New Theory of Stellar Convection without the mixing-length parameter: new stellar atmosphere models

Stellar convection is customarily described by the mixing-length theory, which makes use of the mixing-length scale to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is taken to be proportional to the local pres...

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Bibliographic Details
Published in:Proceedings of the International Astronomical Union 2015-08, Vol.11 (A29B), p.154-155
Main Authors: Pasetto, Stefano, Chiosi, Cesare, Cropper, Mark
Format: Article
Language:English
Subjects:
Astrophysics
Atmosphere
Contributed Papers
Mathematical analysis
Mathematical models
Navier-Stokes equations
Parameters
Star & galaxy formation
Stars & galaxies
Stellar atmospheres
Stellar convection
Sun
Time dependence
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Summary:Stellar convection is customarily described by the mixing-length theory, which makes use of the mixing-length scale to express the convective flux, velocity, and temperature gradients of the convective elements and stellar medium. The mixing-length scale is taken to be proportional to the local pressure scale height, and the proportionality factor (the mixing-length parameter) must be determined by comparing the stellar models to some calibrator, usually the Sun. No strong arguments exist to suggest that the mixing-length parameter is the same in all stars and all evolutionary phases. Because of this, all stellar models in the literature are hampered by this basic uncertainty. In a recent paper (Pasetto et al. 2014) we presented a new theory that does not require the mixing length parameter. Our self-consistent analytical formulation of stellar convection determines all the properties of stellar convection as a function of the physical behavior of the convective elements themselves and the surrounding medium. The new theory of stellar convection is formulated starting from a conventional solution of the Navier-Stokes/Euler equations, i.e. the Bernoulli equation for a perfect fluid, but expressed in a non-inertial reference frame co-moving with the convective elements. In our formalism, the motion of stellar convective cells inside convective-unstable layers is fully determined by a new system of equations for convection in a non-local and time-dependent formalism. We obtained an analytical, non-local, time-dependent solution for the convective energy transport that does not depend on any free parameter. The predictions of the new theory are compared with those from the standard mixing-length paradigm with positive results for atmosphere models of the Sun and all the stars in the Hertzsprung-Russell diagram.
ISSN:1743-9213
1743-9221
DOI:10.1017/S1743921316004671