Theoretical values of convective turnover times and Rossby numbers for solar-like, pre-main sequence stars

TL;DR

This paper provides theoretical estimates of convective turnover times and Rossby numbers for pre-main sequence solar-like stars, exploring their dependence on rotation, convection regimes, and atmospheric models to improve understanding of stellar magnetic activity.

Contribution

It introduces a physically consistent method to calculate convective turnover times and Rossby numbers for rotating pre-main sequence stars using updated stellar models.

Findings

Theoretical values of tau_c, tau_g, and Ro agree qualitatively with previous literature.

Rotation increases tau_g slightly in models.

Non-gray boundary conditions produce smaller tau_g values.

Abstract

Magnetic fields are at the heart of the observed stellar activity in late-type stars, and they are presumably generated by a dynamo mechanism at the interface layer between the radiative and the convective stellar regions. Since dynamo models are based on the interaction between differential rotation and convective motions, the introduction of rotation in the ATON 2.3 stellar code allows for explorations regarding a physically consistent treatment of magnetic effects in stellar structure and evolution, even though there are formidable mathematical and numerical challenges involved. As examples, we present theoretical estimates for both the local (tau_c) and global (tau_g) convective turnover times for rotating pre-main sequence solar-type stars, based on up-to-date input physics for stellar models. Our theoretical predictions are compared with the previous ones available in the literature. In addition, we investigate the dependence of the convective turnover time on convection regimes, the presence of rotation and atmospheric treatment. Those estimates, this quantities can be used to calculate the Rossby number, Ro, which is related to the magnetic activity strength in dynamo theories and, at least for main-sequence stars, shows an observational correlation with stellar activity. More important, they can also contribute for testing stellar models against observations. Our theoretical values of tau_c, tau_g and Ro qualitatively agree with those published by Kim & Demarque (1996). By increasing the convection efficiency, tau_g decreases for a given mass. FST models show still lower values. The presence of rotation shifts tau_g towards slightly higher values when compared with non-rotating models. The use of non-gray boundary conditions in the models yields values of tau_g smaller than in the gray approximation.