Toward a consistent use of overshooting parametrizations in 1D stellar evolution codes

TL;DR

This paper clarifies that overshooting parametrizations in 1D stellar evolution codes correspond to different physical regimes influenced by radiative effects, advocating for their consistent application based on local conditions.

Contribution

It identifies the physical regimes underlying various overshooting parametrizations and proposes their consistent use depending on local radiative conditions in stellar models.

Findings

Three regimes of overshooting based on radiative effects.

Hydrodynamical simulations support the three-regime classification.

Recommendation for context-dependent application of parametrizations.

Abstract

Several parametrizations for overshooting in 1D stellar evolution calculations coexist in the literature. These parametrizations are used somewhat arbitrarily in stellar evolution codes, based on what works best for a given problem, or even for historical reasons related to the development of each code. We bring attention to the fact that these different parametrizations correspond to different physical regimes of overshooting, depending whether the effects of radiation are dominant, marginal, or negligible. Our analysis is based on previously published theoretical results, as well as multidimensional hydrodynamical simulations of stellar convection where the interaction between the convective region and a stably-stratified region is observed. Although the underlying hydrodynamical processes are the same, the outcome of the overshooting process is profoundly affected by radiative effects. Using a simple picture of the scales involved in the overshooting process, we show how three regimes are obtained, depending on the importance of radiative effects. These three regimes correspond to the different behaviors observed in hydrodynamical simulations so far, and to the three types of parametrizations used in 1D codes. We suggest that the existing parametrizations for overshooting should coexist in 1D stellar evolution codes, and should be applied consistently at convective boundaries depending on the local physical conditions.