Stars like the Sun possess a thermal wind that shapes their surrounding, the so-called astrosphere. Solar-like winds are also ubiquitous in cool stars, and the angular momentum loss that they induce has broad astrophysical consequences. The large range of stellar convective properties and rotation rates also permits sensitive tests of the underlying solar wind and dynamo models. Thanks to in situ (SoHO, ACE satellites) and out-of-the ecliptic measurements (Ulysses satellite), and probing of the heliopause (Voyager I & II, IBEX), we are starting to have a better understanding of the solar wind and its heliosphere. However, key questions still remain unanswered. For example, the mechanisms by which the Sun and stars heat and control their coronae and helio/astrospheres is still controversial. Likewise, another uncertainty is the relationship between magnetic field topology and global stellar parameters, such as convective overturn timescale or rotation rate, or the origin of fast and slow wind streams. Moreover, low mass stars spin down as they age, making rotation a possible proxy for determining stellar ages, e.g. through gyrochronology. However, there is interesting recent data suggesting inefficient torques in old stars. This opens up the question about whether there is a global transition in rotational and dynamo states at activity levels close to that of the Sun. It also raises questions about the governing processes for mass and angular momentum loss in low mass stars. We know that there is a feedback loop between all these processes as rotation controls dynamo action and stellar magnetic activity that in turn controls the wind, mass and angular momentum loss and hence stellar spin down.
The goal of our ISSI team is to tackle these questions with state-of-the-art numerical simulations and space data analysis. We will also prepare some of the analysis and modeling tools for the scientific exploitation of the soon to be launched ESA Solar Orbiter and NASA Solar Probe+ space missions, whose main goals are respectively to answer the questions: How does the Sun control its heliosphere and generate its 11-yr cyclic magnetic field? How does the solar wind accelerate and influence its surrounding? Such questions naturally extend to other stars.