Periodic Variations and Mass Loss in Be Stars

1994 ◽  
pp. 287-298 ◽  
Author(s):  
Hideyuki Saio
Keyword(s):  
Mass Loss ◽  
Be Stars

scholarly journals Non-radial Pulsations of BA Supergiants and Be Stars

1999 ◽  
Vol 169 ◽  
pp. 312-319
Author(s):  
Dietrich Baade
Keyword(s):  
Mass Loss ◽  
Background Noise ◽  
The Other ◽  
Be Stars ◽  
Physical Processes ◽  
Other Hand ◽  
Be Star ◽  
The Subject ◽  
Radial Pulsations

If observing time and number of photons are not the limit, it will probably be very difficult to find any Be star or BA supergiant that is not variable. Moreover, there is hardly any major set of observations that is not tempting to explain at least partly in terms of nonradial (g-mode) pulsations. Since a few years ago, such conjectures are also theoretically permissible because improved opacity calculations have established the classical к-mechanism as a viable source of pulsation driving (cf. Pamyatnykh, these proceedings).Contrary to Be stars, it can for any given BA supergiant nevertheless be arbitrarily difficult to diagnose nonradial pulsations (NRP’s) with certainty because they need to be detected against considerable background ‘noise’ of other physical processes, most of which are related to mass loss and/or rotation. To make things worse, there is some evidence that NRP’s can have some effect on the dynamics of the mass loss. On the other hand, variable and non-spherical winds is the subject of this Colloquium, and this paper is accordingly biased towards the interplay between pulsation and mass loss.

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.

Steady-State Mass Loss for be Stars

1974 ◽  
Vol 192 ◽  
pp. 429 ◽  
Author(s):  
D. Nelson Limber
Keyword(s):  
Steady State ◽  
Mass Loss ◽  
Be Stars

Evidence for mass loss in the mid-ultraviolet spectra of Be stars

1977 ◽  
Vol 216 ◽  
pp. 457 ◽  
Author(s):  
T. H. Morgan ◽  
J. L. Modisette ◽  
Y. Kondo
Keyword(s):  
Mass Loss ◽  
Be Stars ◽  
Ultraviolet Spectra

Evidence for mass loss at moderate to high velocity in Be stars

1976 ◽  
Vol 203 ◽  
pp. L87 ◽  
Author(s):  
T. P., Jr. Snow ◽  
J. M. Marlborough
Keyword(s):  
Mass Loss ◽  
High Velocity ◽  
Be Stars

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 Pulsations of Be stars: time series analysis of He I λ4921

1994 ◽  
Vol 162 ◽  
pp. 100-101
Author(s):  
M. E. Hahula ◽  
D. R. Gies
Keyword(s):  
Time Series ◽  
Time Series Analysis ◽  
Mass Loss ◽  
Power Spectra ◽  
Phase Content ◽  
Be Stars ◽  
Optical Photometry ◽  
Multi Wavelength ◽  
Spectroscopy Optical ◽  
Nonradial Pulsation

We present the results of time series observations of He I λ4921 in the spectra of 10 Be stars. The spectra were obtained during multi-wavelength campaigns of IUE spectroscopy, optical photometry and polarimetry, and spectroscopy undertaken to study the connection (if any) between nonradial pulsation (NRP) and mass loss in Be stars. Power spectra have been calculated for the time series of intensity variations within the profiles. These were used to determine periodic variability and phase content to analyze the variations in the context of the NRP model. The observations were made at three observatories (Table 1). All the spectra record at least Hβ and He I λ4921 with a S/N > 200 per pixel and a resolution of ≈ 0.2 Å. We have concentrated the analysis on He I λ4921 as a probe of photospheric variability. This line is generally free of emission (unlike He I λ6678), but in some cases an Fe II λ4924 shell component appears in the red wing.

scholarly journals Simultaneous Spectroscopy and Polarimetry of Be Stars

1987 ◽  
Vol 92 ◽  
pp. 84-86
Author(s):  
D. R. Gies ◽  
David McDavid
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Absorption Line ◽  
Line Profile ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Line Profiles ◽  
Initial Attempt ◽  
Rapid Variability ◽  
Hα Emission

Evidence is now accumulating that many Be stars display photospheric line profile variations on timescales of days or less that are probably caused by nonradial pulsations (Baade 1984; Penrod 1986). In some circumstances these pulsations can promote mass loss into the circumstellar envelope, and consequently the conditions in the inner part of the envelope may vary on similar timescales. Changes in the envelope could produce variations in the polarization and emission line profiles, and observers have reported rapid variability in both. We describe here an initial attempt to search for simultaneous variations in continuum polarization, Hα emission, and the He I λ6678 photospheric absorption line in order to investigate correlated changes on short timescales.

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