The Possible Role of Radiative Acceleration in Supporting Extended Atmospheres in Be Stars

1976 ◽  
pp. 377-382
Author(s):  
R. L. Kurucz ◽  
R. E. Schild
Keyword(s):  
Be Stars ◽  
Radiative Acceleration

scholarly journals The Possible Role of Radiative Acceleration in Supporting Extended Atmospheres in Be Stars

1976 ◽  
Vol 70 ◽  
pp. 377-382 ◽  
Author(s):  
R. L. Kurucz ◽  
R. E. Schild
Keyword(s):  
Effective Temperature ◽  
Detailed Calculation ◽  
Be Stars ◽  
Be Star ◽  
Hα Emission ◽  
Two Peaks ◽  
Radiative Acceleration ◽  
Emission Strength ◽  
Peaked Function

A detailed calculation of the radiative acceleration in B-type stars shows it to be a double-peaked function of effective temperature at small optical depths. The two peaks are shown to coincide approximately with peaks in the distribution of mean Hα emission strength as a function of B - V color in Be stars. These facts suggest that radiation may play an important role in the support of the Be star extended atmosphere.

scholarly journals The role of radiation pressure in LBV atmospheres

1989 ◽  
Vol 113 ◽  
pp. 195-204
Author(s):  
I. Appenzeller
Keyword(s):  
Mass Loss ◽  
Radiation Pressure ◽  
Large Amplitude ◽  
Pressure Effects ◽  
Radiative Acceleration

AbstractAs LBVs have luminosities close to their Eddington limits, their structure is profoundly influenced by radiation pressure. Radiation pressure effects probably cause the highly extended atmospheres and the extreme mass loss observed during the maximum states of the S Dor variables. An opacity-related instability of the radiative acceleration combined with a delayed thermal readjustement of the sub-atmospheric layers possibly explains the large-amplitude radius variations of these objects.

scholarly journals A STUDY OF THE ROLE OF Lyβ FLUORESCENCE ON O I LINE STRENGTHS IN Be STARS

2012 ◽  
Vol 753 (1) ◽  
pp. 13 ◽  
Author(s):  
Blesson Mathew ◽  
D. P. K. Banerjee ◽  
A. Subramaniam ◽  
N. M. Ashok
Keyword(s):  
Be Stars ◽  
Line Strengths

scholarly journals Non-radially Pulsating Hot Stars: Non-radial Pulsations and Be Phenomenon

1999 ◽  
Vol 169 ◽  
pp. 329-336
Author(s):  
Yoji Osaki
Keyword(s):  
Mass Loss ◽  
Relaxation Oscillation ◽  
Stellar Atmosphere ◽  
Circumstellar Disk ◽  
Circumstellar Envelope ◽  
Be Stars ◽  
Hot Stars ◽  
Disk Model ◽  
Rotating Star

AbstractWe discuss a possible role of non-radial oscillations as a cause of mass-loss in hot stars. In particular, we propose a working model for the episodic mass-loss in Be stars. In this model, equatorial mass loss is thought to be driven by wave-breaking phenomenon of large-amplitude non-radial waves and a circumstellar disk could thus be formed around the equatorial plane of a rapidly rotating star. A kind of relaxation-oscillation cycle could be established between the Be phase and non-Be phase, in which an interplay between non-radial oscillations in stellar atmosphere and the circumstellar disk is essential. We also discuss a viscous decretion-disk model for the circumstellar envelope around Be stars.

scholarly journals Diffusion and Metal Abundances in Hot White Dwarfs Gerard Vauclair

1989 ◽  
Vol 114 ◽  
pp. 176-187 ◽  
Author(s):  
Gérard Vauclair
Keyword(s):  
Time Scales ◽  
White Dwarf ◽  
White Dwarfs ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
Metal Abundances ◽  
Cool White Dwarfs ◽  
First Time ◽  
Radiative Acceleration

While the efficiency of gravitational settling to produce chemically pure atmospheres in white dwarf stars was outlined for the first time 30 years ago (Schatzman 1958), the competing role of the radiation flux in the hot white dwarfs was considered only 10 years ago (Fontaine and Michaud 1979; Vauclair, Vauclair and Greenstein 1979). At that time, there was more motivation to understand how metals could reappear in the long lived cool non DA white dwarfs, where diffusion time scales are shorter by orders of magnitude than evolutionary time scales. Various processes were invoked to help restore some metal content in the white dwarf atmospheres: convection mixing and dredge up, accretion of interstellar matter. In cool white dwarfs, the radiative acceleration is negligeable in the diffusion process; this is not the case at the hot end of the sequence where radiation may balance gravity. The short lived hot white dwarfs just started to become exciting with the contemporary discoveries that i) some show metallic lines in their spectra, both hydrogen rich and hydrogen poor; ii) some of these are pulsating. In the following years, the number of hot white dwarfs revealing trace abundance of metals has increased, mainly owing to IUE observations.

scholarly journals Making a Be star: the role of rotation and pulsations

2013 ◽  
Vol 9 (S301) ◽  
pp. 465-466
Author(s):  
Coralie Neiner ◽  
Stéphane Mathis
Keyword(s):  
Angular Momentum ◽  
Critical Value ◽  
Circumstellar Disk ◽  
Be Stars ◽  
Stochastic Excitation ◽  
Stellar Rotation ◽  
Rapid Rotation ◽  
Be Star

AbstractThe Be phenomenon, i.e. the ejection of matter from Be stars into a circumstellar disk, has been a long lasting mystery. In the last few years, the CoRoT satellite brought clear evidence that Be outbursts are directly correlated to pulsations and rapid rotation. In particular the stochastic excitation of gravito-inertial modes, such as those detected by CoRoT in the hot Be star HD 51452, is enhanced thanks to rapid rotation. These waves increase the transport of angular momentum and help to bring the already rapid stellar rotation to its critical value at the surface, allowing the star to eject material. Below we summarize the recent observational and theoretical findings and describe the new picture of the Be phenomenon which arose from these results.

scholarly journals Binary Be Stars and Be Binaries

1992 ◽  
Vol 151 ◽  
pp. 147-156
Author(s):  
Dietrich Baade
Keyword(s):  
Angular Momentum ◽  
Momentum Transfer ◽  
Mass Exchange ◽  
White Dwarf ◽  
Be Stars ◽  
Star Model ◽  
Rapid Rotation ◽  
Sky Survey ◽  
Be Star

Two hypotheses have been put forward for the rôle of binarity in Be stars: (1) All Be stars are interacting binaries. (2) Roughly one-half of the observed Be stars are post-mass exchange binaries with compact companions. Contrary to (1), (2) does not attempt to explain also the existence of disks in Be stars. After the spin-up by mass and angular momentum transfer, the B star somehow has to succeed to form and maintain the disk. Since rapid rotation is only necessary but not sufficient for this transformation, the effect of duplicity would merely be to give more stars the opportunity to become a Be star. Model (1) is not nearly realistic as is also underlined by a new spectroscopic survey for cool companions. The verification of (2) on the basis of the ROSAT All-Sky Survey has just begun; but a serious deficiency of white dwarf companions is already apparent. Binarity currently provides no extra clue on the origin of the Be phenomenon.

scholarly journals A Survey of Mass Loss from Be and Shell Stars Using Ultraviolet Data from Copernicus

1976 ◽  
Vol 70 ◽  
pp. 179-189 ◽  
Author(s):  
J. M. Marlborough ◽  
Theodore P. Snow
Keyword(s):  
Mass Loss ◽  
Direct Evidence ◽  
Rotational Velocity ◽  
Stellar Winds ◽  
Be Stars ◽  
Dwarf Stars ◽  
Be Star ◽  
Effects Of Rotation ◽  
First Time

Ultraviolet spectra of intermediate resolution have been obtained with Copernicus of twelve objects classified as Be or shell stars, and an additional 19 dwarfs of spectral classes B0-B4. Some of these spectra show marked asymmetries in certain resonance lines, especially the Si iv doublet at λ 1400 Å, indicating the presence of outflowing material with maximum velocities of nearly 1000 km s−1. Direct evidence for mass loss at these velocities is seen for the first time in dwarf stars as late as B1.5. Later than B0.5, the only survey objects showing this phenomenon are Be stars. Among the stars considered there is a correlation between the presence of mass-loss effects and projected rotational velocity, suggesting that the UV flux from B1-B3 dwarfs is sufficient to drive high-velocity stellar winds only if rotation reduces the effective gravity near the equator. The role of mass-loss in producing the Be star phenomenon and the effects of rotation on mass loss are discussed.

scholarly journals Rotation and Mass Ejection: the Launching of Be-Star Disks

2004 ◽  
Vol 215 ◽  
pp. 515-524 ◽  
Author(s):  
Stanley P. Owocki
Keyword(s):  
Binary Systems ◽  
Line Emission ◽  
Circumstellar Disk ◽  
Balmer Line ◽  
Be Stars ◽  
Wide Binary ◽  
Orbital Mass ◽  
Be Star ◽  
Mass Ejection

The characteristic signature of Be Stars is the Balmer line emission understood to arise in a circumstellar disk. Unlike the accretion disks of protostars or mass-exchange binary systems, the evolved and generally single or wide-binary status of Be Stars seems to require that its disk must form from mass ejection (a.k.a. decretion) from the star itself. In this paper, I use analogies with launching orbital satellites to discuss two candidate processes (radiation, pulsation) for driving such orbital mass ejection, with particular emphasis on the role of the rapid, possibly near-critical, rotation of Be Stars in facilitating the formation of their signature disks.

scholarly journals Magnetism, rotation and accretion in Herbig Ae-Be stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 43-50 ◽  
Author(s):  
E. Alecian ◽  
G.A. Wade ◽  
C. Catala ◽  
C. Folsom ◽  
J. Grunhut ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Be Stars ◽  
Origin And Evolution ◽  
Intermediate Mass Stars ◽  
New Information ◽  
Late Formative ◽  
Stellar Masses ◽  
Late Stages

AbstractStudies of stellar magnetism at the pre-main sequence phase can provide important new insights into the detailed physics of the late stages of star formation, and into the observed properties of main sequence stars. This is especially true at intermediate stellar masses, where magnetic fields are strong and globally organised, and therefore most amenable to direct study. This talk reviews recent high-precision ESPaDOnS observations of pre-main sequence Herbig Ae-Be stars, which are yielding qualitatively new information about intermediate-mass stars: the origin and evolution of their magnetic fields, the role of magnetic fields in generating their spectroscopic activity and in mediating accretion in their late formative stages, and the factors influencing their rotational angular momentum.

Sign in / Sign up

Export Citation Format

Share Document