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.

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 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 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 Periodic Variations and Mass Loss in Be Stars

1994 ◽  
Vol 162 ◽  
pp. 287-298 ◽  
Author(s):  
Hideyuki Saio
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Mass Loss Rate ◽  
Rotation Period ◽  
Be Stars ◽  
Surface Magnetic Field ◽  
Upper Limit ◽  
Short Period ◽  
Angular Momentum Loss ◽  
Be Star

We discuss the connection between the periodic light variations and the equatorial mass loss of Be stars. The observed properties of the short period (~ day) variations seem to indicate that they arise in the photosphere. An upper limit for the surface magnetic field of Be stars is derived from the rate of angular momentum loss expected from the typical mass loss-rate in Be stars. The upper limit suggests that surface magnetic fields of Be stars are too weak to make a spot. We argue that the periodic variations of Be stars are explained by nonradial pulsations whose periods on the stellar surface are much longer than the rotation period. They transport angular momentum from the core to the envelope to accelerate the surface regions. If this mechanism works sufficiently well, the rotation speed near the surface will reach to the critical velocity and an excretion disk will be formed around the star. A simple model for a steady-state excretion disk around a Be star is found to be consistent with the density structure inferred from the IR fluxes.

scholarly journals Delta-slow solution to explain B supergiant stars' winds

2014 ◽  
Vol 9 (S307) ◽  
pp. 104-105
Author(s):  
M. Haucke ◽  
I. Araya ◽  
C. Arcos ◽  
M. Curé ◽  
L. Cidale ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Radiation Force ◽  
Terminal Velocity ◽  
Radiative Transport ◽  
Synthetic Spectra ◽  
Transport Code ◽  
Fast Solution ◽  
Good Agreement

AbstractA new radiation-driven wind solution called δ-slow was found by Curé et al. (2011) and it predicts a mass-loss rate and terminal velocity slower than the fast solution (m-CAK, Pauldrach et al. 1986). In this work, we present our first synthetic spectra based on the δ-slow solution for the wind of B supergiant (BSG) stars. We use the output of our hydrodynamical code HYDWIND as input in the radiative transport code FASTWIND (Puls et al. 2005). In order to obtain stellar and wind parameters, we try to reproduce the observed Hα, Hβ, Hγ, Hδ, Hei 4471, Hei 6678 and Heii 4686 lines. The synthetic profiles obtained with the new hydrodynamical solutions are in good agreement with the observations and could give us clues about the parameters involved in the radiation force.

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 The fraction of O-type supergiants in our galaxy in the LMC and in the SMC: an evidence of the correlation between mass loss rate and chemical abundance

1981 ◽  
Vol 59 ◽  
pp. 255-259
Author(s):  
G.F. Bisiacchi ◽  
C. Firmani
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Galactic Center ◽  
Mass Loss Rate ◽  
Relative Number ◽  
The Other ◽  
Be Stars ◽  
Chemical Abundance ◽  
Low Gravity ◽  
Hydrogen Burning

The distribution of the spectral types of the WR stars in our galaxy is different at different distances from the galactic center. This distribution is also different in all three galaxies, in our, in the LMC and in the SMC. These results have been interpreted as due to the dependence of the mass loss rate from the original chemical abundace which is known to be different in these objects.On the other hand it has been proposed by Chiosi et al. (1974) and confirmed by Bisiacchi et al. (1978) that most of the 0 supergiants should be stars in the hydrogen burning phase. These authors also find evidence that the large relative number of supergiants among th 0 and early B type stars must be related to the longer time spent by the evolutionary tracks with mass loss at the low gravity region. Recently, a new empirical formula has been proposed by Chiosi (1980) for the mass loss rate as function of the luminosity and temperature of the stars.

scholarly journals Wind characteristics of the 07 n star HD 217086 in the Cep OB 3 association

1981 ◽  
Vol 59 ◽  
pp. 41-44
Author(s):  
Mario Perinotto ◽  
Nino Panagia
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Uv Spectra ◽  
H Ii Region ◽  
Wind Characteristics

AbstractThe 07 n star HD 217086 which provides the ionization of the H II region S 155 A and is the brightest member of the Cep OB 3 association, has been observed in the ultraviolet with IUE. From an analysis of the UV spectra we determine a terminal velocity of 3560 ± 100 km s-1 and a mass loss rate of . A comparison is made with the stars of similar spectral type.

scholarly journals On the Equatorial Mass-Loss Rate of Be Stars

2002 ◽  
Vol 185 ◽  
pp. 520-521
Author(s):  
A.T. Okazaki
Keyword(s):  
Mass Loss ◽  
Formation Process ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Be Stars ◽  
Disk Model ◽  
Disk Formation

AbstractWe numerically study the formation process of equatorial disks around isolated Be stars, using an SPH code. We find that the viscous decretion disk model naturally explains the observed disk formation episode of X Per, giving the equatorial mass-loss rate of several ×10−9 (ρ0/10−10 g cm−3) M⊙ yr−1, where ρ0 is the base density of the disk.

Sign in / Sign up

Export Citation Format

Share Document