IAUS 320 – Solar and Stellar Flares and Their Effects on Planets

Recent advances in observations and modelling of solar and stellar flares have opened new perspectives for understanding of the fundamental physical mechanisms of magnetic energy storage and release, particle acceleration, and radiative and dynamical processes in solar and stellar flares. The new interest in this topic is stimulated by Kepler observations which have led to the discovery that stellar flares occur not only in M-type dwarfs (UV Ceti-type variables) but also in a wide range of A-F type stars. Previously, it was believed that the F- and A-type stars do not have flaring activity. The discovery of super-flares on solar-type stars has raised questions about the possibility of such flares on the Sun, and led to hot debates about the potential effects of such superflares on terrestrial and extra-terrestrial planets, including their impact on the origin and evolution of life. These results triggered new interest in the physical mechanism of solar and stellar flares, and their connection with the dynamo mechanism and stellar properties.

Recent observations of solar flares from the Solar Dynamics Observatory (SDO), RHESSI, STEREO, Hinode and Fermi space observatories and large ground-based telescopes have revealed details of the magnetic topology of flaring active regions, obtained important insight into the processes of magnetic reconnection and particle acceleration, and led to new understanding of the importance of local response and global-scale coupling of the flare dynamics. Among the new observations, the Fermi detection of extremely long gamma-ray emission in many solar flares is particularly surprising. These and other new results challenge the current theories of solar and stellar flares, and even cause to reconsider the whole, once well-established, paradigm about the common physical origin of the solar and stellar flares.

Previously, stellar flares associated with active M-type stars were thought to be similar to solar flares representing a sudden release of magnetic energy accumulated in the coronal part of sunspot region, in the form of high-energy particles which heat the atmosphere and corona. Stellar flares can be four orders of magnitude more powerful, which is thought be due to bigger starspot regions generated by a more efficient dynamo process, because many of the flaring stars rotate faster than the Sun. However, the new observations have raised an alternative point of view that such powerful flares may be due to the interaction with close companions - `hot Jupiters'. The discovery of flares on hot A-type stars with a very shallow outer convection zone and without strong magnetic field causes additional problems with the dynamo origin of the flare energy on these stars.

Thus, it is very timely and important to hold broad interdisciplinary discussions focused on the origin of solar and stellar flares, and their effects on planets. This topic is of great interest to members of four IAU Divisions:
Division D High Energy Phenomena and Fundamental Physics,
Division E Sun and Heliosphere,
Division F Planetary Systems and Bioastronomy,
Division G Stars and Stellar Physics.
The IAU General Assembly provides a unique opportunity for this symposium, which is likely to attract more than 300 participants. The previous IAU meeting on the topic of solar and stellar flares was IAU Colloquium 104 in 1988. Typically, solar and stellar flares are discussed separately: solar flares at the annual RHESSI workshops, and stellar flares at the Cambridge Workshops on Cool Stars. In June 2014, there will be a conference on solar and stellar flares in Prague, which will have five sessions: 1) Flare processes in the corona, 2) Response of the lower atmosphere to flare processes, 3) Flare-related CMEs, 4) Stellar flares, 5) New instrumentation for flare research. This conference, which will discuss details of some of the key elements of the flare process, will provide an excellent opportunity to prepare for a broader IAU Symposium in 2015, focused on interdisciplinary connections among the flare phenomena across the HR diagram and their effects on planets. Profs Heinzel and Shibata are SOC members of the Prague conference and also Co-Chairs of the IAU Symposium. This will allow us to select the most interesting new advances presented in Prague for invited presentations to the broader audience at the IAU Symposium, and also avoid duplicated talks.

This Symposium will be a forum for discussing the recent advances in observations and theories of solar and stellar flares, focused on the understanding of their phenomenological and physical aspects, as well as consequences for terrestrial planets and exoplanets. It will cover a broad range of phenomena, from the magnetic topology of flares and mechanisms of impulsive energy release to high-energy flare emission and potential impacts on planets.