scholarly journals Radiatively-Driven Stellar Winds

1986 ◽  
Vol 89 ◽  
pp. 75-87 ◽  
Author(s):  
L.B. Lucy
Keyword(s):  
Radiation Pressure ◽  
Stellar Winds ◽  
Radiation Hydrodynamics ◽  
Marked Contrast ◽  
Hot Stars ◽  
Supersonic Zones

In this review, attention will be focussed exclusively on the winds of hot stars, concentrating for the most part on spectral types 0 and B. For these stars, a clear consensus has emerged that it is the gradient of selective radiation pressure - i.e., line-driving - that explains the high terminal velocities, typically ~ 2000 km s−1, of their winds. Accordingly, few would now doubt that the supersonic zones of these winds present us with rather clean examples of line-driven flow, whose investigation therefore properly belongs under the heading “Radiation Hydrodynamics”. Moreover, in marked contrast with other astronomical environments where line-driven winds may exist, the stellar case is geometrically and parametrically well defined and is thus by far the best natural example from which to learn about such flows.

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 Non-LTE line blanketed atmospheres for hot stars

1997 ◽  
Vol 189 ◽  
pp. 209-216
Author(s):  
D. J. Hillier
Keyword(s):  
Atomic Data ◽  
Computational Techniques ◽  
Stellar Winds ◽  
Hot Stars ◽  
Computing Power ◽  
Plane Parallel ◽  
Spectroscopic Analyses ◽  
Recent Advances ◽  
Parallel Approximation

The modeling of hot star atmospheres falls into two broad classes: those where the plane parallel approximation can be used, and those where the effects of spherical extension and stellar winds are important. In both cases non-LTE modeling is a necessity for reliable spectroscopic analyses.While simple ions (e.g., H, He I, and He II) have been treated routinely in non-LTE for many years it is only recently that advances in computing power, computational techniques, and the availability of atomic data have made it feasible to perform non-LTE line blanketing calculations. Present models, with varying degrees of approximation and sophistication, are now capable of treating the effects of tens of thousands of lines. We review the latest efforts in incorporating non-LTE line blanketing, highlighting recent advances in the modeling of 0 stars, hot sub-dwarfs, Wolf-Rayet stars, novae, and supernovae.

Radiation Pressure and Accelerating Stellar Winds

1971 ◽  
Vol 169 ◽  
pp. 441 ◽  
Author(s):  
J. M. Marlborough
Keyword(s):  
Radiation Pressure ◽  
Stellar Winds

Stellar mass loss and atmospheric Instability

1988 ◽  
Vol 108 ◽  
pp. 102-113
Author(s):  
Cornelis de Jager ◽  
Hans Nieuwenhuijzen
Keyword(s):  
Mass Loss ◽  
Radiation Pressure ◽  
Stellar Mass ◽  
Stellar Winds ◽  
Evolved Stars ◽  
Upper Limit ◽  
Atmospheric Instability ◽  
Turbulent Pressure ◽  
Loss Component ◽  
Break Up

AbstractA review is given of rate of mass-loss values in the upper part of the Hertzsprung-Russell diagram. Near the luminosity limit of stellar existance = −10−4 M⊙ yr−1. Episodical mass loss in bright variable super- and hypergiants does not significantly increase this value. For Wolf-Rayet stars the rate of mass loss is larger by a factor 140 than for non-evolved stars with the same Teff and L; for C stars this factor is ten. This can be explained qualitatively. Rotation appears hardly to influence the rate of mass loss except for vrot-values close to the break-up velocity. This is in accordance with theory. We suggest the existence of a Red Supergiant Branch; along that branch mass loss is virtually independent of luminosity. Stellar winds along the upper limit of stellar existence are mainly due: to radiation pressure for hot supergiants (≳ 10 000 K); to turbulent pressure for cool supergiants (3000-10 000 K), and to dust-driven and pulsation-driven winds for cooler stars. The turbulent pressure may originate in largescale stochastic motions as observed in Alpha Cyg. Episodical mass loss, as observed in P Cyg, HR 8752 and other Very Luminous Variables may be due to occasional violent stochastic motions, resulting in a shock-driven episodical mass-loss component.

scholarly journals Dust Driven Winds from Pulsating Stars

1993 ◽  
Vol 137 ◽  
pp. 572-574 ◽  
Author(s):  
E.A. Dorfi ◽  
M.U. Feuchtinger ◽  
S. Höfner
Keyword(s):  
The Self ◽  
Time Dependent ◽  
Full Description ◽  
Stellar Winds ◽  
Dust Formation ◽  
Radiation Hydrodynamics ◽  
Simple Description ◽  
Pulsating Stars ◽  
Self Consistent ◽  
Different Parts

The cool extended atmospheres of late type giants are sites where dust formation takes place. Radiation pressure on the dust grains is an important force for driving the slow but massive winds observed in such objects. Existing calculations of dust driven stellar winds (e.g. Bowen 1988, Fleischer et al. 1991) suffer from the fact that they include approximations at various levels for different parts of the problem like the hydrodynamics or the dust formation. Furthermore they do not include time-dependent radiative transfer.In order to overcome these insufficiencies we plan to calculate self-consistent models of dust driven winds with a full description of both the radiation hydrodynamics and the time-dependent dust formation. As a first step, however, we concentrate our investigations on the self-consistent description of the radiation hydrodynamics adopting only a simple description of the dust opacities.

scholarly journals A Hot Corona Model for O-Stars and WR Stars

1982 ◽  
Vol 99 ◽  
pp. 209-213
Author(s):  
W. Robbrecht ◽  
C. de Loore ◽  
G. Olson
Keyword(s):  
Radiation Pressure ◽  
Slow Component ◽  
Energy Sources ◽  
X Rays ◽  
Stored Energy ◽  
Atmospheric Models ◽  
Hot Stars ◽  
Two Component ◽  
Hot Corona ◽  
Radiation Cooling

Atmospheric models are presented for the outer layers of hot stars, O, of and Wolf-Rayet stars. The model is a two component hybrid model, consisting of a rapidly expanding component and a slower component. for the rapidly expanding component the energy sources are radiation pressure, a deposit of internally generated and stored energy, and radiation cooling. In this way a coronal layer with temperatures of the order of 4–7 million K is generated, with an extent of 1 to 2 stellar radii. The mass loss rates range between 10−6 and 10−4 Mo yr−1. The stellar wind velocity at infinity is of the order of 4000 km s−1. It is assumed that this rapid component interacts with the slow component, and gives rise to shocks. The corona as well as the shocks generated by the interaction of the two components can explain the observed X-rays.

scholarly journals Theory and observations of non-thermal phenomena in hot massive binaries

1995 ◽  
Vol 163 ◽  
pp. 438-449
Author(s):  
Richard L. White ◽  
Wan Chen
Keyword(s):  
Thermal Radiation ◽  
Binary Systems ◽  
Theoretical Work ◽  
Stellar Winds ◽  
Hot Stars ◽  
Thermal Emissions ◽  
Γ Rays ◽  
Physical Effects ◽  
Thermal Phenomena ◽  
Colliding Winds

The shock between the colliding winds in binary systems containing two massive stars accelerates particles to relativistic energies. These energetic particles can produce observable non-thermal radiation from the radio to γ-rays. The important physical processes in such systems are very similar to those we have proposed for non-thermal emissions from single hot stars, which have shocks generated by instabilities in the radiatively driven stellar winds. This paper discusses the theory and observations of non-thermal radiation in the radio, X-ray, and γ-ray regions from both single stars and massive binaries. Similarities and differences between the two types of systems are outlined. We discuss two important physical effects that apparently have been neglected in previous theoretical work on colliding wind binaries.

Sign in / Sign up

Export Citation Format

Share Document