The Winds of Wolf-Rayet Stars: Their strength and Structure

如果没有大质量恒星，宇宙将会大不相同。事实上，它们构成了恒星和星系中的星际介质之间交换物质的主要手段，尤其是化学丰富的物质。大多数比碳更重的元素都是在其核心内制造的，它们通过超新星爆炸以一种壮观的方式注入到周围的介质中。但在它们短暂的生命过程中，大质量恒星也会以强烈的恒星风的形式，不断地向星际介质注入物质、能量和动量。我的研究不仅是确定大质量恒星损失了多少质量，而且还确定了它是如何损失的；风的结构是什么。我研究的最多的恒星被命名为Wolf-Rayet(WR)恒星，以纪念19世纪末发现它们的两位科学家。这些恒星一般都是大质量恒星，已经达到了在其核心燃烧氦的阶段。 近年来，我开始对一种特殊的结构感兴趣，这种结构存在于大约20%的WR恒星的风中，它打破了风的球面对称性。这些结构被称为共转相互作用区(CIR)。关于CIR的有趣之处在于，它们被认为是由磁场或恒星脉动产生的，非常接近恒星表面，而这一区域被稠密的风很好地隐藏起来，因此很难研究。由于风中有CIR，WR恒星在其光线和光谱中显示出大范围的周期性变化。由于CIR被认为固定在恒星表面附近的区域，所以这一周期与恒星的自转速度有关。WR恒星的自转速度没有其他测量方法，因为传统的方法由于浓密的风而失效。 通过研究WR风中的CIR，我希望测量WR恒星样本的自转速度，并了解我们目前几乎一无所知的物理机制，即磁场和脉动。

The Universe would be very different without massive stars. Indeed, they constitute the principal means by which material, and more particularly chemically enriched material, is exchanged between stars and the interstellar medium in galaxies. Most elements heavier than Carbon are fabricated within their core and they are injected into their surrounding medium in a spectacular way via supernova explosions. But throughout their short lives, massive stars also steadily inject matter, energy and momentum into the interstellar medium of galaxies in the form of a strong stellar wind. My research is about determining not only how much mass is lost by massive stars but also how it is lost; what is the structure of the wind. The stars I work on the most are named Wolf-Rayet (WR) stars in honor of the two scientists that discovered them at the end of the 19th century. These are generally massive stars that have reached the stage of burning Helium in their core. In recent years, I have become interested in a particular form of structure that are present in the winds of approximately 20% of WR stars and that break the spherical symmetry of the winds. These structures are called Corotating Interaction Regions (CIRs). What is interesting about CIRs is that they are thought to be generated by either a magnetic field or stellar pulsations very close to the surface of the star, a region which is well hidden by the dense wind and therefore very difficult to study. As a consequence of having CIRs in their winds, WR stars show large-scale periodic variability in their light and spectrum. As CIRs are thought to be pinned to a region close to the stellar surface, this period is related to the rotation rate of the star. Rotation rates of WR stars have no other way of being measured, as traditional methods fail because of the dense winds. By studying CIRs in WR winds, I hope to measure the rotation rate of a sample of WR stars and to learn about physical mechanisms, i.e. magnetic fields and pulsations, about which we presently know almost nothing.