scholarly journals The dependence of mass loss on the basic stellar parameters

1981 ◽  
Vol 59 ◽  
pp. 19-25
Author(s):  
Henny J.G.L.M. Lamers
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Radio Flux ◽  
Wind Model ◽  
Infrared Excess ◽  
B Stars ◽  
Radio Data ◽  
Hα Emission ◽  
Loss Rates

We determined the dependence of mass loss on the stellar parameters for O and B stars of various luminosities. We used four homogenous sets of mass loss rates derived by different authors from the radioflux, the infrared excess, the UV lines and Hα emission. As the rates derived from the radio flux are the least dependent on model assumptions for the stellar wind, these will be adopted as our standards. The others sets of mass loss rates will be corrected for the differences in the adopted wind model, especially in the velocity law, by scaling the rates to those derived from radio data, using the stars which the different sets have in common.

scholarly journals Evolution of O stars and the WR connection

1979 ◽  
Vol 83 ◽  
pp. 431-445 ◽  
Author(s):  
Peter S. Conti
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
High Luminosity ◽  
Loss Mechanism ◽  
Evolutionary Scenario ◽  
Processed Material ◽  
Dominant Process ◽  
Highly Evolved ◽  
Loss Rates ◽  
Enriched Composition

The stellar wind mass loss rates of at least some single Of type stars appear to be sufficient to remove much if not all of the hydrogen-rich envelope such that nuclear processed material is observed at the surface. This highly evolved state can then be naturally associated with classic Population I WR stars that have properties of high luminosity for their mass, helium enriched composition, and nitrogen or carbon enhanced abundances. If stellar wind mass loss is the dominant process involved in this evolutionary scenario, then stars with properties intermediate between Of and WR types should exist. The stellar parameters of luminosity, temperature, mass and composition are briefly reviewed for both types. All late WN stars so far observed are relatively luminous like Of stars, and also contain hydrogen. All early WN stars, and WC stars, are relatively faint and contain little or no hydrogen. The late WN stars seem to have the intermediate properties required if a stellar wind is the dominant mass loss mechanism that transforms an Of star to a WR type.

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.

Empirical mass-loss rates for 25 O and early B stars, derived from Copernicus observations

1981 ◽  
Vol 247 ◽  
pp. 173 ◽  
Author(s):  
R. Gathier ◽  
H. J. G. L. M. Lamers ◽  
T. P. Snow
Keyword(s):  
Mass Loss ◽  
B Stars ◽  
Loss Rates

scholarly journals Clumping-corrected mass-loss rates of Wolf-Rayet stars: comparison with the optically thick wind model

1999 ◽  
Vol 193 ◽  
pp. 84-85
Author(s):  
Tiit Nugis
Keyword(s):  
Mass Loss ◽  
Energy Supply ◽  
Wind Model ◽  
Loss Rates

Clumping-corrected mass-loss rates of Wolf-Rayet stars lie in the range 0.2–10 x 10−5 M⊙ yr−1. It was found that optically thick wind models can lead to the observed mass-loss rates of WR stars at certain energy supply conditions in the subsonic zone.

Mass Loss and Stellar Wind in Massive X-Ray Binaries

1980 ◽  
Vol 5 ◽  
pp. 541-547
Author(s):  
H. F. Henrichs
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Binary Systems ◽  
Massive Stars ◽  
Compact Star ◽  
X Rays ◽  
Early Type ◽  
X Ray ◽  
X Ray Binaries ◽  
Loss Rates

A number of massive stars of early type is found in X-ray binary systems. The catalog of Bradt et al. (1979) contains 21 sources optically identified with massive stars ranging in spectral type from 06 to B5 out of which 13 are (nearly) unevolved stars and 8 are supergiants. Single stars of this type generally show moderate to strong stellar winds. The X-rays in these binaries originate from accretion onto a compact companion (we restrict the discussion to this type of X-rays).We consider the compact star as a probe traveling through the stellar wind. This probe enables us to derive useful information about the mass outflow of massive stars.After presenting the basic data we derive an upper limit to mass loss rates of unevolved early type stars by studying X-ray pulsars. Next we consider theoretical predictions concerning the influence of X-rays on the stellar wind and compare these with the observations. Finally, using new data from IUE, we draw some conclusions about mass loss rates and velocity laws as derived from X-ray binaries.

scholarly journals Corrections for Hydrostatic Atmospheric Models: Radii and Effective Temperatures of Wolf Rayet Stars

1982 ◽  
Vol 99 ◽  
pp. 53-56 ◽  
Author(s):  
C. De Loore ◽  
P. Hellings ◽  
H.J.G.L.M. Lamers
Keyword(s):  
Mass Loss ◽  
Optical Depth ◽  
Stellar Wind ◽  
Theoretical Models ◽  
Roche Lobe ◽  
Evolutionary Models ◽  
Atmospheric Models ◽  
Helium Burning ◽  
Effective Temperatures ◽  
Loss Rates

With the assumption of planparallel hydrostatic atmospheres, used generally for the computation of evolutionary models, the radii of WR stars are seriously underestimated. The true atmospheres may be very extended, due to the effect of the stellar wind. Instead of these hydrostatic atmospheres we consider dynamical atmospheres adopting a velocity law. The equation of the optical depth is integrated outwards using the equation of continuity.The “hydrostatic” radii are to be multiplied with a factor 2 to 8, and the effective temperatures with a factor 0.8 to 0.35 when Wolf Rayet characteristics for the wind are considered, and WR mass loss rates are used. With these corrections the effective temperatures of the theoretical models, which are helium burning Roche lobe overflow remnants, range between 30 000 K and 50 000 K. Effective temperatures calculated in the hydrostatic hypothesis can be as high as 150 000 K for helium burning RLOF-remnants with WR mass loss rates.

scholarly journals Infrared spectroscopy of Be stars

1994 ◽  
Vol 162 ◽  
pp. 412-413
Author(s):  
R.M. Torres ◽  
A. Damineli-Neto ◽  
J.A. de Freitas Pacheco
Keyword(s):  
Mass Loss ◽  
Near Infrared ◽  
Uv Spectra ◽  
Emission Lines ◽  
Be Stars ◽  
B Stars ◽  
Astrophysical Objects ◽  
Optical Region ◽  
Support Excitation ◽  
Loss Rates

FeII emission lines are present in a variety of astrophysical objects and, in particular, in Be stars, where in some situations they can also be seen in absorption. Selvelli & Araujo (1984) studied a sample of classical Be stars that have FeII emission lines in the optical region. The analysis of IUE spectra of those stars revealed that, for the majority of the objects, neither absorption nor emission FeII features were present in the UV. The conclusion was that their data could not support excitation of FeII by continuum fluorescence. On the other hand, FeIII of circumstellar origin is often seen in absorption in the UV spectra of Be stars (Snow & Stalio 1987 and references therein). This could be an indication that the optical FeII emission lines are originated from recombination and cascade. However, Selvelli & Araujo (1984) argued that, since the multiplet UV 191 of FeII does not appear in emission, that mechanism is probably not relevant. In the present work we report new spectroscopic observations in the near infrared of a sample of 60 Be stars, including the prominent FeII 999.7 nm emission line. This line is also present in the spectra of superluminous B stars for which mass loss rates have recently been estimated (Lopes, Damineli-Neto & Freitas Pacheco 1992). We derived mass loss rates from the infrared line luminosities, in agreement with those derived by other methods. We also found a new evidence of the Be envelope flattening through the FeII/Paδ line ratio.

scholarly journals The Wind-Compressed Disk Model

1994 ◽  
Vol 162 ◽  
pp. 455-468
Author(s):  
J.E. Bjorkman
Keyword(s):  
Mass Loss ◽  
Threshold Value ◽  
Be Stars ◽  
Disk Model ◽  
Disk Formation ◽  
Hα Emission ◽  
Effects Of Rotation ◽  
Acceleration Of Gravity ◽  
Ionization Balance ◽  
Loss Rates

We discuss the effects of rotation on the structure of radiatively-driven winds. When the centrifugal support is large, there is a region, at low latitudes near the surface of the star, where the acceleration of gravity is larger than the radiative acceleration. Within this region, the fluid streamlines “fall” toward the equator. If the rotation rate is large, this region is big enough that the fluid from the northern hemisphere collides with that from the southern hemisphere. This produces standing shocks above and below the equator. Between the shocks, there is a dense equatorial disk that is confined by the ram pressure of the wind. A portion of the flow that enters the disk proceeds outward along the equator, but the inner portion accretes onto the stellar surface. Thus there is simultaneous outflow and infall in the equatorial disk. The wind-compressed disk forms only if the star is rotating faster than a threshold value, which depends on the ratio of wind terminal speed to stellar escape speed. The spectral type dependence of the disk formation threshold may explain the frequency distribution of Be stars. Observational tests of the wind-compressed disk model indicate that, although the geometry of the disk agrees with observations of Be stars, the density is a factor of 100 too small to produce the IR excess, Hα emission, and optical polarization, if current estimates of the mass-loss rates are used. However, recent calculations of the ionization balance in the wind indicate that the mass-loss rates of Be stars may be significantly underestimated.

scholarly journals Mass-loss Rates for O and Early B Stars Powering Bow Shock Nebulae: Evidence for Bistability Behavior

2019 ◽  
Vol 158 (2) ◽  
pp. 73 ◽  
Author(s):  
Henry A. Kobulnicky ◽  
William T. Chick ◽  
Matthew S. Povich
Keyword(s):  
Mass Loss ◽  
Bow Shock ◽  
B Stars ◽  
Loss Rates
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