Magnetic fields: the key to understanding the physics of stellar evolution and exoplanetary systems

磁场：理解恒星演化和系外行星系统物理学的关键

• 批准号: ST/J003255/1
• 负责人: Scott Gregory
• 金额: $ 54.47万
• 依托单位: University of St Andrews
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FJ003255%2F1
• 关键词: Magnetic; fields; key; understanding; physics

Some of the most intense solar fireworks have directly affected modern life on Earth. Rapid increases in solar activity send fluxes of charged particles towards our planet, disrupting satellite communications and generating spectacular aurorae. The sublime coloured lights flickering across the night sky arise from solar wind particles trapped in the large-scale magnetic field of the Earth. We are fortunate that this magnetic field protects our atmosphere, and us, from the harmful effects of the highest energy solar radiation. Yet however spectacular the events on our Sun may seem today, our middle-aged star is comparatively quiet and hides a much more violent past. A few billion years ago the Sun was a contracting ball of hot gas, although it was still too cool within its core to fuse hydrogen into helium and shine as it does today. Young solar analogues, called T Tauri stars, are about a million times too faint to be seen with the naked eye. Space satellite observations, however, have shown that they are typically 1000 times more active in X-rays than the Sun is presently. They are surrounded by large dusty planet-forming discs, which are bombarded by X-rays arising from violent stellar magnetic events. T Tauri stars are new-born stars which are still shrinking down under gravity to their adult proportions. As such stars collapse they should start to spin faster and faster, just like an ice-skater who pulls in their arms closer to their body. However, such stars are observed to be spinning slowly, an effect that has been attributed to how their strong magnetic fields interact with the gas and dust within the surrounding discs. T Tauri stars are embedded in a web of magnetic field which binds them to their discs, the eventual birthplace of planetary systems. It is expected that this magnetic web acts as a brake, allowing the star to remain spinning slowly. This process, however, is poorly understood.Using a technique called Zeeman-Doppler imaging, which is analogous to methods used in medicine to produce 3D images of the internal organs of the body, I have been able to determine the structure of their magnetic webs. This newly available data signals the beginning of a fresh era of research into the formation of solar-like stars. My research will exploit information gained from the largest telescopes on Earth and from space satellites in order to investigate how forming stars interact with, and disrupt, their environments. The significant gains in observational results require corresponding development of state-of-the-art numerical models. Ultimately my research will provide insight into the formation of our own Sun, and Solar System, at a time when the planets were just beginning to form.Roughly 500 planets, exoplanets, have now been found orbiting other stars with potentially thousands more awaiting discovery by the currently operating Kepler satellite. Some of the exoplanet host stars twinkle on the same timescale as it takes their planets to complete an orbit. This effect may be caused by the planets twisting the strands of the star's magnetic web; this process, if it can be understood, may provide a method of determining the magnetic properties of the exoplanets themselves. I will investigate star-planet interaction in detail during the STFC Ernest Rutherford Fellowship.

一些最强烈的太阳焰火直接影响了地球上的现代生命。太阳活动的迅速增加将带电粒子流射向我们的星球，扰乱了卫星通信并产生了壮观的极光。在夜空中闪烁的彩色光芒是由被地球大磁场捕获的太阳风粒子产生的。我们很幸运，这个磁场保护我们的大气层和我们免受最高能量太阳辐射的有害影响。然而，无论太阳上发生的事件在今天看起来多么壮观，我们的中年恒星相对来说是安静的，它隐藏着一个更加狂暴的过去。几十亿年前，太阳是一个由热气体组成的收缩球，尽管它的核心仍然太冷，无法像今天这样将氢聚变成氦并发光。年轻的类似太阳的恒星，被称为金牛座T星，亮度大约是肉眼的一百万倍。然而，太空卫星观测表明，它们在x射线上的活跃程度通常是目前太阳的1000倍。它们被巨大的行星形成盘所包围，这些盘被剧烈的恒星磁事件产生的x射线轰击。金牛座T星是新生的恒星，在重力作用下仍在缩小到成年的比例。当这样的恒星坍缩时，它们应该开始旋转得越来越快，就像滑冰运动员把手臂拉向身体一样。然而，观察到这样的恒星旋转缓慢，这种效应归因于它们的强磁场如何与周围圆盘内的气体和尘埃相互作用。金牛座T型恒星嵌在磁场网中，磁场网将它们与它们的行星盘捆绑在一起，行星盘是行星系统的最终诞生地。预计这个磁网起到了刹车的作用，使恒星保持缓慢旋转。然而，人们对这一过程知之甚少。使用一种叫做塞曼-多普勒成像的技术，这种技术类似于医学上用来产生人体内部器官3D图像的方法，我已经能够确定它们磁网的结构。这些新获得的数据标志着研究类太阳恒星形成的新时代的开始。我的研究将利用从地球上最大的望远镜和太空卫星获得的信息，以调查形成的恒星如何与它们的环境相互作用，并破坏它们的环境。观测结果的显著进步要求相应发展最先进的数值模式。最终，我的研究将为我们的太阳和太阳系的形成提供见解，当时行星刚刚开始形成。目前已经发现了大约500颗行星，系外行星，围绕其他恒星运行，可能还有数千颗等待开普勒卫星的发现。一些系外行星的宿主恒星在相同的时间尺度上闪烁，因为它们的行星需要完成一个轨道。这种效应可能是由于行星扭曲了恒星的磁网；如果这个过程能够被理解，可能会提供一种确定系外行星本身磁性的方法。我将在STFC欧内斯特·卢瑟福奖学金期间详细研究恒星-行星相互作用。

项目成果

Magnetospheric accretion on the fully convective classical T Tauri star DN Tau

• DOI: 10.1093/mnras/stt1622
• 发表时间: 2013-08
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: J. Donati;S. Gregory;S. Alencar;G. Hussain;J. Bouvier;M. Jardine;F. Ménard;C. Dougados

Magnetic activity and hot Jupiters of young Suns: The weak-line T Tauri stars V819 Tau and V830 Tau

• DOI: 10.1093/mnras/stv1837
• 发表时间: 2015-09
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: J. Donati;E. H'ebrard;G. Hussain;C. Moutou;L. Malo;K. Grankin;A. Vidotto;S. Alencar;S. Gregory;M. Jardine;G. Herczeg;J. Morin;R. Fares;F. M'enard;J. Bouvier;X. Delfosse;R. Doyon;M. Takami;P. Figueira;P. Petit;I. Boisse;the MaTYSSE collaboration

Hot Gas Lines in T Tauri Stars

T Tauri Stars 中的热气管线

• DOI: 10.48550/arxiv.1304.3746
• 发表时间: 2013
• 作者: Ardila D

The hot Jupiter of the magnetically active weak-line T Tauri star V830 Tau

• DOI: 10.1093/mnras/stw2904
• 发表时间: 2016-11
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: J. Donati;J. Donati;Louise Yu;Louise Yu;C. Moutou;A. C. Cameron;L. Malo;K. Grankin;E. H'ebrard;G. Hussain;A. Vidotto;S. Alencar;R. Haywood;J. Bouvier;Pascal Petit;Pascal Petit;M. Takami;G. Herczeg;S. G. Gregory;M. Jardine;J. Morin

Inner disk structure of the classical T Tauri star LkCa 15

• DOI: 10.1051/0004-6361/201834263
• 发表时间: 2018-11
• 期刊: Astronomy & Astrophysics
• 影响因子: 6.5
• 作者: S. Alencar;J. Bouvier;J. Donati;E. Alecian;C. Folsom;K. Grankin;G. Hussain;C. Hill;A. Cody;A. Carmona;C. Dougados;S. Gregory;G. Herczeg;F. M'enard;C. Moutou;L. Malo;M. Takami;the MaTYSSE collaboration