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 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 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.

Preliminary Observations of Interstellar Sodium D-Line Absorption towards the Carina Nebula

1980 ◽  
Vol 4 (1) ◽  
pp. 95-97 ◽  
Author(s):  
J. B. Whiteoak ◽  
F. F. Gardner
Keyword(s):  
High Resolution ◽  
Hii Regions ◽  
Early Type ◽  
Interstellar Clouds ◽  
Carina Nebula ◽  
Line Absorption ◽  
General Investigation ◽  
Early Type Stars ◽  
Resolution Study

As part of a general investigation of interstellar clouds associated with southern HII regions we have begun a high-resolution study of the sodium D-line absorption in the directions of early-type stars that are likely to be associated with or located behind the clouds.

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 The VLT-FLAMES survey of massive stars: mass loss and rotation of early-type stars in the SMC

2006 ◽  
Vol 456 (3) ◽  
pp. 1131-1151 ◽  
Author(s):  
M. R. Mokiem ◽  
A. de Koter ◽  
C. J. Evans ◽  
J. Puls ◽  
S. J. Smartt ◽  
...  
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Early Type ◽  
Early Type Stars

scholarly journals A Comparison of Luminosity Calibrations for MK Classifications of OB Stars

1979 ◽  
Vol 47 ◽  
pp. 81-86
Author(s):  
Janet Rountree Lesh
Keyword(s):  
Main Sequence ◽  
Early Type ◽  
Class V ◽  
Ob Stars ◽  
Early Type Stars

It has been apparent for some time that there is a need for a single luminosity calibration to be used with modern MK types for early-type stars, at least from 0 through middle B. The widely used calibration of Blaauw (1963) has to be replaced because the refinement of the MK system - as reflected in the large collections of spectral types by Lesh (1968), Hiltner, Garrison, and Schild (1969) and Walborn (1971) - has led to a lower mean luminosity for most main sequence subgroups of early-type stars, as the higher luminosity stars tend to move out of class V. Thus the calibrations of Lesh (1968) and Walborn (1972, 1973) are systematically fainter than Blaauw’s

VLA radio continuum measurements of mass loss from early-type stars

1980 ◽  
Vol 238 ◽  
pp. 196 ◽  
Author(s):  
D. C. Abbott ◽  
J. H. Bieging ◽  
E. Churchwell ◽  
J. P. Cassinelli
Keyword(s):  
Mass Loss ◽  
Radio Continuum ◽  
Early Type ◽  
Early Type Stars
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