Thesis topic: Testing disc evolution around intermediate mass stars

Thesis Supervisors: Mario van den Ancker and Monika Petr-Gotzens

Abstract

Two key architectures of planetary systems involving giant exoplanets exist: those with giant planets very close to their star, and those with giant planets beyond the Earth-orbit distance from their parent star. Intermediate-mass stars (1.5-3 solar masses) are most likely homes to the latter systems, i.e. to those planetary systems similar to our own. It is likely that this architecture difference has its origin in a different evolution of dics around intermediate-mass stars versus discs around solar mass stars. FUV-driven disc photoevaporation in intermediate-mass stars versus X-ray driven photoevaporation for low-mass stars is a likely culprit, but so far comprehensive studies of this effect in young stars comprising large samples of young intermediate-mass stars have been lacking.

The PhD student will analyze the above questions using a new sample of around 250 nearby young stars which have recently been observed using the XSHOOTER instrument at the VLT. The project aims to investigate the nature of planet-forming regions around these intermediate-mass stars, via studying the accretion of gas from these regions onto the stellar surface. Accretion can cease as a consequence of a giant planet blocking the flow of gas past its orbit, or when the star-feeding disc of gas is fully consumed. On the other hand, strong accretion seems to suggest a massive gas disc still being present and the material continuing to flow onto the star. With the large sample the project will allow to tackle general questions about how accretion around intermediate-mass stars evolves, and to firmly confirm or reject the hypothesis that disc dispersion in intermediate-mass young stars is driven by different processes compared to the lower-mass stars, offering a natural explanation for the observed diversity of their exoplanetary systems.