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 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 Where do Be stars stand in the picture of rotational mixing?

2010 ◽  
Vol 6 (S272) ◽  
pp. 85-86
Author(s):  
Paul R. Dunstall ◽  
Ines Brott ◽  
Philip L. Dufton ◽  
Chris J. Evans
Keyword(s):  
Critical Velocity ◽  
Rotational Velocity ◽  
Magellanic Clouds ◽  
Evolutionary Status ◽  
Evolutionary Models ◽  
Be Stars ◽  
Atmospheric Parameters ◽  
B Stars ◽  
The Absolute ◽  
Fast Rotating

AbstractAtmospheric parameters and photospheric abundances have been estimated for 60 Be-type stars located in 4 fields over the Magellanic Clouds. Particular attention has been given to the absolute nitrogen abundances to test theories of rotational mixing, an important factor in the evolutionary status of B-type stars, Hunter et al. (2008). The analysis used the non-LTE atmospheric code TLUSTY and required the implementation of a procedure to compensate for possible contamination due to the presence of a circumstellar disc. Through comparison with evolutionary models of fast rotating B-type stars and projected rotational velocity distributions our results support the theory that Be-type stars are typically faster rotators than B stars, but the measured nitrogen enhancements appear to be significantly less than expected for Be stars rotating with velocities greater than 70% of their critical velocity

scholarly journals Problems of Gaseous Motion Around Stars

1973 ◽  
Vol 51 ◽  
pp. 22-47
Author(s):  
Su-Shu Huang
Keyword(s):  
Gravitational Field ◽  
Binary Systems ◽  
Rotational Velocity ◽  
Point Of View ◽  
Temperature Sensitive ◽  
Be Stars ◽  
Jet Streams ◽  
Circumstellar Material ◽  
Be Star ◽  
Gaseous Envelopes

A distinction is drawn between radial and tangential modes of ejection from stars, and the possible flow patterns are described. They are: expanding streams, falling streams, jet streams, circulatory streams, and gaseous envelopes. Motion around Be stars is discussed at some length, as a preliminary to studying more complicated flow in binary systems. The rotational velocity of the Be star is insufficient to form the ring. It appears likely that radial instability is temperature sensitive. Rings and disks in binary systems are discussed from the point of view of periodic orbits for particles within the gravitational field of such a system. The formation of these rings is discussed. The expected relation between rotational velocity of the ring and the orbital period is discussed. The relation of circumstellar streams to period changes is mentioned. Finally, the influence of magnetic fields on the circumstellar material and the system is discussed.

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 Results from a recent stellar rotation census of B stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 89-90
Author(s):  
Wenjin Huang ◽  
Douglas R. Gies ◽  
M. Virginia McSwain
Keyword(s):  
Effective Temperature ◽  
Rotation Rate ◽  
Rotation Speed ◽  
Rotational Velocity ◽  
Rotation Velocity ◽  
Be Stars ◽  
Stellar Rotation ◽  
B Stars ◽  
Critical Rotation ◽  
Critical Rotation Speed

AbstractIn an analysis of the rotational properties of more than 1100 B stars (~660 cluster and ~500 field B stars), we determine the projected rotational velocity (V sin i), effective temperature, gravity, mass, and critical rotation speed for each star. The new data provide us a solid observational base to explore many hot topics in this area: Why do field B stars rotate slower than cluster B stars? How fast do B stars rotate when they are just born? How fast can B stars rotate before they become Be stars? How does the rotation rate of B stars change with time? Does the evolutionary change in rotation velocity lead to the Be phenomenon? Here we report the results of our efforts in searching for answers to these questions based on the latest B star census.

scholarly journals HR 4074: an Emission-Free NRP Twin of the Be Star 28 CMa

2002 ◽  
Vol 185 ◽  
pp. 248-249
Author(s):  
S. Štefl ◽  
Th. Rivinius ◽  
D. Baade
Keyword(s):  
Time Series ◽  
Line Profile ◽  
Rotational Velocity ◽  
Be Stars ◽  
Narrow Component ◽  
Rotational Modulation ◽  
Line Core ◽  
Emission Activity ◽  
History Of ◽  
Be Star

In spite of considerable progress in the investigation of rapid line-profile variations (lpv) of Be stars, at least two models still compete in the literature: the rotational modulation, assuming mostly corotating circumstellar structures (Balona, 2000), and nonradial pulsations (Maintz et al. and Rivinius et al., these proceedings). Attempts to explain the lpv of Be stars were often connected with the proto-typical star 28 (ω) CMa (HR 2749 = HD 56139, B2IV-Ve, v sin i = 80 km/s). Štefl et al. (1998) described variability in three line-profile components: in the narrow component of the line core, in the line core itself and in the wings. The Balmer emission of 28 CMa is variable and has always been observed to be at least moderate, mostly strong.HR 4074 (HD 89890, B3 III, v sin i = 70 km/s) has a different history of its emission activity. From a single spectrogram taken in 1893, Pickering (1898) reported an emission in Hβ. Subsequent observations never confirmed this. If it was not mis-identified by Pickering, HR 4074 would be in the probably longest B-star phase known of any Be star. HR 4074 is very probably not an SPB star - the spectral type is too early, the rotational velocity too high and light variations too low for this classification. Baade (1984) detected rapid lpv with a period P ≈ 2.25 d. Our time series analysis of radial velocity (RV) variations, measured as line modes, and that of full profiles give P = (2.3179 ± 0.0008) d.

scholarly journals Interferometric survey of Be stars with the CHARA array

2010 ◽  
Vol 6 (S272) ◽  
pp. 634-635 ◽  
Author(s):  
Yamina N. Touhami ◽  
Douglas R. Gies ◽  
Gail H. Schaefer ◽  
Noel D. Richardson ◽  
Stephen J. Williams ◽  
...  
Keyword(s):  
Rotational Velocity ◽  
Circumstellar Disks ◽  
Geometrical Parameters ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Disk Model ◽  
Spatially Resolved ◽  
Near Ir ◽  
Be Star ◽  
Chara Array

AbstractWe present the first spatially resolved observations of circumstellar envelopes of 25 bright northern Be stars. The survey was performed with the CHARA Array interferometer in the K-band at intermediate and long baselines. The interferometric visibilities are well fitted by a viscous disk model where the gas density steeply decreases with the radius. Physical and geometrical parameters such as the density profile, the inclination, and the position angles of the circumstellar disks are determined. We find that the density radial exponent ranges between n ≈ 2.4 − 3.2, which is consistent with previous IRAS measurements. We have also obtained simultaneous optical and near-IR spectrophotometric measurements, and found that the model reproduces well the observed disk IR-continuum excess emission. By combining the projected rotational velocity of the Be star with the disk inclination derived from interferometry, we give estimates of the equatorial rotational velocities of these Be stars.

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 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.

scholarly journals The Flux Distributions of Be Stars in the Far-UV

1987 ◽  
Vol 92 ◽  
pp. 272-273
Author(s):  
Roberto Stalio ◽  
Ronald S. Polidan ◽  
Geraldine J. Peters
Keyword(s):  
Critical Velocity ◽  
Flux Distribution ◽  
Rotational Velocity ◽  
Spectroscopic Studies ◽  
Be Stars ◽  
Parallel Study ◽  
Model Calculations ◽  
Star Models ◽  
Rotating Star ◽  
Initial Results

AbstractThe initial results of a program to investigate the far-UV (500-1700 A) spectra of Be stars using the Voyager ultraviolet spectrometers axe presented. Observations of eleven Be stars, with spectral types from B0 through B7, obtained between March 1979 and July 1984 are discussed. The Voyager resolution (∼15 A) allows only limited spectroscopic studies; shortward of 1150 A C III λ977 and LyJβ λ1025 are the most prominent spectral features. Two stars, γ Cas and 59 Cyg, showed enhanced C III λ977 absorption. The flux distributions of the Be stars were intercompared with those of reference stars with low projected rotational velocities and, in a parallel study, to predictions from rotating star models. The model calculations suggest that the observable effects of a high rotational velocity (V≳ 0.9 of critical velocity) on the flux distribution are small except in the FUV (λ < 1150A). The Voyager flux distributions were found to be indistinguishable from those of the low v sin i reference stars. No evidence was found for critical rotation in Be stars. All observations were consistent with Be stars rotating at less than 0.85 of critical velocity.

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