The B[e] stars

AbstractB[e] supergiants show evidence for a non-spherical two-component stellar wind. The general appearance and the physical properties of the suggested disk-like configuration are discussed. The high mass-loss rates, the surprisingly large number and the location in the H-R diagram make these stars important for the understanding of the post-main-sequence evolution of massive stars.

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Formation of Ring Nebulae around Massive Stars in LMC HII Regions

Symposium - International Astronomical Union ◽

10.1017/s0074180900117644 ◽

1999 ◽

Vol 190 ◽

pp. 134-135

Author(s):

Kerstin Weis ◽

Wolfgang J. Duschl

Keyword(s):

Main Sequence ◽

Massive Stars ◽

Ambient Medium ◽

Hii Regions ◽

Large Magellanic Cloud ◽

High Mass ◽

Stellar Winds ◽

High Mass Loss ◽

Form Ring ◽

Ring Nebulae

Massive stars have strong stellar winds and consequently a high mass loss during their lifetimes. Therefore they can form ring nebulae by stellar winds sweeping up the ambient medium in the main sequence phase or through wind-wind interaction or eruptions in the evolved state. We present preliminary results of a search for single bubbles and ring-nebulae around massive stars in the Large Magellanic Cloud (LMC).

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Effects of a stochastic initial mass function on the upper main sequence band

International Astronomical Union Colloquium ◽

10.1017/s0252921100094914 ◽

1981 ◽

Vol 59 ◽

pp. 293-296

Author(s):

C. Chiosi ◽

L. Greggio

Keyword(s):

Mass Loss ◽

Effective Temperature ◽

Main Sequence ◽

Massive Stars ◽

Mass Function ◽

Initial Mass Function ◽

High Mass ◽

Initial Mass ◽

Sequence Band ◽

High Mass Loss

The theoretical (Mb versus Log Te) HR diagram for the brightest galactic OB stars shows an upper boundary for the luminosity, which is characterized by a decreasing luminosity with decreasing effective temperature (Humphreys and Davidson, 1979). The existence of this limit was interpreted by Chiosi et al. (1978) as due to the effect of mass loss by stellar wind on the evolution of most massive stars in core H-burning phase. In fact, evolutionary models calculated at constant mass cover a wider and wider range in effective temperature as the initial mass increases during the main sequence phase. On the contrary, sufficiently high mass-loss rates make the evolutionary sequences of most massive stars (M 60⩾Mʘ) shrink toward the zero age main sequence whenever, due to mass loss, CNO processed material is brought to the surface (Chiosi et al., 1978; de Loore et al., 1978; Maeder, 1980).

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The effects of Rotation on Wolf–Rayet Stars and on the Production of Primary Nitrogen by Intermediate Mass Stars

Symposium - International Astronomical Union ◽

10.1017/s007418090019624x ◽

2004 ◽

Vol 215 ◽

pp. 579-588 ◽

Cited By ~ 2

Author(s):

Georges Meynet ◽

Max Pettini

Keyword(s):

Star Formation ◽

Time Delay ◽

Main Sequence ◽

Massive Stars ◽

Sequence Evolution ◽

Stellar Rotation ◽

Intermediate Mass ◽

Intermediate Mass Stars ◽

Solar Metallicity ◽

Effects Of Rotation

We use the rotating stellar models described in the paper by A. Maeder & G. Meynet in this volume to consider the effects of rotation on the evolution of the most massive stars into and during the Wolf–Rayet phase, and on the post-Main Sequence evolution of intermediate mass stars. The two main results of this discussion are the following. First, we show that rotating models are able to account for the observed properties of the Wolf–Rayet stellar populations at solar metallicity. Second, at low metallicities, the inclusion of stellar rotation in the calculation of chemical yields can lead to a longer time delay between the release of oxygen and nitrogen into the interstellar medium following an episode of star formation, since stars of lower masses (compared to non-rotating models) can synthesize primary N. Qualitatively, such an effect may be required to explain the relative abundances of N and O in extragalactic metal–poor environments, particularly at high redshifts.

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Observational connections between LBV’s and other stars, with emphasis on Wolf-Rayet stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100004498 ◽

1989 ◽

Vol 113 ◽

pp. 229-240

Author(s):

A. F. J. Moffat ◽

L. Drissen ◽

C. Robert

Keyword(s):

Mass Loss ◽

Massive Stars ◽

Underlying Mechanism ◽

High Mass ◽

Strong Line ◽

Essential Step ◽

High Mass Loss ◽

Loss Rates ◽

R Domain

Abstract.We suggest that the LBV mechanism is an essential step to “force” massive stars (M(ZAMS) ≥ 40M⊙) to finally enter the Wolf-Rayet (W-R) domain in the Hertzsprung-Russel diagram (HRD). Just as massive supergiants showincreasingvariability as theyapproachthe Humphreys-Davidson (H-D)instability limit (horizontally in the HRD diagram), so the W-R stars showdecreasingvariability as theyrecede fromthe H-D limit (at first horizontally into the WNL domain, then, with their high mass loss rates, plunging irreversably downwards as ever hotter, smaller and fainter, strong-line W-R stars). Among the W-R stars, the luminous WNL subtypes (especially WN8) are the most variable, probably as a consequence of blob ejection in the wind. The underlying mechanism which triggers this ejection is possibly related to wind instabilities and may thus be quite different from the source of variability in luminous supergiants or LBV’s in quiescence, where photospheric effects dominate.

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Luminous Blue Variables, cool hypergiants and some impostors in the H-R diagram

Symposium - International Astronomical Union ◽

10.1017/s0074180900211625 ◽

2003 ◽

Vol 212 ◽

pp. 38-46

Author(s):

Roberta M. Humphreys

Keyword(s):

Magnetic Fields ◽

Mass Loss ◽

Surface Activity ◽

Massive Star ◽

Massive Stars ◽

High Mass ◽

Luminous Blue Variables ◽

Star Evolution ◽

High Mass Loss ◽

Massive Star Evolution

Current observations of the S Dor/LBVs and candidates and the implications for their important role in massive star evolution are reviewed. Recent observations of the cool hypergiants are altering our ideas about their evolutionary state, their atmospheres and winds, and the possible mechanisms for their asymmetric high mass loss episodes which may involve surface activity and magnetic fields. Recent results for IRC+10420, ρ Cas and VY CMa are highlighted. S Dor/LBVs in eruption, and the cool hypergiants in their high mass loss phases with their optically thick winds are not what their apparent spectra and temperatures imply; they are then ‘impostors’ on the H-R diagram. The importance of the very most massive stars, like η Carinae and the ‘supernovae impostors’ are also discussed.

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Theoretical evolution of massive stars with mass loss by stellar wind.

Symposium - International Astronomical Union ◽

10.1017/s007418090001370x ◽

1979 ◽

Vol 83 ◽

pp. 337-348 ◽

Cited By ~ 1

Author(s):

C. Chiosi ◽

E. Nasi ◽

G. Bertelli

Keyword(s):

Mass Loss ◽

Theoretical Models ◽

High Mass ◽

Main Sequence Stars ◽

Show Evidence ◽

High Mass Loss ◽

Mass Outflow ◽

Long Time ◽

Theoretical Evolution ◽

Hot Corona

Although it was known since a long time that very luminous blue and red stars may show evidence of mass outflow, it was the advent of the Copernicus satellite that clearly ascertained all OB supergiants (and also the most luminous main sequence stars) are losing mass at rates that are significant for their evolutionary history. The observational information for blue luminous stars (O, Of and WR) has been recently reviewed by Conti (1978), who discussed in some detail the data available for different spectral regions. The rates of mass loss inferred from these observations are estimated to be in the range 10−7 to 10−5 M⊙/yr for OB stars, and from 10−5 to 10−4 M⊙/yr for WR stars. Several theoretical models have been proposed to explain those high mass-loss rates, and the high terminal velocities ranging from 1000 to 3000 km/sec. The two basic models are: the cool radiation pressure model, originally proposed by Lucy and Solomon (1970) and elaborated by Castor et al. (1975), in which the envelope is accelerated by momentum transfer from radiation to ions due to the ultraviolet line absorption; and the coronal model of Thomas (1973), and Hearn (1975), where the wind is sustained by gas pressure in a hot corona around the star. As both models do not completely account for the observations, several complementary modifications have been suggested. The nowaday situation is reviewed by Cassinelli and Lamers (1978), and Conti (1978).

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Massive donors in interacting binaries: effect of metallicity

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037694 ◽

2020 ◽

Vol 638 ◽

pp. A55 ◽

Cited By ~ 7

Author(s):

Jakub Klencki ◽

Gijs Nelemans ◽

Alina G. Istrate ◽

Onno Pols

Keyword(s):

Mass Transfer ◽

Parameter Space ◽

Binary Systems ◽

Main Sequence ◽

Massive Stars ◽

First Episode ◽

Sequence Evolution ◽

Radial Expansion ◽

Solar Metallicity ◽

Order Of Magnitude

Metallicity is known to significantly affect the radial expansion of a massive star: the lower the metallicity, the more compact the star, especially during its post-main sequence evolution. Our goal is to study this effect in the context of binary evolution. Using the stellar-evolution code MESA, we computed evolutionary tracks of massive stars at six different metallicities between 1.0 Z⊙ and 0.01 Z⊙. We explored variations of factors known to affect the radial expansion of massive stars (e.g., semiconvection, overshooting, or rotation). Using observational constraints, we find support for an evolution in which already at a metallicity Z ≈ 0.2 Z⊙ massive stars remain relatively compact (∼100 R⊙) during the Hertzprung-gap (HG) phase and most of their expansion occurs during core-helium burning (CHeB). Consequently, we show that metallicity has a strong influence on the type of mass transfer evolution in binary systems. At solar metallicity, a case-B mass transfer is initiated shortly after the end of the main sequence, and a giant donor is almost always a rapidly expanding HG star. However, at lower metallicity, the parameter space for mass transfer from a more evolved, slowly expanding CHeB star increases dramatically. This means that envelope stripping and formation of helium stars in low-metallicity environments occurs later in the evolution of the donor, implying a shorter duration of the Wolf-Rayet phase (even by an order of magnitude) and higher final core masses. This metallicity effect is independent of the effect of metallicity-dependent stellar winds. At metallicities Z ≤ 0.04 Z⊙, a significant fraction of massive stars in binaries with periods longer than 100 days engages in the first episode of mass transfer very late into their evolution, when they already have a well-developed CO core. The remaining lifetime (≲104 yr) is unlikely to be long enough to strip the entire H-rich envelope. Cases of unstable mass transfer leading to a merger would produce CO cores that spin fast at the moment of collapse. We find that the parameter space for mass transfer from massive donors (> 40 M⊙) with outer convective envelopes is extremely small or even nonexistent. We briefly discuss this finding in the context of the formation of binary black hole mergers.

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