Prominences as tracers of coronal structure and mass loss in cool stars

07/04/2021 - 14:00 - 15:00
Remoto, com transmissão pela internet
Prominences as tracers of coronal structure and mass loss in cool stars
Moira Jardine
University of St. Andrews
In this era of exoplanet detection and characterisation, it has become even more important to understand stars as planet hosts. In particular, we need to understand the impact of stellar magnetic activity on the local environment within which exoplanets form and evolve. Spectropolarimetric techniques now allow us to map stellar magnetic fields across the surfaces of stars. In addition, we can map the surface distribution of the helicity density of these magnetic fields. These observations have challenged our understanding of how stellar magnetic fields are generated and how they evolve. We cannot, however, observe these fields in the corona, to determine the sources of the stellar wind, or the distribution of X-ray bright regions. This structure can be revealed, however, by the observation of stellar prominences in young, rapidly-rotating solar-like stars. These cool condensations are centrifugally supported and were dubbed "slingshot prominences" when they were discovered in the 1980's. Their observational signatures - travelling absorption features in H-alpha  - reveal the locations of the closed magnetic loops that support them. Comparison between observed and synthetic H-alpha dynamic spectra produced using observed stellar magnetograms have the power to test field extrapolation techniques and to determine the mass and angular momentum losses produced by their ejection. Recent results also demonstrate that for the most active stars, prominence masses and lifetimes can reveal the mass loss rates in the stellar wind - something that is difficult to do by other methods.
Moira Mary Jardine is a British astrophysicist with interest in young stars, particularly the structure of their magnetic fields and coronae, and the mechanisms by which they interact with their disks and planets. In 2012 she became the first female Professor of Physics at the University of St Andrews.