Winds form an integral part of astronomy - from regulating rotation of stars through enriching galaxies with fresh materials, outflowing winds persist during the entire lives of stars and play a key role in shaping the observed exoplanet demographics. In the case of massive stars, their winds are a vital ingredient of their evolution, from the main sequence to the pre-supernova stage, determining black hole masses as measured from gravitational waves. In the case of low-mass stars, their winds dictate rotational evolution, which affect angular momentum distribution within the stellar interior and thus affect generation of magnetic fields. Finally, in the case of planets, winds take the form of atmospheric escape, which can strongly affect their atmospheric evolution. Strong escape of highly irradiated exoplanets have now been observed in several close-in exoplanets during transits and are indirectly detected in the observed exoplanet radius distribution.
Although the only astrophysical wind that we are able to directly probe is that of the Sun, the past decades have seen great progress in observing winds of other astrophysical objects. In particular, in recent years, several observing programmes and space missions have focused on studying winds from our Sun, other stars and exoplanets.
On the solar side, two new space missions, Parker Solar Probe and Solar Orbiter, are dedicated to studying the physics of the solar wind. By traveling much closer to the Sun than any other spacecraft has ever been, these new missions will allow direct measurements of the solar wind at an unprecedented close distance, giving us more information of the acceleration mechanism that drives the solar wind. Data from these missions might provide interesting implications for the variability of the plasma environment at the orbits of close-in exoplanets. On the stellar side, the HST director has committed 1,000 Hubble orbits on ULLYSES, the "Ultraviolet Legacy Library of Young Stars as Essential Standards", providing the key motivator to understanding the winds of massive OB stars and low-mass stars at the same time. Massive stars ubiquitously show discrete absorption components in their ultraviolet spectra, the origin of which is still an open question. One of the possible candidates for these absorption lines are hot spots from magnetic fields originating from the sub-surface convection zone that has more recently been revealed. To make theoretical progress in this area, physical insight from the low-mass stars community is particularly welcome.
Winds of low-mass stars are magnetically driven, and magnetism has been either directly (through Zeeman effects) or indirectly (through activity proxies) observed in these stars. Recently, circular spectropolarimetry surveys (MiMeS and BOB) detected many new magnetospheres around massive stars, similarly to what has been seen in low-mass counterparts. In spite of similarities, there is a major difference between winds of low- and high-mass stars: their mass-loss rates are orders of magnitude different, due to different physical processes driving their winds. Even with substantially lower mass loss rates, winds of low mass-stars play a fundamental role in removing angular momentum, and thus, shaping the rotational evolution of these stars. Monitoring surveys, like Kepler and TESS, have measured rotation rates of low-mass stars and are thus key for constraining their wind evolution. GAIA is currently revolutionising the field by providing the largest dataset of stellar rotational periods, which will inform stellar wind models. On the planetary side, missions like Kepler, TESS and Plato (will) provide the statistics for planet population studies and hence infer the indirect presence of outflowing planetary winds in shaping the distribution of sizes of close-in exoplanets. HST has been fundamental in detecting strong atmospheric escape of close-in giant planets through ultraviolet transmission spectroscopy, and NASA is funding CUTE, a CubeSat mission fully dedicated to study the intense mass loss of exoplanets (launch confirmed for Dec 2020). Recent observations have also opened the possibility to detect escaping planetary winds from the ground, for example, using the Helium infrared triplet at 10830A.
One critical open question is the theoretical differences of fully (stellar winds) and partly ionised (exoplanet) winds and radiative transfer (with metal lines) in the planetary wind acceleration region. Ionised and partly/mostly neutral flows do not behave in the same way, and the neutral fraction depends critically on the planetary system. In terms of radiative transfer, on the other hand, we have recently started to realise that particularly ultra-hot Jupiters can be much more complicated than simple hydrogen models. Exchange of ideas between the exoplanetary community and the low-mass stars and high-mass stars (radiative transfer) communities can lead to possibly fruitful insights.
With all the synergy between these different communities, we therefore wish to bring together researchers on winds of exoplanets and stars, from both the high and low-mass stars and solar communities, in order to gain insight in the physics and modelling tools used by these communities. An IAU symposium will be an ideal site for fostering communication and opportunities for major advances in the respective fields.
The programme of talks will be updated in due course. The deadline for abstract submission is 31 March 2022. Please, register and submit your abstract through the IAUGA website.