Basic Properties of Anisotropic Stellar Wind Expansion in the Fluid Approach

International audienceIn the solar wind, which is the prototype of stellar wind, two kinds of particle temperature anisotropy are observed. The proton temperature perpendicular to the interplanetary magnetic field (IMF) is larger than the parallel temperature in coronal holes at the origin of the fast solar wind. This anisotropy can be very large for atomic oxygen ions. This phenomenon is associated to wave-particle interactions. However, it is known that without any particle interaction, the opposite type of temperature anisotropy should develop in the expansion. This is probably the case in the slow solar wind source regions. In both cases, the electron seem to be rather isotropic in the corona but for less collisional medium the anisotropy should increase. This presentation is devoted to an analysis of dynamical properties of stellar atmosphere in the presence of the two kinds of temperature/pressure anisotropy. We choose to consider the one fluid approach in order to focus on the basic properties. The hydrostatic equilibrium conditions, the transcritical solution properties, the expansion velocity and the mass loss rate are analyzed for anisotropic isothermal and non-isothermal atmospheres. The extension of such analysis to two fluid models and multimoment models established for weakly collisional stellar winds are discussed