Letters of Intent received in 2019

LoI 2021-2057
Winds from close-in exoplanets to massive stars

Topics

1) Winds from close-in planets to massive stars
• wind acceleration mechanisms
• magnetic fields as a common denominator [wind driver and wind channeling]
• role of clumping in shaping the wind flow

2) Relevance of winds on stellar/planetary evolution
• angular momentum and wind coupling: angular-momentum losses in cool dwarfs and exoplanets, rotation—mass-loss connection in early-type stars
• winds in the evolution of massive stars and connection to supernova progenitors
• impact of planetary winds on atmospheric evolution and exoplanet demographics

3) Flow-flow interactions:
• winds-ISM interaction: Astrospheres around low-mass stars
• winds-ISM interaction: wind bubbles and massive runaway stars
• colliding winds in massive binaries
• flow-flow interaction in close-in exoplanets and host-stars

Rationale

Winds form an integral part of Astronomy - from regulating rotation of stars through enriching galaxies with fresh materials, 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 exoplanets, winds take the form of atmospheric escape, which affects their atmospheric evolution. Winds of highly irradiated exoplanets have now been directly observed in several close-in exoplanets and are indirectly detected in the observed exoplanet radius distributions.

In recent years, several observing programmes and space missions have focused on studying winds from stars and exoplanets. The HST director has committed 1000 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 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 have 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.

These very same surveys are also used for exoplanet detection. Missions like Kepler, TESS and Plato (will) provide the statistics for planet population study and hence infer the indirect presence of planetary winds in shaping the distribution of sizes of close-in exoplanets. HST has been fundamental also in detecting planetary winds 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 window has been confirmed to Dec 2020). Recent observations have also opened the possibility to detect planetary winds from the ground.

With all the synergy between these different communities, we therefore wish to bring together researchers on winds of close-in exoplanets and of stars, from both the high and low-mass stars community, in order to gain insight in the physics and the modelling tools used by these communities. An IAU symposium will be an ideal site for fostering communication and leap advances in the field. Additionally, an IAU Symposium specific to “winds” has never taken place before, let alone on the synergy between exoplanetary winds and stellar winds.

In addition to the experts in the area, the topic also appeals to attendees with a broader range of interests, such as stellar evolution, magnetic fields, convection, pulsations, rotation, radiative pressure, exoplanets, galactic chemical evolution, as well as the interaction with the interstellar medium. The General Assembly is, thus, the ideal place to hold such a meeting. We expect that attendees who would normally not attend a one-week long meeting on “winds”, would nevertheless participate in our symposium, as they would be present during the GA.

Over the next few weeks, we are planning to form a geographically balanced and diverse SOC to optimise the input from the relevant communities.