The e-MERLIN Legacy Cyg OB2 Radio Survey: Massive star feedback and evolution

出生时质量比太阳大几十倍的恒星对星系有非常重要的影响。通过这些大质量恒星的大量外流产生的能量和质量损失在天体物理学的几个基本重要领域中具有关键性的后果。与太阳等恒星不同，大质量恒星的演化是由它们一生中失去的质量所引导的。如果没有对质量损失过程的预测性理解，就完全不可能预测中子星和黑洞的相对产生率以及之前的SNe爆炸或伽马射线暴的性质和性质。考虑到第一批恒星被认为比现在的大众更加极端，这种不确定性可以追溯到早期宇宙的化学富集和演化。我们的目标是推进我们的几个（相互关联的）大质量恒星的物理过程的理解，充分利用强大的新的英国无线电设施，从2010年起由电子梅林。由于包括光纤链路和宽带在内的重大升级，e-MERLIN将成为研究大质量恒星外流及其与环境相互作用的首要国际设施。我们的研究计划建立在e-MERLIN Legacy项目（“COBRaS”; PI）的大量分配基础上，并由其分支- Prinja教授）。近300个小时的时间将用于组装一个具有真正持久价值的独特敏感数据集，这将使我们能够在三个主要的相互关联的领域提供重要的科学成果：（i）COBRaS项目将提供高度敏感的数据集，以解决目前质量损失过程中的严重不确定性，因为流出物并不平滑，但高度聚集和多孔。我们将严格测试当前关于来自热恒星的恒星风是如何驱动的理论。具体来说，利用天鹅座OB 2中独特丰富和可访问的大质量恒星群的特性，我们将能够系统地研究恒星质量损失中演化的作用。天鹅座OB 2的星族足够丰富，可以在恒星演化的每个阶段对其进行采样，从而使我们能够直接探测相应的质量损失率演化。为了理解宇宙早期的恒星演化，我们必须首先确保在外推到较低的金属性，高红移环境之前，理解当前时代的质量损失和金属性。(ii)e-MERLIN的高空间分辨率将在COBRaS项目中得到独特的利用，使用2010年至2013年期间多个时期的数据，以确定天鹅座OB 2成分的自行。将无线电数据与已经获得的光谱学相结合，将使我们能够绘制出天鹅座OB 2运动学的完整三维图像;这将是任何大质量星团的第一张这样的地图。天鹅座OB 2的基本参数和动力学将为研究星系中大质量恒星团的形成、亚结构和溶解提供新的视角。(iii)大质量恒星通常与其他大质量恒星一起出现在双星系统中，导致碰撞恒星风的现象，导致大量的X射线发射和非热无线电发射，这是一个重要的高能过程，尚未完全了解。在这个项目中，对天鹅座OB 2进行的非常丰富的射电观测将允许对大质量双星的发生率进行探测和无偏见的研究，并对碰撞风现象进行统计研究。在河外天体物理学中，了解双星频率是计算大量恒星演化的关键。双星的性质对于限制大质量星星形成的模型也是非常重要的。

Stars born with several tens times more mass than the Sun have a very significant influence in galaxies. The energetics and loss of mass through the prolific outflows of these massive stars has pivotal consequences in several fundamentally important areas of astrophysics. Unlike stars like the Sun, the evolution of massive stars is guided by how much mass they lose throughout their lives. Predictions for the relative production rates of neutron stars and black holes and the nature and properties of the preceding SNe explosion or Gamma Ray Burst are entirely impossible without a predictive understanding of the mass-loss process. And given that the first stars are thought to be even more extreme than the current populace, this uncertainty stretches back to the chemical enrichment and evolution of the Early Universe. We aim to advance our understanding of several (inter-related) processes in the physics of massive stars, by fully exploiting the powerful new UK radio facility available from 2010 onward by e-MERLIN. Due to significant upgrades that include optical fibre links and broad bandwidths, e-MERLIN is set to become the premier international facility for the study of outflows of massive stars and the interactions with their environments. Our research programme is founded on, and branches from, the substantial allocation of a e-MERLIN Legacy project ('COBRaS'; P.I. - Prof. Prinja). Almost 300 hours of already awarded time to this project will used to assemble a uniquely sensitive dataset of genuine lasting value, that will allow us to deliver important science results in three major inter-related fields: (i) The COBRaS project will deliver highly sensitive datasets to resolve serious current uncertainties of the mass-loss process due the fact that the outflows are not smooth, but highly clumped and porous. We will rigorously test the current theory of how stellar winds from hot stars are driven. Specifically, utilising the properties of the uniquely rich and accessible population of massive stars in Cyg OB2 we will be able to systematically investigate the role of evolution in stellar mass loss. The population of Cyg OB2 is rich enough that it samples stars at every stage of their evolution, thus enabling us to directly probe the corresponding evolution of mass loss rate. To understand stellar evolution at early epochs of the Universe we must first ensure that mass loss at the current epoch and metalicity is understood before extrapolating to lower metalicity, high redshift environs. (ii) The high spatial resolution of e-MERLIN will be uniquely exploited in the COBRaS project, using data over multiple epochs between 2010 and 2013, to determine the proper motions of the Cyg OB2 constituents. Combining the radio data with already secured optical spectroscopy, will permit us to map a full 3-D picture of the kinematics of Cyg OB2; this would be the first such map for any massive stellar cluster. The basic parameters and dynamics of Cyg OB2 will provide new perspectives on the formation, substructure and dissolution of massive stellar clusters in galaxies. (iii) Massive stars commonly occur in binary systems with other massive stars leading to the phenomenon of colliding stellar winds, resulting in substantial X-ray emission and also non-thermal radio emission, which is an important high energy process that is not fully understood. The very rich radio survey of Cyg OB2 assembled in this project will permit a probing and unbiased study of the incidence of massive binary stars and statistically study the colliding-wind phenomenon. Understanding the binary frequency is pivotal for computing the evolution of substantial populations of stars in extragalactic astrophysics. The binary properties are also very important to constrain models of massive star formation.