scholarly journals The influence of inhomogeneities on hot star wind model predictions

2008 ◽  
Vol 4 (S252) ◽  
pp. 283-287 ◽  
Author(s):  
J. Krtička ◽  
L. Muijres ◽  
J. Puls ◽  
J. Kubát ◽  
A. de Koter
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
The Other ◽  
Radiative Force ◽  
Wind Model ◽  
Other Hand ◽  
Model Predictions ◽  
Line Force

AbstractWe study the effect of wind inhomogeneities (clumping) on O star wind model predictions. For this purpose we artificially include clumping into our stationary NLTE wind models. As a result of the inclusion of optically thin clumps the radiative line force is increased compared to corresponding unclumped models, with a similar effect on either the mass-loss rate or the terminal velocity. When the clumps are allowed to be optically thick in continuum, on the other hand, the radiative force and consequently the mass-loss rate decreases alternatively.

scholarly journals Hot subdwarf wind models with accurate abundances

2019 ◽  
Vol 631 ◽  
pp. A75 ◽  
Author(s):  
J. Krtička ◽  
J. Janík ◽  
I. Krtičková ◽  
S. Mereghetti ◽  
F. Pintore ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Chemical Separation ◽  
The Other ◽  
Strong Wind ◽  
Radiative Force ◽  
Other Hand ◽  
Radiative Diffusion

Context. Hot subdwarfs are helium burning objects in late stages of their evolution. These subluminous stars can develop winds driven by light absorption in the lines of heavier elements. The wind strength depends on chemical composition which can significantly vary from star to star. Aims. We aim to understand the influence of metallicity on the strength of the winds of the hot hydrogen-rich subdwarfs HD 49798 and BD+18° 2647. Methods. We used high-resolution UV and optical spectra to derive stellar parameters and abundances using the TLUSTY and SYNSPEC codes. For derived stellar parameters, we predicted wind structure (including mass-loss rates and terminal velocities) with our METUJE code. Results. We derived effective temperature Teff = 45 900 K and mass M = 1.46 M⊙ for HD 49798 and Teff = 73 000 K and M = 0.38 M⊙ for BD+18° 2647. The derived surface abundances can be interpreted as a result of interplay between stellar evolution and diffusion. The subdwarf HD 49798 has a strong wind that does not allow for chemical separation and consequently the star shows solar chemical composition modified by hydrogen burning. On the other hand, we did not find any wind in BD+18° 2647 and its abundances are therefore most likely affected by radiative diffusion. Accurate abundances do not lead to a significant modification of wind mass-loss rate for HD 49798, because the increase of the contribution of iron and nickel to the radiative force is compensated by the decrease of the radiative force due to other elements. The resulting wind mass-loss rate Ṁ = 2.1 × 10−9 M⊙ yr−1 predicts an X-ray light curve during the eclipse which closely agrees with observations. On the other hand, the absence of the wind in BD+18° 2647 for accurate abundances is a result of its peculiar chemical composition. Conclusions. Wind models with accurate abundances provide more reliable wind parameters, but the influence of abundances on the wind parameters is limited in many cases.

scholarly journals A Rotating, Magnetic, Radiation-Driven Wind Model Applied to Be Stars

1987 ◽  
Vol 92 ◽  
pp. 437-439
Author(s):  
C. H. Poe ◽  
D. B. Friend
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Emission Lines ◽  
Be Stars ◽  
Wind Model ◽  
Low Velocity ◽  
Be Star ◽  
Open Magnetic Field

With their rotating, magnetic, radiation-driven wind model, Friend & MacGregor (1984) found that rapid rotation and an open magnetic field could enhance the mass loss rate (ṁ) and terminal velocity (V∞) in an 0 star wind. The purpose of this paper is to see if this model could help explain the winds from Be stars. The following features of Be star winds need to be explained: 1) Be stars exhibit linear polarization (Coyne & McLean 1982), indicating an enhanced equatorial density. 2) There appears to be enhanced mass loss (at low velocity) in the equatorial plane, from IRAS observations of Waters (1986). 3) The width of the broad Balmer emission lines remains unexplained.

Hot star wind mass-loss rate predictions at low metallicity

2018 ◽  
Vol 14 (S344) ◽  
pp. 208-210
Author(s):  
Jiří Krtička ◽  
Jiří Kubát
Keyword(s):  
Mass Loss ◽  
Mass Fraction ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Magnetic Line ◽  
Radiative Force ◽  
Line Profiles ◽  
Low Metallicity ◽  
Loss Rates

AbstractHot star winds are driven by the radiative force due to light absorption in lines of heavier elements. Therefore, the amount of mass lost by the star per unit of time, i.e., the mass-loss rate, is sensitive to metallicity. We provide mass-loss rate predictions for O stars with mass fraction of heavier elements 0.2 <Z/Z⊙ ≤ 1. Our predictions are based on global model atmospheres. The models allow us to predict wind terminal velocity and the mass-loss rate just from basic global stellar parameters. We provide a formula that fits the mass-loss rate predicted by our models as a function of stellar luminosity and metallicity. On average, the mass-loss rate scales with metallicity as (Z/Z⊙)0.59. The predicted mass-loss rates agree with mass-loss rates derived from ultraviolet wind line profiles. At low metallicity, the rotational mixing affects the wind mass-loss rates. We study the influence of magnetic line blanketing.

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 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 Radio observations and the mass flow rate of α Cyg (A2Ia)

1981 ◽  
Vol 59 ◽  
pp. 61-64
Author(s):  
B. Wolf ◽  
O. Stahl ◽  
W.J. Altenhoff
Keyword(s):  
Mass Loss ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Growth Analysis ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
The Other ◽  
Radio Flux ◽  
Radio Observations ◽  
Lower Mass

From the free-free excess at 10μ. Barlow and Cohen (1977) (hereafter referred to as BC) derived a mass loss rate of 6.9 10-7 M⊙ yr-1 for α Cyg. They predicted a 10 GHz radio flux of 2.2 mJy. On the other hand Praderie et al. (1980) derived a considerable lower mass loss rate of 1.1 10 -8 ≤Ṁ ≤ 7 10-8 M ⊙ yr-1 from a curve of growth analysis of the envelope ultraviolet Fell-lines of α Cyg. Radio observations are desirable to make a decision about these discrepant results. Therefore we observed α Cyg at 15 GHz with the 100 m telescope of the MPIfR at Effelsberg. The observations are discussed together with recent VLA data of Abbott et al. (1980).

scholarly journals Envelope Distention and Mass Loss IN W VIR Pulsating Variables

1989 ◽  
Vol 111 ◽  
pp. 262-262
Author(s):  
Yu. A. Fadeyev ◽  
H. Muthsam
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Stellar Atmosphere ◽  
Scale Height ◽  
The Other ◽  
Escape Velocity ◽  
Hydrodynamic Calculations ◽  
The Mean ◽  
Radial Pulsations

AbstractThe hydrodynamic calculations of nonlinear self-excited radial pulsations were done for the models of W Vir stars with mass 0.6 M⊙ and luminosities from 794L⊙ to 3981L⊙. The periods of the models are longer than 10 days. The pulsations are shown to be accompanied by periodic shocks that change the density distribution in the pulsating stellar atmosphere. At radii less than 5 Rph, where Rph is the radius of the photosphere, the mean dynamic scale height is nearly five times the static scale height. In this region of the atmosphere the mean radii of outer mass zones do not change perceptably. On the other hand, at radii larger than 5 Rph the scale height is of the order of Rph so that the outermost layers ultimately expand with a velocity exceeding the local escape velocity. The mass flux in the atmosphere increases with decreasing mass to radius ratio and mass loss rate in W Vir type variables is in the range from 2 X 10−6M⊙·yr−1 to 10−5M⊙·yr−1.

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 Spectroscopic Study of Pleione in 1977–1979

1982 ◽  
Vol 98 ◽  
pp. 161-165 ◽  
Author(s):  
Ryuko Hirata ◽  
Jun'ichi Katahira ◽  
Jun Jugaku
Keyword(s):  
Mass Loss ◽  
Spectroscopic Study ◽  
Shell Structure ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Radial Velocities ◽  
The Other

Shell spectra of Pleione in 1977–1979 are characterized by further increase in their strengths and by the development of the blue-winged profiles without noticeable variation of their radial velocities. The MgII resonance lines at λ2800A have the blue-shifted components with a velocity of-35 km/s relative to the other shell lines. The development of the shell structure is derived. The mass loss rate was 7×10−11 M⊙/yr.

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