Principal topics:

The most critical aspects of the solar and stellar variability and its impact on the Earth and planets, including:

  • physical mechanisms of solar and stellar variability
  • solar diameter and irradiance measurements
  • helio- and asteroseismic inferences
  • variability of spectral irradiance and energetic particles
  • solar cycles and variability on century timescale
  • effects on space weather and solar system planets
  • implications for Earths climate
  • stellar magnetic activity and cycles
  • brightness changes in solar-type stars and stellar surface structures
  • effects of magnetic activity on planet formation and evolution
  • space and ground-based observational projects.


    Scientific Rationale

    The Sun is a variable star. Understanding the physical mechanisms of the variability and its effect on the Earth and planets is one of the central and long-standing problems of astronomy and astrophysics. Variability of the similar type has been observed in other stars. It has been realized that it is essential to investigate the similarities and differences between solar and stellar variabilities in order to understand the physical mechanisms and impacts on planets.

    During the past decade multi-wavelength observations from several solar and stellar space missions (including Ulysses, SOHO, Hinode, TRACE, RHESSI, XMM Newton, Chandra, Hubble Space Telescope) and ground-based observatories have provided tremendous amount of new information about the physical processes on the Sun and solar-type stars associated with their magnetic activity and variability.

    The recent solar observations have provided new data about the solar-cycle variations of the structure and dynamics from the interior to the corona and heliosphere. They showed interesting connections between the interior dynamics, surface magnetism and coronal phenomena. However, despite the great amount of new data it is still unclear where and how magnetic fields are generated in the Sun, and why it has a regular 22-year magnetic cycle. Can observations of other stars help us to understand the solar magnetic cycle, which is so important not only for astrophysics but also for our life and society? What are the essential components of the solar variability?

    Recent optical, UV and X-ray observations of other stars with significant subsurface convection zones (lower main sequence stars with masses smaller than 1.5 solar masses and cool post-main-sequence stars) reveal starspots and other surface and atmospheric structures that are similar to solar magnetic features. In many cases, the long-term evolution of these features is similar to the solar cycle. Advances in the Doppler imaging technique has allowed obtaining maps of starspot distribution and tracking their evolution. This led to first accurate measurements of the stellar differential rotation, a key property of dynamo mechanisms. In addition, UV and X-ray observations detected stellar coronas similar to the solar corona. Thus, it is very important and timely to discuss the whole complex of the interlinked active phenomena on the Sun and other stars.

    Observations also show significant differences between solar and stellar activities, which make impossible a direct extrapolation from the complexity of the atmospheric and interior structure observed on the Sun to solar-type stars. However, there is a single main ingredient that acts as the driving mechanism for activity in all atmospheric layers and the convective envelope: the dynamo-driven magnetic field. Thus, the new observations of the cycles of activity on the Sun and other stars provide important constraints for theoretical models of solar dynamo and stimulate development of new ideas.

    The impact of the solar variability on the Earth, particularly on the Earth atmosphere and climate, has been a subject of significant debates in recent years. There is no doubt that solar radiation is the major source of terrestrial energy. The solar activity cycle causes changes in the Earth's temperature and density, especially in the thermosphere. Energetic particles cause geomagnetic storms and energy input into the magnetosphere and the polar regions of the atmosphere, which also varies with the solar cycle. The variations of the energy input may potentially cause changes in the climate. However, the full chain of the impact of the solar variability is not understood. This problem is not only of the great practical importance, but also directly related to one of the most important astronomical problem: how the stellar variability and activity affects exoplanetary systems and their habitability.

    The detection of planet systems around other stars have yielded a tremendous boom to studies linked to understanding of mechanisms of planets formation, a new major astrophysical task, which, in turn, leads to the comprehension of our own origins. In the last decade, more than 160 planetary systems have been detected providing grounds for testing models of planet formation and evolution. Apart the possibility of determining the mass, radius and orbital parameters of the planets, it is now increasingly possible to determine their composition, temperature, the presence of clouds, their magnetic fields and even their space environment (moons or rings). The new era of dedicated space telescopes or ground-based very large telescopes will provide spectroscopic studies aiming to detect biomarkers for understanding how life in the Universe was born.

    The scientific aims of the 3 ½ -day Symposium are to discuss the most important results of the recent observations of solar and stellar activity, similarities and differences between characteristics of the solar and stellar cycles, variability on the century timescale, relationships between the cyclic behaviour and stellar properties, the progress in theories and numerical simulations of the dynamo mechanism, variation of the solar diameter and irradiance, effects on the climate and space weather on Earth and other Solar System planets, potential impact of stellar magnetic activity on formation and evolution of exoplanets, and other hot topics of solar-stellar and related planetary physics. The Symposium will stimulate discussions and cooperation among solar and stellar astronomers, and develop new ideas about variability and activity of our Sun and other stars and impacts on the Earth and planets.

    Editors: Alexandre H. Andrei, Alexander Kosovichev & Jean-Pierre Rozelot