Why is the precise boundary of the convective zone critical input for stellar evolution codes?
It determines how much of the star's interior chemically mixes with fresh hydrogen fuel
The boundary between the radiative zone and the convective zone dictates the extent of material mixing over the star's main-sequence lifetime. In solar-type stars, the inner radiative zone accumulates inert helium ash while remaining chemically isolated from the outer convective shell containing fresh hydrogen fuel. If the boundary were calculated incorrectly, stellar evolution models would fail to accurately predict when the core runs out of fuel or how the star expands during its red giant phase. For completely convective low-mass stars, this boundary determines that nearly all fuel is utilized, resulting in vastly different predicted lifespans compared to stars where mixing is restricted.
