Diagnosis and heating the outer layers
- Heating of the solar corona
The high solar atmosphere (the corona) has the amazing feature of maintainig temperatures of about a million degrees, with episodes in which the temperature may be even higher, while the surface of the Sun does not reach 6000 degrees. These temperatures can only be explained if the thermal energy losses (conduction, convection and radiation) are offset by a significant dissipation of energy, probably of magnetic origin.
The physical processes leading to dissipation are complex and involve very large (100000 km) and very small (100 m) scales. The existence of small scale probably created by turbulence is essential for mechanism dissipation to be effective. Yet, beyond the issue of explaining the observations of hot plasma in the corona, it is important to understand these processes both because they could explain the formation of the corona of stars other than the Sun, and also because they are involved in the relationship between the Sun and Earth, sometimes tumultuous during solar storms.
The activities of the team on this subject are mainly the statistical study of heating events, simulation of their observable effects, observation of wave dissipation and heating of polar plumes in coronal holes.
- Solar prominences and eruptive phenomena
Solar prominences are large-scale magnetic structures where a cold and dense plasma (less than 104K) is confined within the vast, hot (106 K) and diluted corona. In itself, the very existence of these structures is a challenge for physicists, both in terms of balance of forces and energy. As a prominence (commonly called filament when seen on the disk as an extended dark region) is always at the top of a polarity inversion of the magnetic field, one can easily imagine the role of the Lorentz force to prevent matter from falling. Actually, the situation is obviously more complex, not least because of the presence of a filamentation of matter, variable in both time and space, by the nature of plasma hesitating between fully ionized and completely neutral, and the propagation of various wave dissipation, etc ...
The very existence and evolution of these structures provide a natural laboratory for astrophysical plasmas, but another reason for studying them is the important role they play in association with eruptions and CMEs in Space Weather.
- Magnetic activity of stars
Magnetism plays a major role in the physics of stars. Its manifestations take various forms: eruptions, dark spots, large-scale structures (coronal loops or prominences). In the case of stars, recent photometric measurements enable detection of the signature of dark spots to the star surface , a priori similar to sunspots. But the variety (in age, mass) of stars gives a scale of these signatrures which vary widely from one star to another, enabling us to draw the landscape of stellar magnetism, thus puting our star among others and to help understanding its magnetism and its variations (11 years cycle for example in the case of Sun).