Classical Be Stars
Classical Be Stars
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DOI：
10.1007/s00159-013-0069-0
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发表时间：
2003-10
影响因子：
3.5
通讯作者：
J. Porter;T. Rivinius
中科院分区：
文献类型：
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作者：
J. Porter;T. Rivinius
在过去的十年里，关于经典Be星的性质已经达成了共识：它们是非常快速旋转的主序星B，通过一个仍然未知但越来越受限制的过程，形成了一个向外扩散的气体，无尘的开普勒盘。在这项工作中，首先Be星的定义进行了对比，类似的类，和常见的观测得到的Be星和解释各自的形成机制。然后，我们回顾了目前关于中心恒星作为非径向脉动天体和非磁性恒星的知识状况，只要它涉及大尺度，即，大部分是偶极的全局场局部的弱磁场仍然是可能的，但尚未得到证实。Be现象，与一个或多个质量喷射过程相关联，作用于约75%临界或以上的旋转速率之上。该过程的性质可以很好地受到约束，只留下很少的选择，最重要的是，但不排他的，非径向脉动和小规模磁场。其中，很有可能所有这些都实现了：在不同的恒星中，不同的过程可能正在起作用。一旦物质被提升到开普勒轨道，对喷射过程细节的记忆就消失了，物质的粘度就决定了。在粘滞衰减圆盘模型的理论框架中，对圆盘有相当好的理解。这不仅适用于盘的结构，而且也适用于它的周期性和长期性的变化。Be双星的审查方面的各种类型的相互作用的一个同伴可以与拱盘。最后，河外Be星，在较低的金属丰度，似乎更常见，更迅速地旋转。
In the past decade, a consensus has emerged regarding the nature of classical Be stars: They are very rapidly rotating main sequence B stars, which, through a still unknown, but increasingly constrained process, form an outwardly diffusing gaseous, dust-free Keplerian disk. In this work, first the definition of Be stars is contrasted to similar classes, and common observables obtained for Be stars are introduced and the respective formation mechanisms explained. We then review the current state of knowledge concerning the central stars as non-radially pulsating objects and non-magnetic stars, as far as it concerns large-scale, i.e., mostly dipolar, global fields. Localized, weak magnetic fields remain possible, but are as of yet unproven. TheBe-phenomenon, linked with one or more mass-ejection processes, acts on top of a rotation rate of about 75 % of critical or above. The properties of the process can be well constrained, leaving only few options, most importantly, but not exclusively, non-radial pulsation and small-scale magnetic fields. Of these, it is well possible thatallare realized: In different stars, different processes may be acting. Once the material has been lifted into Keplerian orbit, memory of the details of the ejection process is lost, and the material is governed by viscosity. The disks are fairly well understood in the theoretical framework of the viscous decretion disk model. This is not only true for the disk structure, but as well for its variability, both cyclic and secular. Be binaries are reviewed under the aspect of the various types of interactions a companion can have with the circumstellar disk. Finally, extragalactic Be stars, at lower metallicities, seem more common and more rapidly rotating.