The Impact of the Hydrodynamic Instabilities on Stellar Evolution.

Abstract

The behaviour of convection within stellar interiors is turbulent and remains an ill- constrained factor within stellar models, despite advancements in computational mod- elling and astroseismic measurements. The impact of overshooting on the evolution of stellar structures is well known, but despite many proposals for its formulation, there is still no universal agreement to its application. This investigation attempts to better con- strain and improve upon the formulation of overshooting and related physical phenom- ena for 8-30𝑀⊙ massive stars and the solar interior. Observational constraints for double eclipsing binary systems and main sequence stars derived from stellar population den- sity maps were used to fit stellar models with 0.1 ≤ 𝛼ov ≤ 0.5. Stellar structure data was extracted from models constrained by observations, and used to construct variable over- shooting relationships to provide evolving values of 𝛼ov during the MS. It was found that logarithmic or power-law relationships between 𝛼ov and either 𝐿 or 𝑀co were the most suited to reproduce the MS band coverage predicted by models between 8-20𝑀⊙. The im- pact of local heating below the solar convective zone boundary was implemented as ∇𝑇 modification in 1D solar models. These modifications were able to reproduce the sound- speed profile reported for helioseismic measurements, which standard solar models were found to have discrepancies to.