Sumill

Sumill refers to a phenomenon where a star undergoes a partial or complete inversion of its convection zone. This process is primarily observed in certain types of stars, particularly red giants and asymptotic giant branch (AGB) stars. During a sumill event, cooler, denser material from the star's outer atmosphere sinks inwards, while hotter, less dense material from the interior rises to the surface.

This internal mixing can have significant observable consequences. It can lead to changes in the star's surface composition, bringing elements that were synthesized deeper within the star to the visible layers. For instance, elements like carbon or s-process elements might become more abundant at the surface. Sumill events can also affect a star's luminosity and temperature, causing them to shift on the Hertzsprung-Russell diagram.

The precise mechanisms driving sumill are still an active area of research in stellar astrophysics. It is thought to be related to specific thermal instabilities or convective overshoot processes occurring within the star's complex internal structure. Understanding sumill is crucial for accurately modeling stellar evolution and for interpreting observations of evolved stars, which play a vital role in galactic chemical enrichment. The frequency and impact of sumill events can vary depending on the star's mass and evolutionary stage.