PI: Tiago J. L. C. E. Campante

The 20th century has established the field of stellar physics as one of the most advanced within astrophysics. With the advent of very precise space photometry and high-resolution spectroscopy for other stars, the inadequacies of stellar physics have been amplified to show how far we still are from understanding stars and the physics driving these. We are now truly using stars to learn new physics and to revise the simplistic view we had about stellar evolution, from the initial formation up to advanced stages of stellar evolution. These issues and questions provide the motivation and strategy that supports the research pursued under the thematic line on stars at IA.

The objectives of this thematic line aim at consolidating the group's scientific expertise around key theoretical, modeling and observational topics of fundamental importance for future developments in stellar and planetary research. The ongoing activity covers several aspects connected with stellar physics, including observations and modeling work, covering most phases of evolution for stars with a wide range of properties. The focus of our efforts may be grouped in the following two themes:

Characterising stars and stellar systems

• High precision spectroscopy is used to characterise disk emission and star-disk interaction, together with mass accretion and mass loss in young stellar systems and in star forming regions.
• We develop, test and apply tools for extracting fundamental atmospheric parameters of stars from spectroscopic data. Such tools, as well as tools for deriving asteroseismic observables from photometric and spectroscopic time-series, are applied to vast datasets. These tools are being extended to cover young stellar objects, stars with high rotation, very cool stars (M dwarfs) and brown dwarfs.
• We develop/improve data analyses tools to identify activity related to pulsation frequency variations as well as variations of other stellar activity proxies. These tools are applied to ground- and space-based spectroscopic time-series.

Exploring new stellar physics

• Spectroscopic data on a large sample of young stellar objects in different phases of star/disk evolution, are used to study and revise the modeling of accretion of gas onto the central star, outflows through winds and jets, and the photo-evaporation driven by the central source or external stars. We also use diagnostic lines to constrain MHD simulations and models of jets and winds in YSO.
• For a diversity of stellar properties, we measure mass, age, metallicity and helium abundance, depths of convective and He ionization regions as well as properties of the stellar cores. These constraints are then used to test, validate and improve the existing models and the input physics relevant for the evolution of the stars and its interaction with the circum-stellar environment, including planets.
• We develop, test and apply seismic inference tools aimed at retrieving information on chemical mixing and segregation in order to test new formulations being implemented in evolution models. Convection is a key ingredient in the physics of low mass stars that requires new insights and constraints in order to reproduce observed behaviors.
• We are also involved in measuring and study stellar rotation and magnetic fields in stars, both with asteroseismology and spectroscopy, in order to characterise stellar cycles and its driving mechanisms. This is a necessary step to test and improve existing models used to model stellar, and also solar, activity.