Living Reviews in Solar Physics: "Magnetism, dynamo action and the solar-stellar connection"
Brun, A.S. & Browning, M.K., Magnetism, dynamo action and the solar-stellar connection, Living Rev Sol Phys (2017) 14: 4. https://doi.org/10.1007/s41116-017-0007-8
Open Access | Review Article
First Online: 26 September 2017
"The manuscript is a very welcome overview about dynamos in stars. It presents a very broad and well written overview about the research fields related to stellar dynamos connecting observational results with simulations. A lot of useful information is collected. The authors cover all relevant stellar environments from high-mass stars, low-mass stars, stars with different convective properties, the Sun, Brown Dwarfs, and planets. Both observational and modeling results are presented with an emphasis on the presentation of recent modeling results. This kind of a review, in particular the simulations and their connection to empirical results, is clearly missing in the literature."
The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star’s life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism—e.g., its dependence on stellar age, mass, or rotation rate—that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the “Solar-stellar connection”: i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred) in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases) on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief summary of what we have learned, and a sampling of issues that remain uncertain or unsolved.
Dr. Allan Sacha Brun is Head of the Laboratory 'Dynamics of Stars, (Exo-)Planets, and their Environment' (LDE3), Service d'Astrophysique, SEA-Saclay, France.
Dr. Matthew K. Browning is an Associate Professor at the Department of Physics and Astronomy, University of Exeter, UK.