Stellar mixing

Abstract

In this paper we use the Reynolds stress models (RSM) to derive algebraic expressions for the following variables: a) heat fluxes; b) μ fluxes; and c) momentum fluxes. These relations, which are fully 3D, include: 1) stable and unstable stratification, represented by the Brunt-Väisäla frequency,; 2) double diffusion, salt-fingers, and semi-convection, represented by the density ratio R μ = ∇ μ (∇ − ∇ ad ) −1 ; 3) shear (differential rotation), represented by the mean squared shear Σ 2 or by the Richardson number, Ri = N 2 Σ −2 ; 4) radiative losses represented by a Peclet number, Pe; 5) a complete analytical solution of the 1D version of the model. In general, the model requires the solution of two differential equations for the eddy kinetic energy K and its rate of dissipation, ε. In the local and stationary cases, when production equals dissipation, the model equations are all algebraic.

CNO abundances and carbon isotope ratios in evolved stars of the open clusters NGC 2324, NGC 2477, and NGC 3960

“…Spectra of NGC 3960 310757 (red line), which has a carbon isotope ratio equal to 10, and spectrum of NGC 3960 310758 (blue line), which has a value of 20. Drazdauskas et al (2016), Mikolaitis et al (2010, 2011a,b, 2012), and Tautvaišienė et al (2000, 2005, crosses for Smiljanic et al (2009), a diamond for Santrich et al (2013), a circle is for Luck (1994), and plus signs for Gilroy (1989). The solid lines represent standard dredge-up models (Eggleton et al 2008;Charbonnel & Lagarde 2010;Lagarde et al 2012)), the dash-dotted line represents the thermohaline mixing model by Eggleton et al (2008), the short-dashed line is for a model including thermohaline mixing Charbonnel & Lagarde (2010), and the long-dashed line represents a model that includes both the thermohaline and rotational effects (Lagarde et al 2012).…”

Shear mixing in stellar radiative zones

“…Lindborg & Brethouwer 2008), and additional assumptions such as closure models (e.g. Canuto 1998Canuto , 2011 are thus required, introducing uncertainties. Although it would be interesting to test such more complex models with numerical simulations, we focus here on Zahn's model, which is commonly used in stellar evolution calculations.…”

Turbulent Convection in Stellar Interiors. Iii. Mean-Field Analysis and Stratification Effects

“…Reynolds-Averaged Navier-Stokes (RANS) equations are a promising framework for this. Much effort has been already devoted to RANS in the context of stellar hydrodynamics, see, e.g., Canuto (1997Canuto ( , 2011, Xiong et al (1997), Canuto & Dubovikov (1998), Deng et al (2006), and references therein. We adopt the same methodology.…”