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Two Dimensional Stellar Evolution

二维恒星演化

基本信息

批准号：
ST/M003892/1
负责人：
Christopher Tout
金额：
$ 33.57万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=ST%2FM003892%2F1
关键词：
Two Dimensional Stellar Evolution

项目摘要

* ContextStars are, for the most part, spherical objects. For this reason, theoretical and computational models of stars are usually assumed to be just that: they are spheres. Such models work amazingly well and the those working in the field of stellar evolution have, for a century or so, exploited them very successfully. We now understand how stars burn hydrogen to helium to make them shine for billions of years, for example.However, in the last decade, it has become increasingly clear that many of the most exciting stars are not the simple, spherical objects we are used to. Rotation is key. Stars that rotate expand around their equator with important consequences for their internal structure. Some stars, known as the Be stars, rotate is so fast that they are nearly flying apart. These stars are more egg-shaped than spherical!Existing models of these rotating stars make some assumptions about their internal structure to construct distorted sphere models which are based on spherical models with small, non-spherical perturbations. These assume, for example, that stars rotate as nearly-spherical shells internally. Compare this to the internal structure of our Sun. At first glance it is spherical but we know from observing sunspots that it rotates once every 24 days at the equator. This is slow rotation because the distortion at the solar surface is very small. Even so the internal rotation is not on shells - latitudinal differential rotation is visible at the surface and helioseismolgy confirms that this differential rotation extends through the convective zone. In the interior it appears to rotate more solidly.Many stars rotate much faster than the Sun and show far more severe physical symptoms. For example, rotation causes mixing of material from the centre of the star to its surface, leading to chemical pollution which can be observed with our telescopes. If, as in the Sun, the rotation rate changes with depth, we expect a dynamo to generate magnetic fields in the star. In binary-star systems material can move from one star to the other. This can spin up a star to its maximum, break up, rotation rate and induce significant chemical mixing and magnetic field formation. In turn magnetic fields transport angular momentum.* Aims, objectives and applicationsThese processes can be modelled with simple spheres. A multi-dimensional model of a star is much more apt and that is the ultimate aim of this project. While three-dimensional stellar evolution is not currently possible because computers are simply not fast or powerful enough, two-dimensional stellar evolution is within our grasp. In two dimensions the fundamental processes of rotation and magnetic fields can be modelled properly without the many, often poorly justified, assumptions currently employed in stellar evolution models. The leap from one to two dimensions is a big. It needs to be made carefully. The first achievable goal is to model two-dimensional stellar evolution by writing a new code to self-consistently solve for the structure of stars in two dimensions. This will include, as standard features, stellar rotation, magnetic field generation by dynamos, nuclear burning in the core of the star, mixing throughout the star and basic binary star interactions. The models will cover evolutionary phases from hydrogen burning, like our Sun, through red giants and supergiants, the biggest and brightest stars known, to stellar death.The models constructed in this project will be made available to collaborators. This include the BRIDGCE project in the UK, to study the impact of rotation in stars on the chemical evolution of galaxies. Internationally the VLT-FLAMES collaboration needs stellar evolutionary models to interpret and understand the rapidly rotating stars they observe. The results of this project will be ideal for this task and for comparison with other surveys such as that made by NASA's Kepler satellite.

* ContextStars在大多数情况下是球形对象。由于这个原因，恒星的理论和计算模型通常被假设为：它们是球体。这种模型的工作效果令人惊讶地好，那些在恒星演化领域工作的人，在大约世纪的时间里，非常成功地利用了它们。例如，我们现在知道恒星是如何将氢燃烧成氦，使它们发光数十亿年的。然而，在过去的十年里，越来越清楚的是，许多最令人兴奋的恒星并不是我们所习惯的简单的球形物体。旋转是关键。旋转的恒星围绕赤道膨胀，对它们的内部结构产生重要影响。有些恒星，被称为Be星，旋转得如此之快，以至于它们几乎飞离。这些星星更像是蛋形的而不是球形的！这些旋转恒星的现有模型对它们的内部结构做出了一些假设，以构建基于具有小的非球形扰动的球形模型的扭曲球模型。这些假设，例如，恒星旋转作为近球形壳内部。将其与我们太阳的内部结构进行比较。乍一看，它是球形的，但我们通过观察太阳黑子知道，它在赤道每24天旋转一次。这是缓慢的旋转，因为太阳表面的扭曲非常小。即便如此，壳层上也没有内部旋转--表面可以看到纬向差异旋转，日震学证实这种差异旋转延伸到对流区。在其内部，它的旋转似乎更加稳固，许多恒星的旋转速度比太阳快得多，并且表现出严重得多的物理症状。例如，旋转导致从星星中心到表面的物质混合，导致化学污染，这可以用我们的望远镜观察到。如果像太阳一样，自转速率随深度而变化，我们就可以预期星星中会有发电机产生磁场。在双星星星系统中，物质可以从一颗星星移动到另一颗。这可以使一颗星星旋转到最大，分裂，旋转速度和诱导显着的化学混合和磁场形成。反过来，磁场传递角动量。目的、目标和应用这些过程可以用简单的球体来模拟。星星的多维模型更合适，这是这个项目的最终目标。虽然三维恒星演化目前还不可能，因为计算机根本不够快或足够强大，但二维恒星演化已经在我们的掌握之中。在二维空间中，旋转和磁场的基本过程可以被恰当地模拟，而不需要目前恒星演化模型中所采用的许多通常不合理的假设。从一维到二维的飞跃是巨大的。它需要仔细制作。第一个可实现的目标是通过编写一个新的代码来自洽地解决二维恒星结构的二维恒星演化模型。这将包括，作为标准特征，恒星旋转，发电机产生的磁场，星星核心的核燃烧，整个星星的混合和基本的双星星星相互作用。这些模型将涵盖从氢燃烧（如太阳）到红巨星和超巨星（已知最大和最亮的恒星）再到恒星死亡的演化阶段。这包括英国的BRIDGCE项目，研究恒星旋转对星系化学演化的影响。在国际上，VLT-FLAMES合作需要恒星演化模型来解释和理解他们观察到的快速旋转的恒星。该项目的结果将是这项任务的理想选择，并可与美国宇航局开普勒卫星等其他调查进行比较。