Abstract
ABSTRACT 3D hydrodynamics models of deep stellar convection exhibit turbulent entrainment at the convective-radiative boundary which follows the entrainment law, varying with boundary penetrability. We implement the entrainment law in the 1D Geneva stellar evolution code. We then calculate models between 1.5 and 60 M⊙ at solar metallicity (Z = 0.014) and compare them to previous generations of models and observations on the main sequence. The boundary penetrability, quantified by the bulk Richardson number, RiB, varies with mass and to a smaller extent with time. The variation of RiB with mass is due to the mass dependence of typical convective velocities in the core and hence the luminosity of the star. The chemical gradient above the convective core dominates the variation of RiB with time. An entrainment law method can therefore explain the apparent mass dependence of convective boundary mixing through RiB. New models including entrainment can better reproduce the mass dependence of the main-sequence width using entrainment law parameters A ∼ 2 × 10−4 and n = 1. We compare these empirically constrained values to the results of 3D hydrodynamics simulations and discuss implications.
Highlights
It has long been known that convective boundary mixing (CBM) must be included into stellar models in order to reproduce observations
This leads to an increase in lc∆b, which is strongest at the very beginning of the main sequence since there is no chemical composition gradient to start with
We have calculated a grid of 1D stellar models using the Geneva stellar evolution code with masses between 1.5 and 60 M and at solar metallicity (Z = 0.014)
Summary
It has long been known that convective boundary mixing (CBM) must be included into stellar models in order to reproduce observations. The main sequence (MS) width of clusters is one of the best-known examples of such observations; other examples include large samples of wide binaries and asteroseismic measurements G. Claret & Torres 2019; Deheuvels et al 2016). Stellar models’ CBM schemes are calibrated to give results consistent with the observed reality. Castro et al (2014) showed that current generations of models have MS widths on the HertzsprungRussell diagram (HRD) which are too narrow for high mass stars. The discrepancy in width grows larger with mass
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