Stellar winds and mass-loss rates from Be stars

1981 ◽  
Vol 251 ◽  
pp. 139 ◽  
Author(s):  
T. P., Jr. Snow
Keyword(s):  
Mass Loss ◽  
Stellar Winds ◽  
Be Stars ◽  
Loss Rates

scholarly journals Stellar Winds and Mass-Loss Rates from Be Stars

1982 ◽  
Vol 98 ◽  
pp. 377-385 ◽  
Author(s):  
Theodore P. Snow
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Stellar Winds ◽  
Be Stars ◽  
Line Profiles ◽  
Sample Group ◽  
Show Evidence ◽  
Acceleration Zone ◽  
Low Levels ◽  
Loss Rates

Resonance-line profiles of SiIII and SiIV lines in 22 B and Be stars have been analyzed in the derivation of mass-loss rates. Of the 19 known Be or shell stars in the sample group, all but one show evidence of winds. It is argued that for stars of spectral type B1.5 and later, SiIII and SiIV are the dominant stages of ionization, and this conclusion, together with theoretical fits to the line profiles, leads to mass-loss rates between 10-11 and 3 × 10-9 for the stars. The rate of mass loss does not correlate simply with stellar parameters, and probably is variable with time. The narrow FeIII shell lines often seen in the ultraviolet spectra of Be stars may arise at low levels in the wind, below the strong acceleration zone. The mass-loss rates from Be stars are apparently insufficient to affect stellar evolution.

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.

scholarly journals The Relation Between Mass Loss and Luminosity For Be Stars

1987 ◽  
Vol 92 ◽  
pp. 245-249
Author(s):  
L.B.F.M. Waters ◽  
H.J.G.L.M. Lamers ◽  
J. Coté
Keyword(s):  
Mass Loss ◽  
Mass Flux ◽  
Polar Regions ◽  
Be Stars ◽  
Large Sample ◽  
Disc Model ◽  
Mass Fluxes ◽  
Loss Rates

AbstractThe mass loss rates of a large sample of Be stars derived from the UV and the IR are compared. The IR rates were derived using a simple equatorial disc model, and are typically a factor 100 larger than those derived from the UV. In terms of mass fluxes, the mass flux in the polar regions (derived from the UV observations) is about a factor 103 smaller than the mass flux in the equatorial regions. The dependence of MIR and Muv on stellar luminosity is studied. It is shown that MIR depends weaker on L than Muv. This suggests that two different mechanisms are responsible for the mass flux in polar and equatorial regions.

scholarly journals Evidence for Mass Loss at Polar Latitudes in ω Ori and 66 Oph

1982 ◽  
Vol 98 ◽  
pp. 401-404
Author(s):  
Geraldine J. Peters
Keyword(s):  
Mass Loss ◽  
High Velocity ◽  
Be Stars ◽  
Loss Rates

IUE observations of the “pole-on” Be stars ω Ori and 66 Oph have revealed the unexpected presence of high velocity (v ≃ −750 km s−1), relatively narrow (Δλ ≃ 1A) absorption components in the resonance lines of C IV, Si III, and Si IV. The C IV features show structure indicative of multiple shells or clouds. Similar high velocity lines were not observed in other pole-on Be stars considered in the program. The nature of these unusual features and the column densities and mass loss rates implied by them are discussed in this paper.

scholarly journals Chemical enrichment from Wolf-Rayet stellar winds

1999 ◽  
Vol 193 ◽  
pp. 218-226
Author(s):  
Georges Meynet
Keyword(s):  
Angular Velocity ◽  
Interstellar Medium ◽  
Mass Loss ◽  
Solar Nebula ◽  
Cosmic Ray ◽  
Stellar Winds ◽  
Chemical Enrichment ◽  
Galactic Cosmic Ray ◽  
Loss Rates

Stellar winds contribute together with supernovae explosions to the chemical enrichment of the interstellar medium. We recall how the metallicity dependence of the stellar winds implies a metallicity dependence of the stellar yields. We show that an increase of the initial angular velocity has different effects than an increase of the mass loss rates. Wolf-Rayet stars appear as important sources of 19F and 26Al. They are the favoured candidates for the 22Ne anomaly observed in the Galactic cosmic ray sources. They may also have injected into the proto-solar nebula short-lived radionuclides as 26Al, 36Cl, 41Ca, 107Pd and 205Pb.

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 Interacting stellar winds in a binary system

1981 ◽  
Vol 59 ◽  
pp. 499-502
Author(s):  
Sun Kwok
Keyword(s):  
Binary System ◽  
Mass Loss ◽  
Stellar Winds ◽  
Long Time ◽  
Wind Velocities ◽  
M Stars ◽  
Hr Diagram ◽  
Loss Rates

It is now known that strong stellar winds develop in stars mostly at the red and blue sides of the HR diagram. However, although the mass loss rates observed in O and M stars are comparable, the corresponding wind velocities are vastly different. It would thus be of great interest to find a binary system, containing both a cool and a hot star each with its own wind, and observe the resultant interaction. For a long time, α Sco (M1.5 Iab + B2.5 V) was the only known example (Kudritzki and Reimers 1978, van der Hucht et al. 1980). The situation in this case is best illustrated by a VLA map made by Gibson (1979) who finds that a shock develops at the surface of interaction of the two winds. In this paper I shall describe another binary system in which two stellar winds are interacting with dramatic effects.

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