The Propagation of Internal Gravity Waves Through Stellar Convection Zones

Stars play a pivotal role in our universe by producing most of the heavy elements via nuclear fusion and releasing them into the interstellar medium (ISM) during their later stages of evolution via stellar winds or supernovae, therefore

contributing to galactic chemical enrichment. Additionally, the ionizing radiation of young stars helps to regulate star formation via stellar feedback and upon reaching the final stages of their lives, more massive stars may be involved in the production of gravitational waves recently detected by LIGO as neutron stars or black holes.

The recent advent of space telescopes such as Kepler, TESS and CoRoT have provided observers and asteroseismolo-gists with spectroscopic and photometric data for a much larger range of stars than ever before, resulting in a variety

of new studies reporting observational evidence for the detection of internal gravity waves (IGW) and standing gravity wave (g-mode) pulsations in massive stars. These buoyancy oscillations are observed both in stellar interiors and

earth's atmosphere, where they are generated by vertical disturbances in stably stratified fluids (a fluid with density variation arranged in layers). In stars they are generated at convective radiative boundaries (CRBs), where vertical

columns of fluid can penetrate through the boundary and disturb material in the radiative region, which alongside Reynolds stresses in the form of eddies, is conducive to the generation of IGW. In stars with convective cores these

waves then propagate outward through the radiative region where their amplitudes grow due to decreasing density, transporting angular momentum and energy as they travel, as well as contributing to the mixing of chemicals. As

they draw closer to the surface these waves can then break, transferring their energy to turbulent motions which can further contribute to chemical mixing and enrichment near the surface.

However, some intermediate and massive stars possess subsurface convection zones as a result of an opacity bump in the star caused by iron group elements (the iron opacity bump) or helium (the helium bump), which may alter the

properties of these waves if they can penetrate through them alongside their potential observable signatures at the surface. It is then imperative to build an understanding of how these regions could alter propagating IGW and standing

gravity waves (g-modes) for observers to identify their signatures in stars with subsurface convection regions and be able to form a clearer idea of their internal structure and dynamics. This project intends to address this problem by

utilising 2D hydrodynamic simulations on a cylindrical polar grid to simulate the propagation of IGW through an intermediate convection zone of a given thickness and position within the star and studying their transmission and properties, alongside how these change when altering the thickness and position of the intermediate convective region.

When combined with observational results, this knowledge could be used to identify the signatures of IGW in these stars, thereby potentially indicating enhancements to angular momentum transport and chemical mixing which could then influence stellar models. The signatures of IGW could also be used to study the interior structure and dynamics

of the star such as rotation and depth of the convection zone.