Stellar rotation and magnetism in the era of ultra-precise space-based photometry


Principal Investigator: Ângela Santos


Fundação para a Ciência e a Tecnologia

Stellar brightness variations result from the contribution of different stellar phenomena at different timescales. For solar-type stars, at long timescales the brightness variations are dominated by magnetic activity, rotation, and emergence/decay of active regions. Granulation, which is related to convection and surface gravity, becomes important at intermediate timescales. At short timescales, brightness variations are caused by acoustic oscillations, which depend on stellar structure and dynamics, being sensitive to magnetic activity. Ultra-precise photometry allows to study such brightness variations, providing a unique opportunity to characterize stellar properties. This project is centered on the analysis of Kepler, K2, and TESS photometric data for solar-type stars (stars of spectral type from late F to M). It consists of a comprehensive study of stellar brightness variations at long and short timescales with a focus on stellar magnetic and rotation properties. I will investigate the spot modulation of light curves to measure average surface rotation, latitudinal differential rotation, active-region lifetimes, and photometric activity. Having such properties for a large sample of solar-type stars will allow studying how they depend on each other and on other stellar properties, such as effective temperature, age, and metallicity. This will impact our understanding of stellar and solar magnetism. The long-term Kepler photometry further allows studying temporal changes in photometric activity. I will investigate photometric variability, in particular, to search for magnetic activity cycles. Moreover, by studying temporal variations of the seismic properties of solar-type stars, asteroseismology allows detecting and characterizing magnetic cycles. In this project, I will analyze TESS data to revisit the acoustic frequencies of targets observed previously by Kepler, searching for activity-related frequency variations. Depending on the observation strategy of the TESS extended mission, this analysis can be expanded to other targets. The results from this project will improve our understanding of the evolution of magnetic activity and rotation, which in turn impact stellar evolution itself. Consequently, this project will also impact Galactic archaeology, as a proper understanding of activity and rotation evolution will allow for accurate age estimates, which are particularly important for non-seismic targets. Magnetic activity and rotation are also important properties for exoplanet research, as their signal hampers the detection of planetary signals and magnetic activity affects space weather and the habitability of planets. This project will also impact the future ESA photometric space-based mission PLATO.