scholarly journals Convectively Generated Turbulent Pressure: A Possible Cause for η Car - Type Shell Ejections

1991 ◽  
Vol 143 ◽  
pp. 549-549
Author(s):  
M. Kiriakidis ◽  
N. Langer ◽  
K.J. Fricke
Keyword(s):  
Massive Star ◽  
Energy Transport ◽  
Convection Zone ◽  
Hydrostatic Equilibrium ◽  
Convective Zone ◽  
Contraction Phase ◽  
Hydrodynamic Calculation ◽  
Turbulent Pressure ◽  
Possible Cause ◽  
Η Car

A selfconsistent hydrodynamic calculation of a very massive star (MZAMS = 2OOM⊙) including turbulent pressure and energy has been performed. In the contraction phase after core hydrogen exhaustion, the star moves towards cool surface temperatures in the HR diagram (cf. Fig. 1). Consequently, (at Teff ⋍ 8000K) an envelope convection zone developes, and its inner boundery moves inwards with time. First, the envelope remains in hydrostatic equilibrium, with radiation pressure correspondingly decreasing as turbulent pressure increases (gas pressure is small). However, due to the fact, that the gradient of the turbulent pressure is directed inwards at the bottom of the convective zone, this part of the star rapidly contracts. Due to the released contraction energy, the luminosity locally exceeds the Eddington-luminosity. It cannot be transported outwards by convection in the upper part of the convection zone, where convective energy transport is inefficient (▽c ⋍ ▽r) . Thus, the local super-Eddington luminosity leads to the ejection of the overlying layers.

scholarly journals Internal Structure

1995 ◽  
Vol 10 ◽  
pp. 323-326
Author(s):  
J. Christensen-Dalsgaard
Keyword(s):  
Stellar Evolution ◽  
Energy Transport ◽  
Molecular Diffusion ◽  
Convection Zone ◽  
Reaction Rates ◽  
Spherically Symmetric ◽  
Turbulent Pressure ◽  
Simplifying Assumptions ◽  
Effects Of Rotation ◽  
Hydrostatic Balance

In this section I concentrate on the spherically symmetric aspects of solar structure, corresponding to “classical” stellar evolution models. Such models are characterized by a number of simplifying assumptions, as well as by the physical properties of matter in the star, conveniently labeled “micro-physics”. The latter include descriptions of the equation of state, the opacity and the nuclear reaction rates; in addition, molecular diffusion, included in several recent calculations, should be considered as part of the micro-physics. The assumptions in the standard calculations, simplifying what might be called the macro-physics, include the neglect of effects of rotation and magnetic fields (implicit in the assumption of spherical symmetry), as well as the assumption that material mixing occurs only in convectively unstable regions, or possibly as a result of molecular diffusion and settling; also, convective energy transport is treated crudely through some form of mixing-length approximation and the contribution to hydrostatic balance from the turbulent motion in the convection zone, usually called turbulent pressure, is ignored.

scholarly journals 29. The internal constitution of sunspots

1958 ◽  
Vol 6 ◽  
pp. 263-274 ◽  
Author(s):  
A. Schlüter ◽  
S. Temesváry
Keyword(s):  
Magnetic Field ◽  
Physical Properties ◽  
Flux Tube ◽  
Energy Transport ◽  
Convection Zone ◽  
Vertical Component ◽  
Relative Distribution ◽  
Physical Processes ◽  
Internal Constitution ◽  
The Magnetic Field

The constitution of stationary single sunspots of circular shape is considered. Account is taken of the mechanical effects of the magnetic field, including those which arise from the curvature of the lines of force. To make the system of magneto-hydrostatic equations manageable, it is assumed that the relative distribution of the vertical component of the magnetic field is the same across the flux-tube of the spot in all depths. Preliminary results indicate that suppression of convective energy transport by the magnetic field in those depths in which ionization of hydrogen takes place, will give the essential observable properties of sunspots, relatively independent on the asumptions about the physical processes in greater depths. There the physical properties of matter can deviate but very little from those of the indisturbed hydrogen convection zone.

scholarly journals Atmospheric parameters and accelerations in the outer parts of luminous hot stars

1989 ◽  
Vol 113 ◽  
pp. 287-288
Author(s):  
Hans Nieuwenhuijzen ◽  
Cornells de Jager
Keyword(s):  
Radiation Pressure ◽  
Dynamic Pressure ◽  
Great Part ◽  
Hydrostatic Equilibrium ◽  
Stellar Winds ◽  
Gravitational Acceleration ◽  
Atmospheric Parameters ◽  
Hot Stars ◽  
Plane Parallel ◽  
Turbulent Pressure

In the atmospheres of the most extreme luminous stars, close to the Humphreys-Davidson limit, the inward gravitational acceleration is for a great part compensated by outward accelerations due to radiation pressure, turbulent pressure and dynamic pressure of the stellar winds. As a result the effective acceleration is very small, resulting in blown-up atmospheres that can no longer be considered plane-parallel or in hydrostatic equilibrium.

scholarly journals Turbulence and magnetic spots at the surface of hot massive stars

2010 ◽  
Vol 6 (S273) ◽  
pp. 200-203
Author(s):  
Matteo Cantiello ◽  
Jonathan Braithwaite ◽  
Axel Brandenburg ◽  
Fabio Del Sordo ◽  
Petri Käpylä ◽  
...  
Keyword(s):  
Surface Properties ◽  
Line Profile ◽  
Convection Zone ◽  
Massive Stars ◽  
Convective Zone ◽  
Early Type ◽  
Line Broadening ◽  
Mhd Simulations ◽  
Early Type Stars ◽  
Thermal Line

AbstractHot luminous stars show a variety of phenomena in their photospheres and in their winds which still lack clear physical explanations at this time. Among these phenomena are non-thermal line broadening, line profile variability (LPVs), discrete absorption components (DACs), wind clumping and stochastically excited pulsations. Cantiello et al. (2009) argued that a convection zone close to the surface of hot, massive stars, could be responsible for some of these phenomena. This convective zone is caused by a peak in the opacity due to iron recombination and for this reason is referred to as the “iron convection zone” (FeCZ). 3D MHD simulations are used to explore the possible effects of such subsurface convection on the surface properties of hot, massive stars. We argue that turbulence and localized magnetic spots at the surface are the likely consequence of subsurface convection in early type stars.

scholarly journals On the Equatorial Acceleration of the Sun

1970 ◽  
Vol 4 ◽  
pp. 318-320 ◽  
Author(s):  
Ian W. Roxburgh
Keyword(s):  
Angular Momentum ◽  
Steady State ◽  
Energy Transport ◽  
Meridional Circulation ◽  
Turbulent Energy ◽  
Convective Zone ◽  
Turbulent Convection ◽  
The Sun ◽  
Viscous Transport ◽  
Gradient Models

AbstractThe interaction of rotation and turbulent convection gives rise to a latitude dependent turbulent energy transport. Energy conservation demands a slow meridional circulation in the solar outer convective zone. The transport of angular momentum by this circulation is balanced in a steady state by the turbulent viscous transport across an angular velocity gradient. Models are constructed which give equatorial acceleration as observed on the sun.

scholarly journals New Results in Evolution in the Upper HRD

1991 ◽  
Vol 143 ◽  
pp. 552-552
Author(s):  
E.I. Staritsin
Keyword(s):  
Mass Loss ◽  
Hydrogen Content ◽  
Stellar Wind ◽  
Convection Zone ◽  
Life Time ◽  
Convective Zone ◽  
Theoretical Interpretation ◽  
Helium Burning ◽  
The Core ◽  
Full Life

A theoretical interpretation of the observed upper luminosity limit is suggested here. Staritsin (1989) considered the core hydrogen and helium burning stages in a 64 M⊙ star. Mixing in a semi-convection zone in a diffusion approximation (Staritsin, 1987) and mass loss by stellar wind (de Jager et al., 1988) were taken into account. During MS evolution the star looses half of its initial envelope. After MS evolution an intermediate convective zone appears. The hydrogen content in the shell source increases. As a result, the star burns helium in its blue supergiant stage. After the hydrogen content in the envelope has decreased to 10% of its mass, the star looses mass with Wolf-Rayet mass loss rates according to de Jager et al. (1988). The star has a WR character during 5% of its full life time.

Venus: Energy Transport and Winds

2013 ◽  
Author(s):  
Andrew P. Ingersoll
Keyword(s):  
Energy Transport ◽  
Equilibrium Temperature ◽  
Blackbody Radiation ◽  
Hydrostatic Equilibrium ◽  
Momentum Transport ◽  
Lapse Rate ◽  
Temperature Structure ◽  
Hadley Cells ◽  
Equilibrium Emission

This chapter examines the modern-day climate of Venus, focusing on the role of winds in energy transfer. It first explains how radiation and convection influence the temperature structure of Venus's atmosphere before discussing other basic physical processes such as Hadley cells and the accompanying winds. It also considers gases in hydrostatic equilibrium, adiabatic lapse rate and stability, the flux and intensity of electromagnetic radiation, blackbody radiation and the Planck function, blackbodies in the solar system, radiative transfer, optically thick atmosphere, radiative-convective equilibrium, emission of radiation to space, equilibrium temperature, energy transport by fluid motions and eddies, eddy momentum transport, and the phenomenon of superrotation.

scholarly journals Magnetic confinement of the solar tachocline: influence of turbulent convective motions

2010 ◽  
Vol 6 (S271) ◽  
pp. 399-400
Author(s):  
Antoine Strugarek ◽  
Allan Sacha Brun ◽  
Jean-Paul Zahn
Keyword(s):  
Convection Zone ◽  
Magnetic Coupling ◽  
Magnetic Confinement ◽  
Convective Zone ◽  
Solar Interior ◽  
The Sun ◽  
Poloidal Field ◽  
Convective Motions ◽  
Radiation Zone ◽  
Field Lines

AbstractWe present the results of 3D simulations, performed with the ASH code, of the nonlinear, magnetic coupling between the convective and radiative zones in the Sun, through the tachocline. Contrary to the predictions of Gough & McIntyre (1998), a fossil magnetic field, deeply buried initially in the solar interior, will penetrate into the convection zone. According to Ferraro's law of iso-rotation, the differential rotation of the convective zone will thus expand into the radiation zone, along the field lines of the poloidal field.

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