scholarly journals The Spheroidal/Ellipsoidal, Variable Mass-Loss, Decelerated Be Star Model (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 384-410 ◽  
Author(s):  
V. Doazan
Keyword(s):  
Variable Mass ◽  
Thermodynamic Characteristics ◽  
Be Stars ◽  
Star Model ◽  
B Stars ◽  
Proposed Model ◽  
Mass Outflow ◽  
Be Star ◽  
Model Review ◽  
The One

The proposed model is empirical; it is based on analysis of the available data on Be stars obtained in all the observable spectral regions, and it is required to be thermodynamically self-consistent. Rather than trying to answer the question: “What is the origin of the Be-phenomenon?” We ask: First. “What phenomena characterize empirically Be stars?” Second, “What thermodynamic characteristics are implied by the existence of such phenomena?” Third. “What inferences may be made an the atmospheric structure of a Be star from these empirical and thermodynamical characteristics?” The observed phenomena, their thermodynamical implications and the resulting model have each two aspects. On the one hand, the observational evidence for a nonradiatively heated, expanding chromosphere-corona implies the existence of both a nonradiative energy flux and a mass outflow from the photosphere. This first aspect is common to both Be and normal B stars, at least for the earliest subtypes.

scholarly journals Interstellar Absorption of Some Be Stars

1987 ◽  
Vol 92 ◽  
pp. 214-216 ◽  
Author(s):  
D. Briot ◽  
J. Zorec
Keyword(s):  
Circumstellar Matter ◽  
Be Stars ◽  
Interstellar Absorption ◽  
B Stars ◽  
Be Star

It is well known that the intrinsic colors of Be stars are not the same as those of “normal” B stars and they are often redder. So interstellar absorption of Be stars determined from photometric indices may be overestimated. In order to avoid this, a method often used to determine the interstellar absorption of Be stars is based on the ultraviolet interstellar absorption bump at 2200 Å (Dorschner 1975; Nandy et al. 1975, 1976). However some peculiar Be stars exist whose circumstellar matter contributes to the 2200 Å bump (Savage et al. 1978). The aim of this work is to test the deredenning method from the 2200 Å bump for “classical” Be stars, in determining the interstellar absorption in the region of the Be star, using the surrounding normal stars.

scholarly journals Infrared properties of active OB stars in the Magellanic Clouds from the Spitzer SAGE survey

2010 ◽  
Vol 6 (S272) ◽  
pp. 254-259
Author(s):  
Alceste Z. Bonanos ◽  
Danny J. Lennon ◽  
Derck L. Massa ◽  
Marta Sewilo ◽  
Fabian Köhlinger ◽  
...  
Keyword(s):  
Magellanic Clouds ◽  
Spectral Energy ◽  
Be Stars ◽  
Energy Distributions ◽  
Photometric Variability ◽  
B Stars ◽  
Ob Stars ◽  
Luminous Blue Variables ◽  
Red Supergiants ◽  
Be Star

AbstractWe present a study of the infrared properties of 4922 spectroscopically confirmed massive stars in the Large and Small Magellanic Clouds, focusing on the active OB star population. Besides OB stars, our sample includes yellow and red supergiants, Wolf-Rayet stars, Luminous Blue Variables (LBVs) and supergiant B[e] stars. We detect a distinct Be star sequence, displaced to the red, and find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We also find photometric variability among the active OB population and evidence for transitions of Be stars to B stars and vice versa. We furthermore confirm the presence of dust around all the supergiant B[e] stars in our sample, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs.

scholarly journals Nonradial pulsations in the open cluster NGC 3766

2009 ◽  
Vol 5 (S266) ◽  
pp. 518-521
Author(s):  
Rachael M. Roettenbacher ◽  
Ernest C. Amouzou ◽  
M. Virginia McSwain
Keyword(s):  
Signal To Noise Ratio ◽  
Large Fraction ◽  
Open Cluster ◽  
Spectroscopic Studies ◽  
High Resolution Spectroscopy ◽  
High Signal ◽  
Be Stars ◽  
B Stars ◽  
Be Star ◽  
Large Telescopes

AbstractNonradial pulsations (NRPs) are a proposed mechanism for the formation of decretion disks around Be stars. They are important tools to study the internal structure of stars. NGC 3766 has an unusually large fraction of transient Be stars, so it is an excellent location to study the formation mechanism of Be-star disks. High-resolution spectroscopy can reveal line-profile variations from NRPs, allowing measurements of both the degree, l, and azimuthal order, m. However, spectroscopic studies require large amounts of time with large telescopes to achieve the necessary high signal-to-noise ratio and time-domain coverage. On the other hand, multicolor photometry can be performed more easily with small telescopes to measure l only. Here, we present representative light curves of Be stars and nonemitting B stars in NGC 3766 from the CTIO 0.9m telescope in an effort to study NRPs in this cluster.

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 On the Percentage of Be Stars in Galactic Open Clusters

1987 ◽  
Vol 92 ◽  
pp. 503-504
Author(s):  
A. Reitermann ◽  
J. Krautter ◽  
B. Wolf ◽  
B. Bashek
Keyword(s):  
Spectroscopic Study ◽  
Open Clusters ◽  
Evolutionary Status ◽  
Be Stars ◽  
Chemical Abundance ◽  
B Stars ◽  
Knowing That ◽  
Be Star ◽  
High Fraction ◽  
Young Clusters

Knowing that especially young clusters can contain a considerable high fraction of Be stars (Mermilliod 1982, Feast 1972) we made a spectroscopic study of Hα on the ratio of B/Be stars. The aim was to select normal B stars for chemical abundance analyses.It is well known that a promising way to investigate the evolutionary status of Be stars is to study their frequency and positions in the H-R diagram of open clusters. However, these studies have not yet provided satisfactory results (cf. e.g. Slettebak 1985); observations concerning the B/Be star ratio are badly needed. Therefore we present our observations although they are only a by-product from a different program.

scholarly journals Long-Term V/R Variations of be Stars Due to Global One-Armed Oscillations of Equatorial Disks

1993 ◽  
Vol 134 ◽  
pp. 369-370
Author(s):  
Atsuo T. Okazaki
Keyword(s):  
Nonlinear Oscillations ◽  
Balmer Line ◽  
Density Gradients ◽  
Be Stars ◽  
Line Profiles ◽  
Be Star ◽  
On Line ◽  
The One ◽  
Long Term Variations

AbstractWe study the long-term variations of Balmer line profiles due to global one-armed oscillations in Be-star disks. In order to examine the qualitative effects of oscillations on line profiles, we assume that the eigenfunctions of one-armed nonlinear oscillations are similar to those of linear oscillations. Computing the line profiles for various values of disk parameters, we find that in small disks or in disks with steep density gradients the one-armed fundamental modes cause remarkable variabilities similar to the observed V/R variations.

scholarly journals Introductory Address

1976 ◽  
Vol 70 ◽  
pp. 1-10
Author(s):  
Miroslav Plavec
Keyword(s):  
Binary Star ◽  
Early History ◽  
Be Stars ◽  
Star Model ◽  
Basic Model ◽  
History Of ◽  
Be Star

The early history of the studies on Be stars is reviewed. The importance of keeping in mind a basic model of a Be star is emphasized, and the binary star model is suggested as one serious possibility at least for some Be stars.

scholarly journals Destruction of Be star disk by large scale magnetic fields

2016 ◽  
Vol 12 (S329) ◽  
pp. 453-453
Author(s):  
Asif ud-Doula ◽  
Stanley Owocki ◽  
Nathaniel (Dylan) Kee ◽  
Michael Vanyo
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Circumstellar Disks ◽  
Be Stars ◽  
Rotating Stars ◽  
Apparent Lack ◽  
B Stars ◽  
Large Scale Magnetic Field ◽  
Be Star ◽  
Rapidly Rotating Stars

AbstractClassical Be stars are rapidly rotating stars with circumstellar disks that come and go on time scale of years. Recent observational data strongly suggests that these stars lack the 10% incidence of global magnetic fields observed in other main-sequence B stars. Such an apparent lack of magnetic fields may indicate that Be disks are fundamentally incompatible with a significant large scale magnetic field. In this work, using numerical magnetohydrodynamics (MHD) simulations, we show that a dipole field of only 100G can lead to the quick disruption of a Be disk. Such a limit is in line with the observational upper limits for these objects.

scholarly journals A stripped-companion origin for Be stars: clues from the putative black holes HR 6819 and LB-1

2021 ◽  
Vol 502 (3) ◽  
pp. 3436-3455
Author(s):  
Kareem El-Badry ◽  
Eliot Quataert
Keyword(s):  
Evolutionary History ◽  
Orbital Motion ◽  
Be Stars ◽  
Star Model ◽  
Intermediate Mass ◽  
Normal Star ◽  
Composite Spectra ◽  
Evolutionary Phase ◽  
Be Star ◽  
Helium Star

ABSTRACT HR 6819 is a bright (V = 5.36), blue star recently proposed to be a triple containing a detached black hole (BH). We show that the system is a binary and does not contain a BH. Using spectral decomposition, we disentangle the observed composite spectra into two components: a rapidly rotating Be star and a slowly rotating B star with low surface gravity (log g ≈ 2.75). Both stars show periodic radial velocity (RV) variability, but the RV semi-amplitude of the B star’s orbit is $K_{\rm B}= (62.7 \pm 1)\, \rm km\, s^{-1}$, while that of the Be star is only $K_{\rm Be} = (4.5\pm 2)\, \rm km\, s^{-1}$. This implies that the B star is less massive by at least a factor of 10. The surface abundances of the B star bear imprints of CNO burning. We argue that the B star is a bloated, recently stripped helium star with mass ${\approx}0.5\, \mathrm{ M}_{\odot }$ that is currently contracting to become a hot subdwarf. The orbital motion of the Be star obviates the need for a BH to explain the B star’s motion. A stripped-star model reproduces the observed luminosity of the system, while a normal star with the B star’s temperature and gravity would be more than 10 times too luminous. HR 6819 and the binary LB-1 probably formed through similar channels. We use MESA (Modules for Experiments in Stellar Astrophysics) models to investigate their evolutionary history, finding that they likely formed from intermediate-mass ($3\!-\!7\, \mathrm{ M}_{\odot }$) primaries stripped by slightly lower-mass secondaries and are progenitors to Be + sdOB binaries such as ϕ Persei. The lifetime of their current evolutionary phase is on average 2 × 105 yr, of the order of half a per cent of the total lifetime of the Be phase. This implies that many Be stars have hot subdwarf and white dwarf companions, and that a substantial fraction ($20\!-\!100{{\ \rm per\ cent}}$) of field Be stars form through accretion of material from a binary companion.

A Relativistic Newtonian Mechanics Predicts with Precision the Results of Recent Neutrino-Velocity Experiments

2014 ◽  
Vol 6 (1) ◽  
pp. 1032-1035 ◽  
Author(s):  
Ramzi Suleiman
Keyword(s):  
Null Hypothesis ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Newtonian Mechanics ◽  
Speed Of Light ◽  
Symmetry Principle ◽  
Proposed Model ◽  
Significant Difference ◽  
The One ◽  
Complete Collapse

The research on quasi-luminal neutrinos has sparked several experimental studies for testing the "speed of light limit" hypothesis. Until today, the overall evidence favors the "null" hypothesis, stating that there is no significant difference between the observed velocities of light and neutrinos. Despite numerous theoretical models proposed to explain the neutrinos behavior, no attempt has been undertaken to predict the experimentally produced results. This paper presents a simple novel extension of Newton's mechanics to the domain of relativistic velocities. For a typical neutrino-velocity experiment, the proposed model is utilized to derive a general expression for . Comparison of the model's prediction with results of six neutrino-velocity experiments, conducted by five collaborations, reveals that the model predicts all the reported results with striking accuracy. Because in the proposed model, the direction of the neutrino flight matters, the model's impressive success in accounting for all the tested data, indicates a complete collapse of the Lorentz symmetry principle in situation involving quasi-luminal particles, moving in two opposite directions. This conclusion is support by previous findings, showing that an identical Sagnac effect to the one documented for radial motion, occurs also in linear motion.

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