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Oscillations of rapidly rotating stars

快速旋转恒星的振荡

基本信息

批准号：
PP/E001815/1
负责人：
Ian Roxburgh
金额：
$ 30.9万
依托单位：
Queen Mary University of London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=PP%2FE001815%2F1
关键词：
Oscillations rapidly rotating stars

项目摘要

This research programme is to understand the oscillations of rapidly rotating stars. Gaining this understanding is crucial if we are to be able to use observational data on stellar oscillations to test and develop our understanding of the structure and evolution of stars. The frequencies of oscillation of stars are determined by their internal structure and angular velocity, so by measuring these frequencies we can in principle map, or place constraints on, their internal structure and rotation. This is stellar seismology (or asteroseismology). The frequencies of oscillations of a star can be determined from measurements of the small variations in light output, or surface velocity, over a long interval of time. For some stars this can be done from the ground, but space experiments can yield much higher precision and much longer uninterupted observations. To use this data we need to understand the oscillation properties of stars. For non-rotating, or slowly rotating stars this is relatively straight forward, each oscillation is specified by a particular surface geometrical factor (a spherical harmonic) and the number of wavelengths that fit into the star. The frequencies of models of such stars are easily calculated, and techniques have been developed for using the data to map the interiors of such stars. But for stars that are rotating the situation is much more complex; an oscillation mode is made up of several geometrical factors (surface harmonics) which makes the calculation of the oscillation frequencies much more difficult. Further rotation splits the oscillation frequencies producing a much larger frequency set. The only way to address this problem for large rotation is to make 2-dimensional computer models of rotating stars and full 2-dimensional calculations of their oscillation properties. This is the objective of the proposed research programme. This programme is now possible due to the development of techniques by Roxburgh for building realistic models of rapidly rotating stars where the rotation is not necessarily constant inside the star, and the development of techniques by LIgnieres, Rieutord and Reese to determine the oscillation of simple (polytropic) stellar models where the rotation is constant inside the star. By building on these two developments we should be able to determine the oscillation properties of realistic stellar models in non-uniform rotation. Having investigated the properties of such stellar models we will then be in a position to develop diagnostic techniques for using observationally determined frequencies to map, or place constraints on, the internal structure and rotation of rapidly rotating stars, analagous to those for non-rotaing stars. Roxburgh has considerable experience in the development of diagnostic techniques for spherical stars. It should be emphasised that rapid rotation is not that rapid. In the work of Reese on polytropic models he found that full 2-dimensional studies were needed for stars with equatorial rotation speeds greater than 50 km/s. Many, indeed most, stars of moderate and large mass have speeds greater than this. The proposal is for Reese to join Roxburgh at Queen Mary to undertake this research programme.

这项研究计划旨在了解快速旋转恒星的振荡。如果我们能够利用恒星振荡的观测数据来测试和发展我们对恒星结构和演化的理解，那么获得这种理解是至关重要的。恒星的振荡频率由其内部结构和角速度决定，因此通过测量这些频率，我们可以在原则上映射或限制其内部结构和旋转。这就是恒星地震学（或称星震学）。一颗星星的振荡频率可以通过测量长时间内光输出或表面速度的微小变化来确定。对于某些恒星，这可以从地面进行，但空间实验可以产生更高的精度和更长的不间断观测。为了使用这些数据，我们需要了解恒星的振荡特性。对于非旋转或缓慢旋转的恒星，这是相对直接的，每个振荡由特定的表面几何因子（球谐函数）和适合星星的波长数指定。这类恒星模型的频率很容易计算，并且已经开发了使用这些数据绘制这类恒星内部的技术。但是对于旋转的恒星，情况要复杂得多;振荡模式由几个几何因子（表面谐波）组成，这使得振荡频率的计算更加困难。进一步旋转分裂振荡频率，产生更大的频率集。解决大旋转问题的唯一方法是制作旋转恒星的二维计算机模型，并对其振荡特性进行全二维计算。这是拟议研究方案的目标。由于罗克斯堡开发了技术，建立了真实的快速旋转恒星模型，其中旋转不一定是恒定的星星内，以及开发了技术，由利尼耶尔，Rieutord和里斯，以确定振荡的简单（多变）恒星模型，其中旋转是恒定的星星内。通过建立在这两个发展，我们应该能够确定在非均匀旋转的现实恒星模型的振荡特性。在研究了这些恒星模型的性质之后，我们将能够开发诊断技术，利用观测确定的频率来映射或限制快速旋转恒星的内部结构和旋转，类似于非旋转恒星。罗克斯堡在球形恒星诊断技术的发展方面有相当丰富的经验。应该强调的是，快速旋转并不是那么快。在工作的里斯多方模型，他发现，充分的二维研究需要恒星的赤道旋转速度大于50公里/秒。许多，实际上是大多数中等质量和大质量的恒星的速度都大于这个速度。该提案是为里斯加入罗克斯堡在女王玛丽进行这项研究计划。