Magnetic fields and stellar evolution

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All stars are natural magnets, thanks to the dynamic, electrically conductive gases that compose them. And because the magnetic fields of stars can be very strong, they represent a basic element in astrophysicists' theory of stellar structure and evolution. In recently years it has been clearly demonstrated that magnetic fields have essential impacts on stellar lives, modifying their interior flows of gas, changing their internal rotational profiles and distributions of nucleosynthetic chemicals, channeling and modifying their outflowing winds, and slowing their surface rotation through so-called "magnetic braking". Ultimately, these effects result in important changes in the evolution of stars, leading in particular to modifications of the relationships between stellar temperatures, luminosities, sizes and ages. They also influence the important outputs of stars in terms of the mass and luminous energy injected into the surrounding interstellar medium during their lives. More remarkably, they can also influence the dramatic supernova explosions that mark the deaths of the most massive stars. These effects directly impact the properties of exotic remnant white dwarf and neutron stars, and change how populations of stars contribute to the structure and chemistry of their local Galactic environments. *** As stars age and evolve, so too do their magnetic fields. Hence we expect to observe important transformations of stellar magnetic fields as stars pass through various stages of nuclear burning and undergo large changes to their temperatures, luminosities and sizes. As a consequence, the magnetic field of a star at one stage of its life may appear very different from that at a later stage. It is therefore of great interest to understand the relationships between magnetic fields observed in stars at very different evolutionary stages. For example, can the magnetic fields from an earlier evolutionary stage "seed" the production of a very different magnetic field at a later stage? Do magnetic fields with similar characteristics in stars at very different evolutionary stages have any direct relationship? ***With my research team of Canadian and international students and scientists, I am working to answer many of the questions prompted by the issues described above. The principal aim of the research described in this proposal is to continue my group's systematic exploration of the characteristics of magnetic fields of stars of all types, using telescopes around the globe and in space. My proposal has two main goals: to quantitatively understand how magnetic fields influence stellar structure and evolution, and to understand how the observable magnetic fields of stars transform over stellar evolutionary timescales. *** **