scholarly journals Angular Velocity Distribution in Rotating Massive Stars

1967 ◽  
Vol 20 (6) ◽  
pp. 651
Author(s):  
MPC Legg
Keyword(s):  
Angular Velocity ◽  
Velocity Distribution ◽  
Radiation Pressure ◽  
Electron Scattering ◽  
Differential Rotation ◽  
Meridional Circulation ◽  
Massive Stars ◽  
Effects Of Radiation ◽  
Uniform Composition

The angular velocity distribution in rotating massive stars with uniform composition and opacity due to electron scattering is calculated on the assumption that meridional circulation is neglible. The effects of radiation pressure are taken into account in the determination of the differential rotation and the angularvelocity is assumed to be ndependent of latitude.

scholarly journals The 2D dynamics of the differentially rotating envelope of massive stars

2016 ◽  
Vol 12 (S329) ◽  
pp. 409-409
Author(s):  
Delphine Hypolite ◽  
Stéphane Mathis ◽  
Michel Rieutord
Keyword(s):  
Differential Rotation ◽  
Main Sequence ◽  
Meridional Circulation ◽  
Massive Stars ◽  
Boussinesq Approximation ◽  
Core Size ◽  
Dynamical Boundary Condition ◽  
The Core ◽  
Baroclinic Flow ◽  
2D Model

We build a 2D model of the radiative envelope of main sequence massive stars. We set a dynamical boundary condition at the bottom of the radiative envelope at η = rC/R (where rC is the core size and R the radius of the star) to account for the differential rotation of the convective core as computed in 3D simulations (e.g. Browning et al. (2004, IAUS, 224, 149). We seek the differential rotation and associated meridional circulation induced by such a shear competing with the baroclinic flow of the stably stratified radiative envelope using the Boussinesq approximation.

scholarly journals αΛ-dynamos

1991 ◽  
Vol 130 ◽  
pp. 147-150 ◽  
Author(s):  
A. Brandenburg ◽  
D. Moss ◽  
M. Rieutord ◽  
G. Rüdiger ◽  
I. Tuominen
Keyword(s):  
Angular Velocity ◽  
Stress Tensor ◽  
Reynolds Stress ◽  
Differential Rotation ◽  
Eddy Viscosity ◽  
Meridional Circulation ◽  
Momentum Equation ◽  
Constant Angular Velocity ◽  
Reynolds Stress Tensor ◽  
Magnetic Diffusivity

Abstract In contrast to αω-dynamos, where the angular velocity is arbitrarily prescribed, we consider here αΛ-dynamos, for which the differential rotation and meridional circulation are solutions of the momentum equation. The non-diffusive parts of the Reynolds stress tensor are parameterized by the Λ-effect. In earlier investigations we have shown that the turbulent magnetic diffusivity has to be much smaller than the eddy viscosity, otherwise the dynamo is not oscillatory or else the contours of constant angular velocity are cylindrical, contrary to observations. In the present paper we investigate the effects of compressibility.

scholarly journals The Differential Rotation and Evolution of Spots on UX Arietis from a Sequence of Doppler Images

1991 ◽  
Vol 130 ◽  
pp. 297-308
Author(s):  
Steven S. Vogt ◽  
Artie P. Hatzes
Keyword(s):  
Angular Velocity ◽  
Velocity Distribution ◽  
Differential Rotation ◽  
The Sun ◽  
High Latitudes ◽  
Time Intervals ◽  
A Value ◽  
Angular Velocities ◽  
The Difference

AbstractWe present a sequence of three Doppler images of the spotted RS CVn star UX Arietis obtained over a 5-month interval from August 1986 through January 1987. The spot distribution was quite complex and consisted of a large stable polar spot, a spot near the equator, and several other spots at intermediate positive and negative latitudes. The time intervals between successive images were small enough that we were able to reliably track the evolution of the spot distribution, measuring accurate longitudes, latitudes, and areas of the major spots, as well as their drift rates in longitude and latitude. The longitudinal drifts of spot features at equatorial, intermediate, and high latitudes yielded an accurate measurement of differential rotation. We find that the spotted primary of UX Arietis is indeed rotating differentially and in the sense opposite to that of the Sun, i.e. the poles rotate faster than the equator. The equator is synchronized to the orbital angular velocity, and the angular velocity increases towards either pole. The angular velocity distribution can be expressed as Ω(°/day) = −55.91 + 1.09(±0.09) sin2∅, where ∅ is the latitude. The amount of differential rotation, parameterized as the ratio of the difference between the equatorial and polar angular velocities to the equatorial angular velocity, is then α = −0.020(±0.002), as compared to a value of α = +0.2 for the Sun.

scholarly journals Two-Dimensional Stochastic Motions and the Problem of Differential Rotation for Unrestricted Rotational Rates

1976 ◽  
Vol 71 ◽  
pp. 301-302
Author(s):  
G. Rüdiger
Keyword(s):  
Angular Velocity ◽  
Differential Rotation ◽  
Eddy Viscosity ◽  
Meridional Circulation ◽  
Three Dimensional ◽  
Giant Cells ◽  
List Type ◽  
Two Dimensional ◽  
Latitudinal Dependence ◽  
Anisotropic Viscosity

For dealing analytically with the problem of differential rotation we investigate the spatial dependence of the angular velocity in a rotating turbulent fluid. The original turbulence unaffected by the rotation is assumed to be two-dimensional, where the stochastic motions completely lie in the horizontal planes. From the expression describing the relation between the correlations of rotating and nonrotating turbulent fields the meridional flux of momentum is derived. The resulting rotational law is determined by using Bochner's theorem for homogeneous turbulence as well as the characteristic scales of the turbulence field considered. The conclusions are: (a)The angular velocity ω is increasing toward the outer layers.(b)For 2 Ω ≪ ωc (ωc frequency of turbulent mode) the Biermann-Kippenhahntheory of anisotropic viscosity is deduced. An equatorial acceleration is only caused by a meridional circulation.(c)For 2 Ω ≲ ωc a latitudinal dependence of ω is possible without any meridional circulation. If the two-dimensional eddy viscosity is negative the equatorial regions are accelerated. The expression for the two-dimensional eddy viscosity which has been derived earlier allows negativity in contrast to that for three-dimensional eddy viscosity. The scale length and the scale time of supergranulation as well as of giant cells lead to negative two-dimensional eddy viscosity.

Differential Rotation in Degenerate Stars

1974 ◽  
Vol 53 ◽  
pp. 251-264
Author(s):  
H. M. Van Horn
Keyword(s):  
Angular Momentum ◽  
Angular Velocity ◽  
Velocity Distribution ◽  
Differential Rotation ◽  
Final Phase ◽  
Cooling Phase

The problem of the development of the angular velocity distribution during the final phase of gravitational contraction of a star immediately prior to the onset of degeneracy and during the subsequent cooling phase is surveyed. Processes that may affect this distribution are discussed at some length, and estimates of the timescales for redistribution of the angular momentum are given for each process. Possible effects on the evolution and observable consequences are briefly considered.

Inelastic Electron Scattering from Valence Electrons in Aluminum

1976 ◽  
Vol 34 ◽  
pp. 462-463
Author(s):  
P. E. Batson ◽  
C. H. Chen ◽  
J. Silcox
Keyword(s):  
Electron Scattering ◽  
Single Scattering ◽  
Three Dimensions ◽  
Inelastic Electron ◽  
Weak Beam ◽  
Scattering Spectrum ◽  
Valence Electrons ◽  
Diffraction Patterns ◽  
Electronic Scattering

We wish to report in this paper measurements of the inelastic scattering component due to the collective excitations (plasmons) and single particlehole excitations of the valence electrons in Al. Such scattering contributes to the diffuse electronic scattering seen in electron diffraction patterns and has recently been considered of significance in weak-beam images (see Gai and Howie) . A major problem in the determination of such scattering is the proper correction for multiple scattering. We outline here a procedure which we believe suitably deals with such problems and report the observed single scattering spectrum.In principle, one can use the procedure of Misell and Jones—suitably generalized to three dimensions (qx, qy and #x2206;E)--to derive single scattering profiles. However, such a computation becomes prohibitively large if applied in a brute force fashion since the quasi-elastic scattering (and associated multiple electronic scattering) extends to much larger angles than the multiple electronic scattering on its own.

scholarly journals Radiation-Driven Stellar Eruptions

Galaxies ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 10 ◽  
Author(s):  
Kris Davidson
Keyword(s):  
Mass Loss ◽  
Radiation Pressure ◽  
Central Region ◽  
Massive Stars ◽  
Variable Stars ◽  
Blast Waves ◽  
Subsequent Evolution ◽  
Fundamental Causes ◽  
Radiative Output ◽  
Luminous Blue Variable

Very massive stars occasionally expel material in colossal eruptions, driven by continuum radiation pressure rather than blast waves. Some of them rival supernovae in total radiative output, and the mass loss is crucial for subsequent evolution. Some are supernova impostors, including SN precursor outbursts, while others are true SN events shrouded by material that was ejected earlier. Luminous Blue Variable stars (LBV’s) are traditionally cited in relation with giant eruptions, though this connection is not well established. After four decades of research, the fundamental causes of giant eruptions and LBV events remain elusive. This review outlines the basic relevant physics, with a brief summary of essential observational facts. Reasons are described for the spectrum and emergent radiation temperature of an opaque outflow. Proposed mechanisms are noted for instabilities in the star’s photosphere, in its iron opacity peak zones, and in its central region. Various remarks and conjectures are mentioned, some of them relatively unfamiliar in the published literature.

Feasibility of Extracting Velocity Distribution in Choriocapillaris in Human Eyes from ICG Dye Angiograms

2005 ◽  
Vol 128 (2) ◽  
pp. 203-209 ◽  
Author(s):  
L. Zhu ◽  
Y. Zheng ◽  
C. H. von Kerczek ◽  
L. D. T. Topoleski ◽  
R. W. Flower
Keyword(s):  
Velocity Distribution ◽  
Fluorescence Intensity ◽  
Conversion Factor ◽  
Blood Velocity ◽  
New Approach ◽  
Pixel Location ◽  
Choroidal Vasculature ◽  
Dye Fluorescence ◽  
Human Eyes

Indocyanine green (ICG) dye angiography has been used by ophthalmologists for routine examination of the choroidal vasculature in human eyes for more than 20years. In this study, a new approach is developed to extract information from ICG dye angiograms about blood velocity distribution in the choriocapillaris and its feeding blood vessels. ICG dye fluorescence intensity rise and decay curves are constructed for each pixel location in each image of the choriocapillaris in an ICG angiogram. It is shown that at each instant of time the magnitude of the local instantaneous dye velocity in the choriocapillaris is proportional to both the slope of the ICG dye fluorescence intensity curve and the dye concentration. This approach leads to determination of the absolute value of blood velocity in the choriocapillaris, assuming an appropriate scaling, or conversion factor can be determined. It also enables comparison of velocities in different regions of the choriocapillaris, since the conversion factor is independent of the vessel location. The computer algorithm developed in this study can be used in clinical applications for diagnostic purposes and for assessment of the efficacy of laser therapy in human eyes.

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