Radiation-driven Winds Research Articles

Models of radiation-driven winds from general relativistic neutron stars

view Abstract Citations (63) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Models of Radiation-driven Winds from General Relativistic Neutron Stars Paczynski, B. ; Proszynski, M. Abstract Fully relativistic models of winds driven by the super-Eddington luminosity of X-ray bursting neutron stars are presented. It is found that all the super-Eddington energy flux is used to gently blow off matter with a terminal velocity of the order of 0.01 c, and that the radiative luminosity never exceeds the Eddington limit by more than 1 percent. The photospheric radius of an outflowing envelope is always at least 10 times larger than the radius of a neutron star, and the effective temperature is correspondingly low, always smaller than 10 exp 6.8 K. There is an almost continuous transition between static extended envelopes of neutron stars that have a slightly sub-Eddington luminosity and outflowing envelopes that are slightly super-Eddington and have a low mass outflow rate. Publication: The Astrophysical Journal Pub Date: March 1986 DOI: 10.1086/164012 Bibcode: 1986ApJ...302..519P Keywords: Neutron Stars; Relativistic Effects; Stellar Radiation; Stellar Structure; Stellar Winds; X Ray Sources; Computational Astrophysics; Flow Velocity; Photosphere; Radiative Transfer; Stellar Luminosity; Stellar Temperature; Astrophysics; RELATIVITY; STARS: INTERIORS; STARS: NEUTRON; STARS: WINDS; X-RAYS: BURSTS full text sources ADS |

CONNECTION BETWEEN NONRADIAL PULSATIONS AND STELLAR WINDS IN MASSIVE STARS. VIII - SUMMARY COMMENTS ON THE STATE OF STELLAR-WIND THEORY AS IT RELATES TO NONRADIAL PULSATIONS

ABSTRACT Certain modifications of the stellar-wind theory reported by Castor et al. (1975) have improved its agreement with observations of O star winds and answered some questions regarding its approximations. The present status of agreement between radiatively-driven wind theory and observations of hot-star winds is discussed. It is pointed out that the state of the comparison between radiatively-driven wind theory and observation for Wolf-Rayet stars has changed recently with two important discoveries. According to one, multiline scattering can provide mass-loss rates well in excess of the 'single scattering limit'. The second discovery is that at least one W-R star is very hot. The temperature referred to the thermalizing radius of V444 Cygni is about 95,000 K. All instabilities considered so far are drift instabilities, at least in the realistic limit that isothermal oscillations are assumed.

The interpretation of flows in molecular clouds

Stellar winds interacting with gas in dense molecular clouds produce flows which may be initially energy or momentum driven. A criterion for this is derived which depends sensitively on the wind velocity. Flows may change from one regime to another depending on the gas distribution about the wind source and these changes are discussed for power law density distributions. In general, the flows observed in CO associated with infrared point sources seem to be in the energy driven regime. By combining CO observations with radio continuum flux measurements, wind parameters are derived for several of these sources. There is some evidence from the derived parameters that high (L*≲2×103L⊙) luminosity sources have radiatively-driven winds. Lower luminosity source winds are driven by some agency as yet unknow. We suggest that the widths of infrared lines from wind sources seriously underestimate the wind terminal velocities.

Some effects of rotation on the structure and dynamics of a radiation-driven wind from a hot star

On considere quelques-unes des facons dont la rotation modifie un vent stellaire induit par rayonnement, tel que l'on decrit Castor, Abbott et Klein. Application des resultats aux etoiles Be

Stellar winds driven by multiline scattering

view Abstract Citations (83) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar winds driven by multiline scattering Friend, D. B. ; Castor, J. I. Abstract A model of a radiation-driven stellar wind with overlapping spectral lines is presented. It is based on the Castor, Abbott, and Klein (CAK) theory (1975). The presence of overlapping lines allows a photon to be scattered many times in different lines. A random separation is assumed between strong lines, which makes it possible to find the angular distribution of the wavelength-averaged intensity of radiation from the star. The properties of the wind at any point depend on this intensity, which in turn depends on the structure of the wind. A self-consistent wind model is found. The mass loss rate does not saturate as line overlap becomes more pronounced, but continues to increase. The terminal velocity is much larger than in the CAK model, while the velocity law is shallower. This wind is much more efficient in ejecting matter from the star than the CAK wind. Publication: The Astrophysical Journal Pub Date: September 1983 DOI: 10.1086/161289 Bibcode: 1983ApJ...272..259F Keywords: Electromagnetic Scattering; Radiative Transfer; Stellar Mass Ejection; Stellar Radiation; Stellar Spectra; Stellar Winds; Angular Distribution; O Stars; Radiation Pressure; Stellar Atmospheres; Stellar Models; Wind Velocity; Astrophysics full text sources ADS |

Infrared photometry and mass loss rates for Of-type stars

view Abstract Citations (27) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared photometry and mass loss rates for OF-type stars. Persi, P. ; Ferrari-Toniolo, M. ; Grasdalen, G. L. Abstract The Of-type stars represent an interesting class of luminous O-type stars characterized by emission in N III lambda 4640. Castor et al. (1975) proposed a model in which the wind from Of stars is driven by the force of radiation absorbed in a large number of spectral lines. In this connection, accurate determinations of mass loss rates are very important in understanding the physical processes in the winds of Of-type stars and in studying their evolution. The present investigation reports additional mass loss rates derived from accurate IR photometry from 2.3 microns up to 10 microns of 15 Of-type stars. The considered IR observations suggest that a unique model cannot explain the wind's properties in Of-type stars. While the radiation-driven wind model may be applied for some Of-type stars, the observed high wind momentum in other stars, especially in Of stars, requires an additional or different mechanism to drive the wind as proposed for WR stars. Publication: The Astrophysical Journal Pub Date: June 1983 DOI: 10.1086/161069 Bibcode: 1983ApJ...269..625P Keywords: Infrared Astronomy; Infrared Photometry; Mass Flow Rate; O Stars; Stellar Mass Ejection; Stellar Spectrophotometry; Astronomical Catalogs; Binary Stars; Stellar Luminosity; Stellar Models; Astrophysics full text sources ADS | data products SIMBAD (17)

Radiation-driven winds in X-ray binaries

view Abstract Citations (119) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiation driven winds in X-ray binaries. Friend, D. B. ; Castor, J. I. Abstract The properties of a radiation-driven stellar wind in an X-ray binary system are discussed. The Castor, Abbott, and Klein line-driven wind model is used, but the effects of the compact companion (gravity and continuum radiation pressure) and the centrifugal force due to orbital motion are included. These forces destroy the spherical symmetry of the wind and can make the mass loss and accretion strong functions of the size of the primary relative to its critical potential lobe. The accretion rate and X-ray luminosity of the known massive X-ray binaries are estimated. It is found that in most systems the wind alone could power the X-ray emission. It also appears that, in the evolution of these systems, there would be a continuous transition from wind accretion to critical potential lobe overflow. The model is also used to make a prediction about the nature of a suspected binary system which is not known to be an X-ray emitter. Publication: The Astrophysical Journal Pub Date: October 1982 DOI: 10.1086/160340 Bibcode: 1982ApJ...261..293F Keywords: Binary Stars; Hot Stars; Stellar Mass; Stellar Models; Stellar Winds; X Ray Binaries; X Ray Sources; B Stars; O Stars; Stellar Luminosity; Stellar Mass Accretion; Stellar Mass Ejection; Astrophysics full text sources ADS | data products SIMBAD (6)

Stellar winds in binary X-ray systems

It is thought that accretion from a strong stellar wind by a compact object may be responsible for the X-ray emission from binary systems containing a massive early-type primary. To investigate the effect of X-ray heating and ionization on the mass transfer process in systems of this type, an idealized model is constructed for the flow of a radiation-driven wind in the presence of an X-ray source of specified luminosity, L sub x. It is noted that for low values of L sub x, X-ray photoionization gives rise to additional ions having spectral lines with wavelengths situated near the peak of the primary continuum flux distribution. As a consequence, the radiation force acting on the gas increases in relation to its value in the absence of X-rays, and the wind is accelerated to higher velocities. As L sub x is increased, the degree of ionization of the wind increases, and the magnitude of the radiation force is diminished in comparison with the case in which L sub x = 0. This reduction leads at first to a decrease in the wind velocity and ultimately (for L sub x sufficiently large) to the termination of radiatively driven mass loss.

Winds in late-type stars: Mechanisms of mass outflow

AbstractFour basic mechanisms have been proposed to explain the acceleration of winds in late-type stars –– thermal pressure gradients, radiation pressure on circumstellar dust grains, momentum addition by Alfvén waves, and momentum addition by periodic shock waves. In this review I describe recent work in applying these mechanisms to stars, and consider whether these mechanisms can work even in principle and whether they are consistent with recent ultraviolet and X-ray data from the IUE and Einstein spacecraft. Thermally-driven winds are likely important for late-type dwarfs, where the mass loss rates are small, and perhaps also in G giants and supergiants, but they cannot operate alone in the K and M giants and supergiants. Radiatively-driven winds are probably unimportant for all cool stars, even the M supergiants with dusty circumstellar envelopes. In principle, Alfvén waves can accelerate winds to high speeds provided the field lines are initially open or forced open by some mechanism, but detailed calculations are needed. Magnetic reconnection is an interesting suggestion for an acceleration mechanism when the field lines are initially closed. For the Mras and semiregular variable supergiants, periodic shock waves provide a simple way of producing rapid mass loss. Thus we are making some progress in understanding mass loss mechanisms for the cool half of the H-R diagram.

The instability of radiation-driven stellar winds

view Abstract Citations (94) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The instability of radiation-driven stellar winds Carlberg, R. G. Abstract The stability of a radiation-driven stellar wind is examined by applying a completely linearized stability analysis to a physically realistic wind model. Three types of instability are found. Both the line-shape and the radiation-driven sound wave instabilities are purely vertical motions which have been previously discovered. A new 'gradient' instability has motion in both the vertical and horizontal directions. Typical growth times of the three instabilities are 150, 1000, and 10,000 seconds, respectively, although the growth time of the line-shape instability is a lower limit. The radiation-driven sound wave and gradient instabilities have density and velocity perturbations suggesting that the wind will tend to break up into clouds or slabs of typical size one-billion to 100-billion cm. The existence of such clumps would alter the dynamics of a wind and the interpretation of observations of winds. Publication: The Astrophysical Journal Pub Date: November 1980 DOI: 10.1086/158428 Bibcode: 1980ApJ...241.1131C Keywords: Astrophysics; Stellar Radiation; Stellar Winds; Flow Stability; Stellar Models; Astrophysics full text sources ADS |

Formation of resonance doublet profiles in rapidly expanding envelopes

Generalization of the escape probability method introduced by Sobolev allows us to study the transfer of spectral line radiation for a resonance doublet in rapidly expanding envelopes. For the cases of outward-accelerating (or equivalently inward-decelerating) and outward-decelerating (or equivalently inward-accelerating) envelopes we derive, in the frame of a three-level atom model, the expressions for the spectral radiation fieldsJ 12 andJ 13, for the resulting radiative force FRE exerted per atom and for the resonance doublet profileE(X)/C c; we take into account the complex radiative coupling, in both resonance transitions 1⇌2 and 1⇌3, between distant parts of the atmosphere. For various physical and geometrical conditions prevailing in the expanding media, we illustrate and discuss the behaviours of those quantities as well as their dependence on the parameters of the model. Namely, we deduce criteria under which resonance doublet profiles formed in outward-accelerating and/or outward-decelerating envelopes would appear to be resolved into double P Cygni profiles. We also stress the importance of treating a resonance doublet as being formed by two distinct resonance transitions when evaluating the resulting radiative force FRE acting on an atom. It is indeed shown that if we use a two-level atom model to represent a resonance doublet-i.e., assigning to it an oscillator strength equal to the sum of the oscillator strengths of both resonance transitions-the amplitude of the resulting radiative force can be underestimated by factors reaching 100% and more in the regions of the expanding envelope which are optically thick to the spectral line radiation. In this context, it would be essential to revise the previous models of radiation-driven winds developed for early-type stars in which the lines belonging to any multiplet were treated as a single line.

Chromospheres, Coronae, and Mass Loss in Stars Hotter than the Sun

AbstractReviews of the mass-loss characteristics of OB stars have been published recently, and the present review therefore emphasizes the A and F stars and very recent results on O and B stars. For the F stars, chromospheric indicators are present in the form of emission lines, seen in visible and ultraviolet wavelengths. Winds are present in A supergiants, but not in main sequence stars, although at least a few of the latter are X-ray sources, indicating the possible existence of coronae. Most OB supergiants are X-ray sources as well, indicating, along with the presence of super-ionization, that these stars have coronae. On the main sequence, the O stars and some B stars (including Be stars in many cases) have mass loss with highly-ionized species in the wind. The winds in the O and B stars are commonly variable. The mass-loss rates do not show a simple dependence on luminosity, contrary to the predictions for radiatively-driven winds.

The structure and appearance of winds from supercritical accretion disks. I - Numerical models

view Abstract Citations (40) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The structure and appearance of winds from supercritical accretion disks. I. Numerical models. Meier, D. L. Abstract Equations for the structure and appearance of supercritical accretion disks and the radiation-driven winds which emanate from them are derived and solved by a steady-state hydrodynamic computer code with a relaxation technique used in stellar structure problems. The present model takes into account the mass of the accreting star, the total accretion rate, a generalization of the disk alpha parameter which accounts for heating by processes in addition to viscosity, and the ratio of the total luminosity to the Eddington luminosity. Solutions indicate that for accretion onto a hard-surfaced star, steady, optically thick winds result for even slightly supercritical accretion, and the object will appear as a supergiant star with a high mass loss rate and a nonblackbody spectrum. Winds from black hole accretion disks are expected to depend on the form of the accretion interior to the critical radius, possibly consisting of no ejection at all, a wind similar to that of a hard-surfaced star, or a column of material ejected from a hole in the accretion disk. Publication: The Astrophysical Journal Pub Date: October 1979 DOI: 10.1086/157428 Bibcode: 1979ApJ...233..664M Keywords: Astrophysics; Stellar Mass Accretion; Stellar Models; Stellar Winds; Supercritical Flow; Binary Stars; Black Holes (Astronomy); Disks (Shapes); Photosphere; Supergiant Stars; Astrophysics; Accretion Disks:Models; Accretion Disks:Stellar Winds; Stellar Winds:Models full text sources ADS |

Radiative amplification of sound waves in the winds of O and B stars

The velocity perturbation associated with an outwardly propagating sound wave in a radiation-driven stellar wind gives rise to a periodic Doppler shifting of absorption lines formed in the flow. A linearized theory applicable to optically thin waves is used to show that the resulting fluctuation in the absorption-line force can cause the wave amplitude to grow. Detailed calculations of the acceleration due to a large number of lines indicate that significant amplification can occur throughout the high-velocity portion of winds in which the dominant force-producing lines have appreciable optical depths. In the particular case of the wind of Zeta Pup (O4f), it is found that the e-folding distance for wave growth is considerably shorter than the scale lengths over which the physical properties of the flow vary. A qualitative estimate of the rate at which mechanical energy due to nonlinear waves can be dissipated suggests that this mechanism may be important in heating the supersonic portion of winds of early-type stars.

An ultraviolet view of stellar winds

Ultraviolet observations of mass-loss effects in O stars have, over the past decade, revealed a broad picture of a phenomenon whose extent was only partially evident from earlier ground-based observations. Ultraviolet resonance lines of a variety of ionization stages of several common elements provide a comprehensive probe of the low-density, extended winds. Three general types of information have been derived from ultraviolet spectroscopy of mass-loss profiles: (1) the nature of the stars which experience mass loss via radiatively-driven winds; (2) the physical conditions in the winds; and (3) variability in the outflow, which in turn may yield clues to the origins of the winds. Observations and results in each of these areas are reviewed, and some new results are included. A good correlation of mass loss rate and luminosity is indicated by the data, in agreement with theoretical predictions. Time variations in the P Cygni profiles may be quite common, with variability on times of hours or longer. Anticipated new observations, which should be possible with existing and planned instrumentation, are described.

Radiatively-driven winds: Model improvements, ionization balance and the infrared spectrum

Recent improvements to theoretical stellar wind models and the results of empirical modelling of the ionization balance and the infrared continuum are discussed. The model of a wind driven by radiation pressure in spectral lines is improved by accounting for overlap of the driving lines, dependence of ionization balance on density, and stellar rotation. These effects produce a softer velocity law than that given by Castor, Abbott and Klein (1975). The ionization balance in ζ Puppis is shown to agree with that estimated for an optically thick wind at a gas temperature of 60,000 K. The ionization model is not unique. The infrared continuum of ζ Pup measured by Barlow and Cohen is fitted to a cool model with a linear rise of velocity with radius; this fit is also not unique. It is concluded we should try to find a model that fits several kinds of evidence simultaneously.

Boundary Condition with Mass Loss: The Radiatively-Driven Wind Model

A brief summary of the current status of radiatively driven wind models for early-type stars is given. A critique of these models is made both on theoretical and observational grounds, and it is concluded that a pure radiatively driven wind is probably not a realistic approximation for 0-star winds. It is argued that probably the wind structure must have an initial high-temperature (“coronal”) region through which the trans-sonic flow takes place, followed by radiative accelerations to very high terminal velocities. Full details of the discussion can be found in Stellar Atmospheres, 2nd Edition, by D. Mihalas, to be published by W. H. Freeman and Company, San Francisco, in Fall 1977.

Characteristics of the blue stars in the dwarf galaxies I ZW 18 and II ZW 40

Among dwarf blue compact galaxies, I Zw 18 and II Zw 40 have continuum and emission-line spectra similar to those of giant H II regions in external galaxies. An analysis of the emission-line spectrum shows that the emissive gas is much hotter than normal galactic H II regions and that the heavy elements Z are highly underabundant unless they are in stages of ionization higher than Z/sup 2 +/. A study of the thermal balance (i) confirms an underabundance of elements heavier than He by a factor of at least 10 compared to their cosmic values, and (ii) shows that most of the interstellar gas is ionized by hot stars, 4.0 x 10/sup 4/ or approx. = =30 M/sub sun/. The He II lambda4686 line observed in emission in I Zw 18 can arise in the optically thin hot envelopes of radiation-driven winds of Of stars. These blue compact galaxies cannot be old galactic systems with a flat mass distribution of newly formed stars. (AIP)

Effects of rapidly diverging flow, heat addition, and momentum addition in the solar wind and stellar winds

The roles of rapid flow tube divergence and heat and momentum addition in one-fluid models of the solar wind and stellar winds and the role of heat addition in two-fluid models of the solar wind ae explored. It is found that under certain circumstances heat addition, momentum addition, or the rapid divergence of a flow tube can produce more than one critical point in the solution topologies of the solar and stellar wind equations. For the solar wind, additional critical points associated with rapid flow tube divergence (e.g., in coronal holes) and/or with momentum addition can lead to high expansion speeds near the coronal base, and these high speeds, in conjuction with a rapid flow tube divergence, may in certain cases produce an increased conductive energy supply to the solar wind. If such an increased conductive energy supply is produced, the need for energy addition above the coronal base is correspondingly reduced. In addition, the high flow speeds at low altitudes make it possible for any required energy addition to occur relatively near the coronal base, so that the need for extended heating of the solar wind may be substantially less than has been suggested in the past. For radiation-drivenmore » stellar winds the additional critical points associated with rapid flow tube divergence can lead to supersonic flow much deeper in the stellar atmosphere than is predicted by radial, spherically symmetric flow models, and this might resolve the apparent conflict between radiation-driven wind models and certain observations of Of stars. In two-fluid solar wind models including proton heat addition it is shown that the radial electron temperature profile has a sufficiently important dynamical influence that the accurate treatment of electron energy transport is a primary prerequisite to obtaining quantitatively significant results. (AIP)« less

Radiation-driven winds in Of stars

view Abstract Citations (1871) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiation-driven winds in Of stars. Castor, J. I. ; Abbott, D. C. ; Klein, R. I. Abstract The large number of subordinate lines of a representative ion are found to have a dominant effect on the force of radiation on material in O star atmospheres. The force is increased over that due to resonance lines alone so that rates of mass loss are obtained which are 100 times greater than previously thought possible. The force is related to the solution of the line-transfer problem, and it becomes a function of the local velocity gradient. A new stellar wind theory, with a different interpretation of the singular point, is developed to treat this situation. The rate of mass loss, and other properties of the model, are uniquely specified by the luminosity, mass, and radius of the star. Alternative static models do not exist. Numerical results give a rate of mass loss equal to .000006 solar mass per year for an O5 star, with a terminal velocity of 1500 km/sec. The rate of mass loss is sensitive to stellar parameters, while the terminal velocity is not. Publication: The Astrophysical Journal Pub Date: January 1975 DOI: 10.1086/153315 Bibcode: 1975ApJ...195..157C Keywords: Astronomical Models; Line Spectra; O Stars; Radiation Pressure; Stellar Mass Ejection; Stellar Winds; Emission Spectra; Main Sequence Stars; Molecular Oscillators; Optical Thickness; Stellar Atmospheres; Stellar Evolution; Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (1)