scholarly journals Test of a New Theory for Stellar Convection using Helioseismology

1993 ◽  
Vol 137 ◽  
pp. 63-65
Author(s):  
L. Paternó ◽  
R. Ventura ◽  
V.M. Canuto ◽  
I. Mazzitelli
Keyword(s):  
Reaction Rates ◽  
Turbulent Convection ◽  
Standard Theory ◽  
Evolutionary Models ◽  
Mixing Length ◽  
Surface Layers ◽  
Stellar Convection ◽  
The Standard Model ◽  
Convection Model ◽  
Mixing Length Theory

AbstractTwo evolutionary models of the Sun have been tested using helioseismological data. The two models use the same input micro-physics (nuclear reaction rates, opacity, equation of state) and the same numerical evolutionary code, but differ in the treatment of turbulent convection. The first model employs the standard mixing - length theory of convection, while the second one employs a new turbulent convection model which overcomes some basic inconsistencies of the standard theory of convection.The test rests on the calculation of p-mode eigenfrequencies and on the comparison with the helioseismological data.The comparison shows an overall improvement of the eigenfrequencies calculated with the new model with respect to those calculated with the standard model, although it appears that both models still suffer from inaccuracies especially in the treatment of the surface layers.

scholarly journals Turbulent Convection: A New Model

1991 ◽  
Vol 130 ◽  
pp. 27-32
Author(s):  
V. M. Canuto
Keyword(s):  
Observational Data ◽  
Turbulent Convection ◽  
Mixing Length ◽  
Convective Flux ◽  
New Model ◽  
Mixing Length Theory

AbstractWe use the latest models of turbulence to compute a new expression for the turbulent convective flux, Fc. The new values of Fc are up to ten times larger than those given by the mixing length theory, MLT. Astrophysical considerations indicate that the new model fares better with observational data than the MLT.

scholarly journals A Model for Stellar Convection and Spectral Line Asymmetries

1990 ◽  
Vol 138 ◽  
pp. 417-420
Author(s):  
H. M. Antia
Keyword(s):  
Spectral Line ◽  
Stellar Disk ◽  
Doppler Velocity ◽  
Mixing Length ◽  
Linear Superposition ◽  
Convective Flux ◽  
Stellar Convection ◽  
Stellar Velocity ◽  
Intensity Fluctuations ◽  
Mixing Length Theory

A model for stellar convection zones based on linear convective modes using a nonlocal mixing length theory is developed to study the spectral line asymmetries and the line shifts resulting from convective motions in the stellar photospheric region. The amplitudes of these linear convective modes is estimated by requiring the convective flux due to a linear superposition of such modes to reproduce the convective flux in the mixing length model. To study the spectral line asymmetries the convective mode with the largest amplitude in the photospheric line formation region is chosen to represent the stellar velocity field and the accompanying intensity fluctuations. Synthetic spectral line profiles are obtained by summing locally symmetric profiles over the stellar disk according to the local Doppler velocity and intensity fluctuations. The resulting line bisector shapes and the line shifts are compared with observations for α-Cen B. It is found that while the simple model proposed here can explain either the line shifts or the line bisector shape reasonably well, it fails to explain both these characteristics simultaneously.

scholarly journals Viscosity, Thermal and Electrical Conductivities in Turbulent Convection

1981 ◽  
Vol 93 ◽  
pp. 280-280
Author(s):  
Wasaburo Unno ◽  
Tohru Nakano ◽  
Masa-aki Kondo
Keyword(s):  
Spectral Theory ◽  
Convection Zone ◽  
Turbulent Convection ◽  
Nonlinear Interactions ◽  
Mixing Length ◽  
Average Life ◽  
Representative Element ◽  
Stellar Convection ◽  
Electrical Conductivities

Turbulent diffusivities are often used for representing nonlinear interactions of turbulent elements on the motion of a larger scale. In turbulent convection, the average life of a representative element is substantially lengthened by bouyancy. Taking this effect into account, we calculate turbulent viscosities, thermal and electrical conductivities for Boussinesq fluids on the basis of a spectral theory of turbulent convection (Nakano, Fukushima, Unno, and Kondo, 1979). The effect of bouyancy results in the increase of turbulent diffusivities, compared with the case without bouyancy. We also propose the generalization of the method such that a stellar convection zone can be theoretically constructed without recourse to the mixing length.

scholarly journals Pre-main Sequence models with convection described by 2D-RHD numerical simulations

2006 ◽  
Vol 2 (S239) ◽  
pp. 320-322
Author(s):  
Josefina Montalbán ◽  
Francesca D'Antona
Keyword(s):  
Boundary Conditions ◽  
Main Sequence ◽  
Open Clusters ◽  
Mixing Length ◽  
Parameter Calibration ◽  
Full Spectrum ◽  
Hydrodynamical Models ◽  
Convection Model ◽  
Lithium Depletion ◽  
Mixing Length Theory

AbstractThe Teff location of Pre-Main Sequence (PMS) evolutionary tracks depends on the treatment of over-adiabaticity. We present here the PMS evolutionary tracks computed by using the mixing length theory of convection (MLT) in which the αMLT = l/Hp parameter calibration is based on 2D–hydrodynamical models (Ludwig et al. 1999). These MLT–α2D stellar models and tracks are very similar to those computed with non–grey ATLAS9 atmospheric boundary conditions and Full Spectrum of Turbulence (FST) convection model both in the atmosphere and in the interior. As for the FST models, the comparison of the new tracks with the location on the HR diagram of pre–MS binaries is not completely satisfactory; and the pre–MS lithium depletion in the MLT–α2D tracks is still much larger than that expected from the observations of lithium in young open clusters. Thus, in spite of the fact that 2D RHD models should provide a better convection description than any local model, their introduction is not sufficient to reconcile theory and observations. Lithium depletion in young clusters points towards a convection efficiency which, in pre–MS, should be smaller than in the MS.

ABUNDANCE ANOMALIES PRODUCED BY NUCLEAR REACTIONS IN STELLAR SURFACE LAYERS: I. NUCLEAR-REACTION RATES

1967 ◽  
Vol 45 (10) ◽  
pp. 3275-3296 ◽  
Author(s):  
P. J. Brancazio ◽  
A. Gilbert ◽  
A. G. W. Cameron
Keyword(s):  
Statistical Theory ◽  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Level Density ◽  
Preliminary Investigation ◽  
Computer Time ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Surface Layers

A preliminary investigation of the effects on abundances in stellar surfaces of extensive nuclear bombardment required the calculation of more than 105 nuclear-reaction cross sections. It was necessary to develop simplified methods for using the statistical theory of nuclear reactions to make these calculations in order that the computer time should not be prohibitive. These methods are described here and the results are compared with experiment. The accuracy of the calculations is, in general, about as good as, or somewhat better than, that obtained in previous applications of the statistical theory, probably because the use of an accurate level density formula outweighed the crudity of other approximations.

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