Low to intermediate mass stars, as for example the Sun, evolve towards the asymptotic branch of giants (AGBs), showing increased mass loss during their evolution. AGBs are crucial contributors to the chemical enrichment of galaxies because they lose huge amounts of their mass. 

These stars are characterized by:

• large-amplitude variations in radius, brightness, and surface temperature; and

• a high rate of mass loss due to an interaction between pulsation, dust formation, and radiative pressure on the surface.

Their complex dynamics affect measurements and amplify uncertainties on their stellar parameters. Their surfaces are covered by a few large convective cells (with a long life span). These are supported by smaller-scale structures with a shorter duration. The atmosphere above the surface is made up of shock waves, that are produced inside the star and shaped by the top of the convection zone, when these shock waves travel outward. In the presence of light asymmetries, the position of the photocentre does not coincide with the barycentre of the star and changes as the convective pattern changes over time.

The displacement of the photocentre can be explained by numerical simulation, suggesting that the variability related to stellar convection largely explains the Gaia parallax uncertainties. Consequently, parallax variations on Gaia's measurements could be used to extract the fundamental parameters of these stars. With future releases of Gaia, more precise parallax measurements will become available which will hopefully improve these characterisations even further.

The ESO workshop "Ground-Based Thermal Infrared Astronomy – Past, Present and Future" was held on-line from October 12-16, 2020. Originally planned as a traditional in-person meeting at ESO in Garching during April 2020, it was rescheduled and transformed into a fully on-line event due to the COVID-19 pandemic. With 337 participants from 36 countries the workshop was a resounding success, demonstrating the wide interest of the astronomical community in the science goals and toolkit of ground-based thermal infrared astronomy. In this informal discussion we will report on the organization of the workshop and will present some of the science highlights.