Jørgen Christensen-Dalsgaard – författare

The existence of strongly convecting layers in the Sun and stars provides us with a natural laboratory for the study of dynamical processes in intensely turbulent, magnetized, rotating, radiating fluids. Helioseismology h as now given us a tool to measure the detailed properties of solar convection beneath the visible Sun, and thus to test our understanding of the nature of convection and of its influence on stellar structure and the radiative magnetohydrodynamics of solar convection. Presenting and incorporating the newest results from numerical hydrodynamic simulations and helioseismic observations, these contributed papers present the very latest developments in each of these fields.

The continuing success of helio and asteroseismology in studying the internal structure and dynamics of the Sun, and of other single stars, has been highlighted in recent years by many topical meetings. The present Proceedings document the first seismology symposium ever held in conjunction with an IAU General Assembly. This substantially influenced the layout of the scientific programme and demonstrates the vitality of this field of astronomy. The invited reviews are intended to address an audience that includes many non-specialists. Therefore, this volume is an introduction to the general concepts of the field. There are two chapters on the many facets of asteroseismology, which also compare solar and stellar achievements. A major focus of the symposium was the new developments resulting from the observations of unprecedented quality obtained from global multi-site networks, and especially from the solar and heliospheric observatory SOHO, currently continuing its observations from the Lagrangian point L1.From the centre of the Sun to its outer layers, the reader will learn how modern diagnostic techniques reveal the inextricable links between the complex structure of the interior and atmosphere of our nearest star. The book is recommended for undergraduates, postgraduates, and professionals with an interest in modern developments in astrophysics.

The cover picture of this volume displays one of the most advanced products of he­ lioseismic research: a view into the deep interior of the sun, revealing its distinctly non-uniform rotation throughout the entire depth of the convection zone. Just over 20 years ago, the first successful helioseismic experiment disclosed an increase of ro­ tation velocity in the uppermost one dozen megameters below the photosphere. The stunning progress in depth and detail highlighted by the cover diagram (and by others shown in this volume as well) was made possible by considerable advances in instru­ mentation, by the development of powerful analytical tools and, foremost, by the involvement of new brains of enthusiastic proselytes and newcomers to the field, in­ creasing nearly exponentially in number every year. New branches of research widened the scope of "uranoseismology", as e. g. time-distance seismology (the promising av­ enue towards small-scale and short-time variability), atmospheric seismology (a new look at strange phenomena we have all ways seen, but hardly understood), and finally the growing observational assault on hundreds of individual stars which are either manifestly or supposedly oscillating -i. e. asteroseismology. The formation of numer­ ous solar and stellar observing networks and, ultimately, space missions like SOHO have greatly promoted the potential of this science. This steady progress was accompanied by workshops, colloquia, and symposia in quick succession.

These are the proceedings of a meeting celebrating Michael Thompson's seminal work on solar and stellar physics, as well as his major contributions to the development of the National Center for Atmospheric Research. The meeting also marked Michael J. Thompson’s untimely death in October 2018. Michael played a key role in the development of helioseismology and its application to the study of the structure and dynamics of the solar interior, and he provided a strong foundation for the extension of seismic studies for other stars. After focusing for several years on more administrative activities, he was returning to leading the seismic studies of solar interior rotation and he was deeply involved in the understanding of the dynamics of the core of stars, when his life was tragically lost.The conference focused on dynamical aspects of the sun and stars, based on the large amount of data available on solar and stellar oscillations, and the extensive and detailed modelling now becoming feasible. Combining observations, seismic analysis, and modelling the meeting and this book serve as a fitting memorial to a close colleague and friend, much missed.

Helio- and asteroseismology study the interior of the Sun and other stars, by means of observations of oscillations on their surfaces. The last 10 years in the study of the solar interior, to a has witnessed a very rapid evolution point where we can now contemplate investigating the physical state of matter, or the details of rotation and other large-scale motion, in the Sun. The stellar studies are in some respects at the point of the solar studies 10 years ago, but appear poised to take off. Thus the time was deemed ripe for lAO Symposium No 123, to assess the present status of this work, and plan for its future development. Apart from the seismic data, few observations are available to provide information about stellar interiors. Detailed studies, by spectral analysis, can be made of stellar surface properties, including atmospheric temperature and chemical composition. However, the stellar radiative spectrum is almost entirely fixed by the mass, luminosity, radius and surface rotation of the star, and contains essentially no other information about the interior. An important test of stellar evolution theory is provided by observations of stel­ lar clusters, whose members can reasonably be assumed to have the same age and chemical composition. The location of such stars in a HR diagram, where luminosity is plotted against the effective temperature, can roughly be understood in terms of stellar evolution calculations.