scholarly journals Atmospheric Diagnostics of Wolf-Rayet Stars

1988 ◽  
Vol 108 ◽  
pp. 148-149
Author(s):  
C. Doom
Keyword(s):  
Mass Loss ◽  
Optical Depth ◽  
Stellar Wind ◽  
Free Parameter ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Accurate Data ◽  
Slowly Varying Function

Wolf-Rayet (WR) stars are the descendants of massive stars that have lost their hydrogen rich envelope. Recently more accurate data on WR stars have become available: mass-loss rates (van der Hucht et al. 1986), radii and luminosities (Underhill 1983, Nussbaumer et al. 1982).It may therefore be worthwhile to investigate if combinations of observed parameters shed some light on the structure of the extended stellar wind of WR stars.In many WR stars the photosphere is situated in the stellar wind. We assume that the wind is stationary and isotropic. Further we assume a velocity law v(r)=v∞(1−Rs/r)β where v∞ is the terminal velocity of the wind in km/s, Rs is the radius where the wind acceleration starts and β > 0 is a free parameter. We can then easily compute the level R in the wind where the photosphere is located (de Loore et al. 1982): R is the solution of the equation 6.27 10−9 τat R v∞/ = fβ(Rs/R) where τat is the optical depth at the photosphere (2/3 or 1), (>0) is the mass loss rate in M⊙/yr and fβ > 1 is a slowly varying function (Doom 1987).

scholarly journals New Solutions to Line-Driven Winds of Hot Massive Stars

2016 ◽  
Vol 12 (S329) ◽  
pp. 401-401
Author(s):  
Alex C. Gormaz-Matamala ◽  
Michel Curé ◽  
Lydia Cidale ◽  
Roberto Venero
Keyword(s):  
Mass Loss ◽  
Optical Depth ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Hydrodynamic Models ◽  
Self Consistent ◽  
Wind Theory ◽  
Line Force

AbstractIn the frame of radiation driven wind theory (Castor et al.1975), we present self-consistent hydrodynamical solutions to the line-force parameters (k, α, δ) under LTE conditions. Hydrodynamic models are provided by HydWind (Curé 2004). We evaluate these results with those ones previously found in literature, focusing in different regions of the optical depth to be used to perform the calculations. The values for mass-loss rate and terminal velocity obtained from our calculations are also presented.We also examine the line-force parameters for the case when large changes in ionization throughout the wind occurs (δ-slow solutions, Curé et al.2011).

scholarly journals On the significance of mass loss for the evolution of massive stars

1981 ◽  
Vol 59 ◽  
pp. 265-270
Author(s):  
L.R. Yungelson ◽  
A.G. Massevitch ◽  
A.V. Tutukov
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Hydrogen Burning ◽  
B Stars ◽  
The Core ◽  
Input Parameters ◽  
Satisfactory Theory

It is shown that mass loss by stellar wind with rates observed in O, B-stars cannot change qualitatively their evolution in the core hydrogen-burning stage. The effects, that are usually attributed to the mass loss, can be explained by other causes: e.g., duplicity or enlarged chemically homogeneous stellar cores.The significance of mass loss by stellar wind for the evolution of massive stars was studied extensively by numerous authors (see e.g. Chiosi et al. (1979) and references therein). However, the problem is unclear as yet. There does not exist any satisfactory theory of mass loss by stars. Therefore one is usually forced to assume that mass loss rate depends on some input parameters.

scholarly journals Wind inhibition by X-ray irradiation in HMXBs: the influence of clumping and the final X-ray luminosity

2018 ◽  
Vol 620 ◽  
pp. A150 ◽  
Author(s):  
J. Krtička ◽  
J. Kubát ◽  
I. Krtičková
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
High Mass ◽  
Small Scale ◽  
X Rays ◽  
X Ray ◽  
X Ray Binaries

Context. In wind-powered X-ray binaries, the radiatively driven stellar wind from the primary may be inhibited by the X-ray irradiation. This creates the feedback that limits the X-ray luminosity of the compact secondary. Wind inhibition might be weakened by the effect of small-scale wind inhomogeneities (clumping) possibly affecting the limiting X-ray luminosity. Aims. We study the influence of X-ray irradiation on the stellar wind for different radial distributions of clumping. Methods. We calculate hot star wind models with external irradiation and clumping using our global wind code. The models are calculated for different parameters of the binary. We determine the parameters for which the X-ray wind ionization is so strong that it leads to a decrease of the radiative force. This causes a decrease of the wind velocity and even of the mass-loss rate in the case of extreme X-ray irradiation. Results. Clumping weakens the effect of X-ray irradiation because it favours recombination and leads to an increase of the wind mass-loss rate. The best match between the models and observed properties of high-mass X-ray binaries (HMXBs) is derived with radially variable clumping. We describe the influence of X-ray irradiation on the terminal velocity and on the mass-loss rate in a parametric way. The X-ray luminosities predicted within the Bondi-Hoyle-Lyttleton theory agree nicely with observations when accounting for X-ray irradiation. Conclusions. The ionizing feedback regulates the accretion onto the compact companion resulting in a relatively stable X-ray source. The wind-powered accretion model can account for large luminosities in HMXBs only when introducing the ionizing feedback. There are two possible states following from the dependence of X-ray luminosity on the wind terminal velocity and mass-loss rate. One state has low X-ray luminosity and a nearly undisturbed wind, and the second state has high X-ray luminosity and exhibits a strong influence of X-rays on the flow.

scholarly journals Infrared observations of HDE 226868/Cyg X-1 and HDE 245770/A0535+26

1979 ◽  
Vol 83 ◽  
pp. 139-142
Author(s):  
P. Persi ◽  
M. Ferrari Toniolo ◽  
G. Spada
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Circumstellar Envelope ◽  
Infrared Observations ◽  
The Difference ◽  
Radiation Processes ◽  
Ultraviolet Observations

We know from Copernicus ultraviolet observations that all O-type stars are losing mass by stellar wind. The ionized expanding circumstellar envelope formed by the stellar wind is emitting through free-free and bound-free radiation processes. This radiation is detectable at the infrared wavelengths where the stellar continuum is negligible. The measurement of the IR excess (defined as the difference between the total flux and the stellar continuum at a given wavelength) and the knowledge of the terminal velocity of the envelope, allow us to derive for OB stars the mass loss rate. From the analysis of our IR observations of two O stars, HDE 226868 and HDE 245770, identified as optical counterpart of X-ray sources, we give an estimate of their mass loss rate. The IR observations were carried out with the Jungfraujoch 76 cm telescope using a GE bolometer with a focal plane chopping system and with the Merate 132 cm telescope using an InSb detector.

scholarly journals Ionisation fractions and mass-loss in O stars

1987 ◽  
Vol 122 ◽  
pp. 449-450
Author(s):  
Raman K. Prinja ◽  
Ian D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Column Density ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Stellar Radius ◽  
Left Part ◽  
Hr Diagram

The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞, where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞) for N V and C IV.

scholarly journals Infrared Observations of Mass Loss from Massive Stars

1991 ◽  
Vol 143 ◽  
pp. 281-288
Author(s):  
M.J. Barlow
Keyword(s):  
Ir Spectroscopy ◽  
Mass Loss ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Recombination Line ◽  
Infrared Observations ◽  
Use Of Space ◽  
Ionization Structure ◽  
Line Analysis

The future use of space-borne IR spectroscopy to determine the ionization structure and abundances in the outer winds of WR stars is described. A mass loss rate of 1.7×10-5 M⊙ yr–1 has been derived from 10 μm photometry of the WO2 star Sanduleak 5 (WR 142). The He/H number ratios in the winds of P Cyg and AG Car have been derived from a recombination line analysis of their 1-4 μm spectra and mass loss rates of 2.2×10-5 M⊙ yr–1 and 3.7×10-5 M⊙ yr–1 have been respectively derived for them.

scholarly journals Mass loss and evolution of massive stars in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 480-482 ◽  
Author(s):  
Claus Leitherer ◽  
Norbert Langer
Keyword(s):  
Mass Loss ◽  
Iterative Procedure ◽  
Metal Content ◽  
Loss Rate ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Magellanic Clouds ◽  
Evolutionary Models ◽  
Low Metallicity ◽  
Self Consistency

The structure and evolution of massive stars is significantly influenced by effects of chemical composition in a low-metallicity environment (as compared to the solar neighbourhood, SN), such as the Magellanic Clouds. A fundamental ingredient in evolutionary models is the stellar mass-loss rate M. Lower metal content decreases the mass-loss rates derived theoretically, which in turn affects the stellar evolution models. On the other hand, different evolutionary models predict different stellar parameters (especially L), which again influence M so that an iterative procedure is required to achieve self-consistency.

scholarly journals Stellar wind models of central stars of planetary nebulae

2020 ◽  
Vol 635 ◽  
pp. A173 ◽  
Author(s):  
J. Krtička ◽  
J. Kubát ◽  
I. Krtičková
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Terminal Velocity ◽  
Asymptotic Giant Branch ◽  
Central Stars ◽  
Loss Rates

Context. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M⊙. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for Teff ≈ 10 kK) and fade away at the white dwarf cooling track (below Teff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung–Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about Teff = 40−50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s−1 to a few thousands of km s−1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

Relativistic accretion disk winds under relativistic radiation transfer

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Nao Takeda ◽  
Jun Fukue
Keyword(s):  
Velocity Field ◽  
Mass Loss ◽  
Accretion Disk ◽  
Transfer Equation ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Radial Distance ◽  
Terminal Velocity ◽  
Wind Flow ◽  
Disk Radius

Abstract Relativistic accretion disk winds driven by disk radiation are numerically examined by calculating the relativistic radiative transfer equation under a plane-parallel approximation. We first solve the relativistic transfer equation iteratively, using a given velocity field, and obtain specific intensities as well as moment quantities. Using the obtained flux, we then solve the vertical hydrodynamical equation under the central gravity, and obtain a new velocity field and the mass-loss rate as an eigenvalue. We repeat these double iteration processes until both the intensity and velocity profiles converge. We further calculate these vertical disk winds at various disk radii for appropriate boundary conditions, and obtain the mass-loss rate as a function of a disk radius for a given disk luminosity. Since in the present study we assume a vertical flow, and the rotational effect is ignored, the disk wind can marginally escape for the Eddington disk luminosity. When the disk luminosity is close to the Eddington one, the wind flow is firstly decelerated at around z ∼ r, and then accelerated to escape. For a larger disk luminosity, on the other hand, the wind flow is monotonically accelerated to infinity. Under the boundary condition that the wind terminal velocity is equal to the Keplerian speed at the disk, we find that the normalized mass-loss rate per unit area, $\skew9\hat{\skew9\dot{J}}$, is roughly expressed as $\skew9\hat{\skew9\dot{J}} \sim 3 (r_{\rm in}/r_{\rm S}) \Gamma _{\rm d} \tau _{\rm b} (r/r_{\rm S})^{-5/2}(1-\sqrt{r_{\rm in}/r})$, where rin is the disk inner radius, rS is the Schwarzschild radius of the central object, Γd is the disk normalized luminosity, τb is the wind optical depth, and r is the radial distance from the center.

scholarly journals The Circumstellar Structure Around Supernovae

1988 ◽  
Vol 101 ◽  
pp. 15-18
Author(s):  
P. Lundqvist ◽  
C. Fransson
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Time Dependent ◽  
Temperature Structure ◽  
Radio Observations ◽  
Turn On ◽  
Sn 1987A ◽  
Circumstellar Medium

AbstractThe time dependent ionization and temperature structure of the circumstellar medium around supernovae has been calculated, in order to interpret recent supernova radio observations. For a stellar wind origin of the circumstellar medium, we relate the time of radio turn-on to the progenitor mass loss rate. We also show that large column densities for the UV resonance lines are expected. The results are applied to SN 1979c, SN 1980k and SN 1987A.

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