest earlytype emission stars are analysed. Most of the Be stars studied exhibit evidence of axially symmetric envelopes (e.g. p Car B4 Ve) but a few objects, e.g.λPav (B2II–IIIe) andμSgr (B9 Iae) appear to have non-axisymmetric envelopes which may be indicative of a binary nature. The shell starηCen (B1.5 V) displays the predicted line polarization effects at Hα, Hβ.