scholarly journals Non-radial pulsations in the CoRoT Be Star 102761769

2010 ◽  
Vol 6 (S272) ◽  
pp. 507-508
Author(s):  
Eduardo Janot Pacheco ◽  
Laerte B.P. de Andrade ◽  
Marcelo Emilio ◽  
Juan Carlos Suárez ◽  
Andressa Jendreieck
Keyword(s):  
Critical Velocity ◽  
Be Stars ◽  
Stellar Rotation ◽  
Alternative Scenario ◽  
Be Star ◽  
Radial Pulsations ◽  
Nonradial Oscillations

AbstractWe investigate non-radial pulsations of the CoRoT IR1 Be Star 102761769, with a projected stellar rotation estimated to be 120±15 km/s. If the star is a typical galactic Be star it rotates near the critical velocity. We propose an alternative scenario, where the star could be seen nearly equator-on rotating at a relatively moderate velocity say, ≈ 120 km/s and therefore the nonradial oscillations could be modeled. In order to identify the pulsation modes of the observed frequencies, we computed a set of models representative of CoRoT 102761769 by means of the adiabatic pulsation package FILOU. Results indicate that the two frequencies are compatible with a high-g mode as predicted by pulsation models of Be stars.

scholarly journals Radiation driven winds with rotation: the oblate finite disc correction factor

2010 ◽  
Vol 6 (S272) ◽  
pp. 83-84
Author(s):  
Ignacio Araya ◽  
Michel Curé ◽  
Anahí Granada ◽  
Lydia S. Cidale
Keyword(s):  
Critical Velocity ◽  
Correction Factor ◽  
Rotational Velocity ◽  
Momentum Equation ◽  
Be Stars ◽  
Stellar Rotation ◽  
Polar Wind ◽  
Be Star ◽  
Remarkable Result ◽  
Standing Problem

AbstractWe have incorporated the oblate distortion of the shape of the star due to the stellar rotation, which modifies the finite disk correction factor (fD) in the m-CAK hydrodynamical model. We implement a simplified version for the fD allowing us to solve numerically the non–linear m-CAK momentum equation. We solve this model for a classical Be star in the polar and equatorial directions. The star's oblateness modifies the polar wind, which is now much faster than the spherical one, mainly because the wind receives radiation from a larger (than the spherical) stellar surface. In the equatorial direction we obtain slow solutions, which are even slower and denser than the spherical ones. For the case when the stellar rotational velocity is about the critical velocity, the most remarkable result of our calculations is that the density contrast between the equatorial density and the polar one, is about 100. This result could explain a long-standing problem on 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 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 Rotationally-Enhanced Stellar Winds (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 316-338
Author(s):  
J. M. Marlborough
Keyword(s):  
Mass Transfer ◽  
Stellar Wind ◽  
Review Paper ◽  
Current Status ◽  
Stellar Winds ◽  
Be Stars ◽  
Stellar Rotation ◽  
Circumstellar Envelopes ◽  
Wind Model ◽  
Be Star

The rotationally-enhanced stellar wind model for Be stars represents one attempt to understand many of the phenomena related to Be stars in terms of a stellar wind distorted and perhaps also enhanced by rapid stellar rotation. This review will concentrate exclusively on this particular approach; the current status of other attempts to model the circumstellar envelopes (CE) of Be stars are described in other reviews in this volume. It is assumed that Be stars are single stars; if a member of a multiple system, the separation of all components from the Be star is assumed to be sufficiently large that interactions due to mass transfer from any companion to the Be star are negligible.

Dynamics of Self-Accreting Disks in Be Stars

1997 ◽  
Vol 163 ◽  
pp. 494-497 ◽  
Author(s):  
P. Kroll ◽  
R.W. Hanuschik
Keyword(s):  
Angular Momentum ◽  
Critical Velocity ◽  
Stellar Surface ◽  
Ejection Velocity ◽  
Be Stars ◽  
Stellar Matter ◽  
High Angular Momentum ◽  
Viscous Forces ◽  
Disk Material ◽  
Be Star

AbstractBe star disks are formed by ejection of stellar matter from the surface of a B star rotating at almost critical velocity. In SPH simulations we find that most of the ejected particles fall back on the stellar surface but those with sufficient angular momentum are able to feed a disk-like structure. Owing to viscous interaction some particles are lifted to larger radii where they carry high angular momentum. Viscous forces also cause a thinning of the initially geometrically thick disk and the final accretion of most of the disk material. Different simulations show how the formation and the extension of the decretion disk depend on the ejection velocity, the viscous parameter α and on how long the source is active. After the outburst the disk thins out more and more, over a timescale much longer than the outburst time.The simulations are compared to Hα observations of the Be star µ Cen.

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 Probing Be star disks: new insights from Hα spectroscopy and detailed numerical models

2010 ◽  
Vol 6 (S272) ◽  
pp. 398-399 ◽  
Author(s):  
Carol E. Jones ◽  
Christopher Tycner ◽  
Jessie Silaj ◽  
Ashly Smith ◽  
T. A. Aaron Sigut
Keyword(s):  
High Resolution ◽  
Numerical Models ◽  
Analytical Tool ◽  
High Resolution Spectroscopy ◽  
Be Stars ◽  
Line Shapes ◽  
Physical Conditions ◽  
Temperature Distributions ◽  
Inclination Angles ◽  
Be Star

AbstractHα high resolution spectroscopy combined with detailed numerical models is used to probe the physical conditions, such as density, temperature, and velocity of Be star disks. Models have been constructed for Be stars over a range in spectral types and inclination angles. We find that a variety of line shapes can be obtained by keeping the inclination fixed and changing density alone. This is due to the fact that our models account for disk temperature distributions self-consistently from the requirement of radiative equilibrium. A new analytical tool, called the variability ratio, was developed to identify emission-line stars at particular stages of variability. It is used in this work to quantify changes in the Hα equivalent widths for our observed spectra.

scholarly journals Apparent Variation of v sin i and Rotational Modulation in Be Stars

2004 ◽  
Vol 215 ◽  
pp. 93-94
Author(s):  
C. Neiner ◽  
S. Jankov ◽  
M. Floquet ◽  
A. M. Hubert
Keyword(s):  
Fourier Transform ◽  
Magnetic Dipole ◽  
Be Stars ◽  
Line Profiles ◽  
Transform Method ◽  
Rotational Modulation ◽  
Be Star ◽  
Apparent Variation ◽  
The Fourier Transform ◽  
First Time

v sin i was determined by applying the Fourier transform method to the line profiles of two classical Be Stars. A variation is observed in the apparent v sin i which corresponds to the main frequencies associated to nrp modes. Rotational modulation is observed in wind sensitive UV lines of the Be star ω Ori and is associated with an oblique magnetic dipole which is discovered for the first time in a classical Be star.

scholarly journals Correlations Between BCD Parameters of the Continuous Spectrum and the Balmer Decrement of Be Stars

1982 ◽  
Vol 98 ◽  
pp. 53-56 ◽  
Author(s):  
L. Divan ◽  
J. Zorec ◽  
D. Briot
Keyword(s):  
Continuous Spectrum ◽  
Interstellar Extinction ◽  
Be Stars ◽  
Be Star ◽  
Balmer Decrement

One of the greatest difficulties in interpreting the continuous spectrum of Be stars is to separate the effects of interstellar reddening from the effects due to the presence of the envelope. This difficulty has been avoided in the two types of correlations considered here. In the first one, parameters not affected by interstellar reddening are used (the Balmer jump and the Balmer decrement). In the second one, the parameters used can be affected by the interstellar extinction but comparisons are made only between values which correspond to the same (but variable) Be star, at different epochs, with different amounts of emission.

scholarly journals Polarimetry and Physics of Be Star Envelopes (Review paper)

1982 ◽  
Vol 98 ◽  
pp. 77-93 ◽  
Author(s):  
George V. Coyne ◽  
Ian S. McLean
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Theoretical Models ◽  
Geometrical Parameters ◽  
Be Stars ◽  
Intermediate Band ◽  
Wide Range ◽  
Recent Developments ◽  
Be Star ◽  
Polarization Studies

A review of the most recent developments in polarization studies of Be stars is presented. New polarization techniques for high-resolution spectropolarimetry and for near infrared polarimetry are described and a wide range of new observations are discussed. These include broadband, intermediate-band and multichannel observations of the continuum polarization of Be stars in the wavelenght interval 0.3–2.2 microns, high resolution (0.5 Å) line profile polarimetry of a few stars and surveys of many stars for the purposes of statistical analyses. The physical significance of the observational material is discussed in the light of recent theoretical models. Emphasis is placed on the physical and geometrical parameters of Be star envelopes which polarimetry helps to determine.

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