scholarly journals The velocity characteristics of WR stellar winds

1981 ◽  
Vol 59 ◽  
pp. 27-33
Author(s):  
Allan J. Willis
Keyword(s):  
Mass Loss ◽  
Mean Value ◽  
Stellar Winds ◽  
Temperature Structure ◽  
Early Type ◽  
Ob Stars ◽  
Stellar Photosphere ◽  
The Mean ◽  
Early Type Stars ◽  
Resonance Transitions

The stellar winds of hot early-type stars are characterised spectroscopically by the presence of P-Cygni profiles, which are most marked for resonance transitions of common ions and generally occur in the UV, and typical resonance lines of SiIV, CIV, NV and OVI are well known P-Cygni signatures of stellar winds in luminous OB stars. Analyses of these profiles can lead to important information concerning the velocity, density and temperature structure of such winds. The WR stars have more developed stellar winds than OB stars, supporting higher particle densities at larger distances from the stellar “photosphere”. Recently Barlow, Smith & Willis, hereinafter BSW, (1980), have derived reliable mass loss rates for 21 WR stars. The mean value is 4x10-5 M0 /y and the rates are considerably larger than can be accomodated by soley radiative models. The, as yet unidentified, mechanism initiating the WR mass loss may also be important for Of stars ( Lamers 1980 ).

scholarly journals Terminal Velocities for a Large Sample of O Stars, B Supergiants, and Wolf-Rayet Stars

1991 ◽  
Vol 143 ◽  
pp. 317-317
Author(s):  
R. K. Prinja ◽  
M. J. Barlow ◽  
I. D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Early Type ◽  
Nuclear Mass ◽  
Ob Stars ◽  
Residual Intensity ◽  
The Mean ◽  
Effective Temperatures ◽  
Early Type Stars ◽  
Absorption Features

We argue that easily measured, reliable estimates of terminal velocities for early-type stars are provided (1) by the central velocity asymptotically approached by narrow absorption features in unsaturated UV P Cygni profiles, and (2) by the violet limit of zero residual intensity in saturated P Cygni profiles. We use these estimators and high resolution IUE data to determine terminal velocities, v∞, for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OB stars our values are typically 15-20% smaller than the extreme violet edge velocities, vedge, while for WR stars v∞ = 0.76vedge on average. We give new mass-loss rates for WR stars which are thermal radio emitters, taking into account our new terminal velocities and recent revisions to estimates of distances and to the mean nuclear mass per electron. We examine the relationships between v∞, the surface escape velocities, and effective temperatures.

scholarly journals Mass loss from early-type stars

1970 ◽  
Vol 36 ◽  
pp. 209-212
Author(s):  
J. B. Hutchings
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Stellar Evolution ◽  
Early Type ◽  
High Luminosity ◽  
Spectroscopic Evidence ◽  
Ob Stars ◽  
Early Type Stars ◽  
Very High ◽  
Hr Diagram

Following the detailed study of four very high luminosity OB stars, a survey has been made for spectroscopic evidence of mass loss in a number of early-type supergiants. A list of spectroscopic criteria is given and the mass loss estimates for 24 stars plotted on the HR diagram. The dependence of the phenomenon on spectral type and luminosity is discussed as well as its significance in terms of stellar evolution.

scholarly journals Mass loss rates of OB stars derived from infrared observations

1981 ◽  
Vol 59 ◽  
pp. 51-56 ◽  
Author(s):  
E.G. Tanzi ◽  
M. Tarenghi ◽  
N. Panagia
Keyword(s):  
Mass Loss ◽  
Near Infrared ◽  
Broad Band ◽  
Early Type ◽  
Model Calculations ◽  
Infrared Observations ◽  
Ob Stars ◽  
Wide Range ◽  
Early Type Stars ◽  
Loss Rates

In this paper we report briefly on a study of the mass loss of early type stars in the infrared. Up to now near infrared (1.25 - 4.8 μ ) broad band photometry of 70 southern OB stars of various luminosity class has been secured. Program stars have been selected, among those bright enough in the infrared to give a suitable photometric accuracy, in order to cover a wide range of spectral types (Fig. 1).37 stars are found to exhibit emission in excess over a blackbody photospheric continuum, which is interpreted in terms of gas ejected in the form of an accelerated wind. By means of model calculations the corresponding mass loss rates are derived. The obtained values compare well with those determined indipendently by various Authors for stars in common. Our data show that mass loss rates increase with luminosity and are a decreasing function of surface gravity.

scholarly journals High-Energy Phenomena in Be Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 250-262 ◽  
Author(s):  
Theodore P. Snow
Keyword(s):  
General Property ◽  
Review Paper ◽  
High Energy ◽  
Early Years ◽  
Stellar Winds ◽  
Be Stars ◽  
Early Type ◽  
Ob Stars ◽  
Early Type Stars

It was discovered in the early years of the Copernicus satellite operations that the stellar winds in early-type stars are often characterized by degrees of ionization inconsistent with the spectral types of the stars. The most notable early example was the discovery of strong OVI lines in the form of P Cygni profiles in stars too cool to have this ion in their photospheres, such as τ SCO (BOV; Rogerson and Lamers 1975). Systematic studies showed that excess ionization is a general property of the winds in OB stars (e.g. Lamers and Snow 1978).

scholarly journals The Metallicity Dependence of the Mass Loss of Early-Type Massive Stars

2007 ◽  
Vol 3 (S250) ◽  
pp. 39-46
Author(s):  
Alex de Koter
Keyword(s):  
Mass Loss ◽  
Metal Content ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Stellar Winds ◽  
Early Type ◽  
The Galaxy ◽  
Early Type Stars ◽  
Good Agreement ◽  
Comprehensive Study

AbstractWe report on a comprehensive study of the wind properties of 115 O- and early B-type stars in the Galaxy and the Large Magellanic Clouds. This work is part of the VLT/FLAMES Survey of Massive Stars. The data is used to construct the empirical dependence of the mass-loss in stellar winds on the metal content of their atmospheres. The metal content of early-type stars in the Magellanic Clouds is discussed. Assuming a power-law dependence of mass loss on metal content, Ṁ ∝ Zm, we find m = 0.83 ± 0.16 from an analysis of the wind momentum luminosity relation (Mokiem et al. 2007b). This result is in good agreement with the prediction m = 0.69 ± 0.10 by Vink et al. (2001). Though the scaling agrees, the absolute empirical value of mass loss is found to be a factor of two higher than predictions. This may be explained by a modest amount of clumping in the outflows of the objects studied.

scholarly journals Radiative wind acceleration in early type stars

1981 ◽  
Vol 59 ◽  
pp. 173-178 ◽  
Author(s):  
N. Panagia ◽  
F. Macchetto
Keyword(s):  
Observational Data ◽  
Effective Temperature ◽  
Single Scattering ◽  
Terminal Velocity ◽  
Stellar Winds ◽  
Early Type ◽  
Photon Scattering ◽  
Ob Stars ◽  
Early Type Stars ◽  
Radiative Acceleration

AbstractThe processes of radiative acceleration of stellar winds in OB stars by single and multiple photon scattering are considered. Single scattering can be the dominant accelerating process for stars later than B2 (Teff < 2 x 104 K) and can account for terminal velocities up to 500 – 1000 km s-1 . Multiple scattering of photons in the approximate range 200 – 500 A provides additional wind acceleration for stars earlier than B2 to reach terminal velocities of up to 2000 – 4000 km s-1 A systematic increase of the terminal velocity as a function of the effective temperature is predicted. Observational data confirm this expectation quite well.

scholarly journals The properties of early-type stars in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 325-336
Author(s):  
Christopher J. Evans
Keyword(s):  
Physical Properties ◽  
Mass Loss ◽  
Temperature Scale ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Early Type ◽  
The Past ◽  
The Galaxy ◽  
Stellar Temperature ◽  
Early Type Stars

AbstractThe past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.

scholarly journals New Results on Pulsating OB Stars

1995 ◽  
Vol 155 ◽  
pp. 44-55 ◽  
Author(s):  
Paweł Moskalik
Keyword(s):  
Data Model ◽  
Physical Mechanism ◽  
High Order ◽  
Early Type ◽  
Instability Strip ◽  
Model Calculations ◽  
B Stars ◽  
Ob Stars ◽  
Early Type Stars ◽  
Theoretical Results

AbstractUntil very recently the physical mechanism driving oscillations in β Cep and other early type stars has been a mystery. The breakthrough came with the publication of new OPAL and OP opacity data. Model calculations with the new opacities have demonstrated that the pulsations are driven by the familiar K-mechanism, acting in the metal opacity bump at T ≈ 2 × 105K. The mechanism excites the low order p- and g-modes in the upper part of the instability strip and the high order g-modes in the lower part of the strip. The theoretical instability domains agree well with the observed domains of the β Cep and the SPB stars. In this review I present these recent theoretical results and discuss their consequences for our understanding of B stars pulsations.

scholarly journals What Do We Really Know About the Winds of Massive Stars?

2007 ◽  
Vol 3 (S250) ◽  
pp. 89-96
Author(s):  
D. John Hillier
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Standard Theory ◽  
Stellar Winds ◽  
X Rays ◽  
X Ray ◽  
Stellar Photosphere ◽  
Weak Winds ◽  
Ionization Balance ◽  
Loss Rates

AbstractThe standard theory of radiation driven winds has provided a useful framework to understand stellar winds arising from massive stars (O stars, Wolf-Rayet stars, and luminous blue variables). However, with new diagnostics, and advances in spectral modeling, deficiencies in our understanding of stellar winds have been thrust to the forefront of our research efforts. Spectroscopic observations and analyses have shown the importance of inhomogeneities in stellar winds, and revealed that there are fundamental discrepancies between predicted and theoretical mass-loss rates. For late O stars, spectroscopic analyses derive mass-loss rates significantly lower than predicted. For all O stars, observed X-ray fluxes are difficult to reproduce using standard shock theory, while observed X-ray profiles indicate lower mass-loss rates, the potential importance of porosity effects, and an origin surprisingly close to the stellar photosphere. In O stars with weak winds, X-rays play a crucial role in determining the ionization balance, and must be taken into account.

scholarly journals Clumps in stellar winds

2014 ◽  
Vol 1 ◽  
pp. 39-41 ◽  
Author(s):  
J. S. Vink
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Stellar Winds ◽  
Present Evidence ◽  
Close Proximity ◽  
Stellar Photosphere ◽  
Loss Rates

Abstract. We discuss the origin and quantification of wind clumping and mass–loss rates (Ṁ), particularly in close proximity to the Eddington (Γ) limit, relevant for very massive stars (VMS). We present evidence that clumping may not be the result of the line-deshadowing instability (LDI), but that clumps are already present in the stellar photosphere.

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