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===== Seismology of the Sun, Stars, and Giant Planets =====

{{ :wiki:science:bounces.gif?direct|250|}}

The Sun and many stars ring like a bell, as they are filled with acoustic waves excited by turbulent convection (see animation on right). These waves can be used to "see" into the solar interior using a technique called helioseismology. A useful analogy is Earth seismology. When an earthquake occurs, acoustic "sound" waves generated at the source travel deep into the Earth's interior and refract back towards the surface, where they are subsequently measured by seismographs. Comparisons of the observed travel times and amplitudes of the waves with theoretical models of the expected values allow geophysicists to infer sub-surface properties.



The situation is very similar in the case of the Sun and stars. Waves are continuously excited and travel throughout the stellar interior, some even all the way to the core. They then are refracted back to the surface where they can be measured using ground- and space-based telescopes. For the Sun, the information in the waves tells us about flows, rotation, sound speed, chemical abundances, asphericity, and magnetic fields along the areas where the waves traveled. Helioseismology has given us fascinating insights about the structure of the Sun. For stars, rotation and structure can be inferred from the frequencies of the waves.



[{{:wiki:science:sun-meridional-zhao.jpg?nolink&200 |The possible structure of the meridional flows in the Sun's convection zone. Such a configuration is a puzzle for those who try to determine how the Sun generates its magnetic fields. Adapted from Zhao et al. (2013).}}]

The most important unsolved problems in solar physics concern the generation and evolution of magnetic fields. The Sun has a dynamo, not well understood, that creates its magnetism. The research objective of this project is to provide tight constraints on interior dynamo models so that a better understanding of the Sun and solar-cycle dynamics becomes possible. 

This can be achieved by measuring the large-scale plasma flows throughout the entire solar convection zone with unprecedented accuracy using local helioseismology. The role of rotation and interior flows such as the meridional circulation in driving the solar cycle is unquestioned. Key characteristics of the flows are still largely uncertain, such as their depth dependence, strength, and time variation. Yet, as ingredients to dynamo models of solar magnetic fields, such quantities are critically needed. On the left is a recently obtained insight into what the meridional flows structure may look like. Our research attempts to determine this information.