Today we will learn about single-star physics in evolved massive stars. Even if many of these stars are born in binary systems, we must understand their intrinsic physics in order to predict their observational signatures and understand their internal structure. 

Today we focus on the outer structure of these stars, in particular, the often-vigorously-convective H-rich envelope, after the H-burning Main Sequence. This structure is very important for a few reasons: For one, it is the surface properties of these stars which we actually see in observations. Second, the outer structure and its response determines how it interacts with any stellar companions. Third, while core properties determine the explosion energy and compact remnant, it is the star's envelope which mediates the observed Supernova emission! 

It's worth noting that this lab does not exist in isolation. The 2022 MESA Summer School Friday Session lab materials, for example, focused on nuclear reactions and advanced-stages of burning relevant for setting the core structure of massive stars at core-collapse -- this is extremely important for understanding the core-collapse explosion mechanism (explosions which were explored in some detail in the 2015 MESA Summer School's Tuesday/Wednesday labs). Moreover, the Monday/Tuesday lab materials for the 2014 MESA Summer School focused on winds and super-Eddington evolved massive star envelopes, in the context of enhanced pre-supernova mass loss. Complementarily, the Tuesday lab of the 2016 MESA Summer School focused on envelope inflation during the H-burning Main Sequence and dynamical pulsations in the super-Eddington layers. And for lovers of stellar multiplicity, this upcoming Thursday's lab for MESA Down Under will focus on Massive Star Binaries and mass-transfer in these systems, as did the Friday lab of the 2023 MESA Summer School at Konkoly, the final lab sessions of the 2021 [Online] MESA Summer School, and many others. 

This MESA Lab is divided into three minilabs driven by different concepts relevant to the physics of massive stars, with focuses on different aspects of the MESA code. We hope you will enjoy the lab and gain useful theoretical and technical background for your future MESA endeavors. Good luck!