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.

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 The evolutionary history of BE/X-ray binaries

1984 ◽  
Vol 105 ◽  
pp. 399-402 ◽  
Author(s):  
G.M.H.J. Habets
Keyword(s):  
Mass Transfer ◽  
Evolutionary History ◽  
Transfer Phase ◽  
Intermediate Mass ◽  
X Ray ◽  
History Of ◽  
Helium Star ◽  
X Ray Binaries

A 2.5 M⊙helium star remnant of a Case B mass transfer is evolved to off-centre neon ignition and a second mass transfer phase, Case BB, is explored. The model for the formation of Be/X-ray binaries by mass-transfer dominated evolution in an intermediate mass binary is confirmed.

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 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 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.

scholarly journals Multiple dust shells around Herbig Ae/Be stars

1987 ◽  
Vol 122 ◽  
pp. 99-100
Author(s):  
P.S. Thé ◽  
D. N. Dawanas
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Spectral Energy Distribution ◽  
Far Infrared ◽  
Central Star ◽  
Spectral Energy ◽  
Be Stars ◽  
Intermediate Mass ◽  
Dust Shells ◽  
Average Size

Intermediate mass (2 < M/M⊙ < 9) pre-main sequence objects, also named Herbig Ae/Be stars, are known to have excess radiation in the near-infrared. From IRAS o bservations it turns out without doubt (quality 3, high S/N radio), that these objects are very strong far-infrared emitters at 12, 25, 60 and often also at 100 μm. The spectral energy distribution, depicted in Fig. 1 for intermediate mass pre-main sequence stars, show clearly this large excess. From the difference curves it is apparent that this excess radiation is most probably caused by several dust shells. Using very simplified methods it is possible to derive the average temperature of the dust shells (see Thé, Wesselius, Tjin A Djie and Steenman, 1986). If the chemical composition of the mixture of the dust grains and their average size are assumed it is also possible to estimate other characteristics like the distance from the central star and the mass of the dust shells (see Thé, Hageman, Westerlund, Tjin A Djie, 1985).

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