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

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.

scholarly journals Evolution of High Mass Stars

1986 ◽  
Vol 7 ◽  
pp. 475-479
Author(s):  
André Maeder
Keyword(s):  
Mass Loss ◽  
Massive Star ◽  
Massive Stars ◽  
High Mass ◽  
Stellar Winds ◽  
Star Evolution ◽  
Interstellar Material ◽  
Massive Star Evolution

Several properties of massive star evolution are of great interest for the understanding of young populations in galaxies: -the genetic connections predicted by the models for the various types of massive stars allow us to understand their filiation; -in order to study the differences of the relative star frequencies in galaxies, we have to know which properties affect the lifetimes in the various evolutionary stages; -the composition of stellar winds is interesting to discuss the wind injections into the interstellar material, particularly the injections by Wolf-Rayet stars, and to discuss the influence of mass loss on nucleosynthesis and chemical yields. Here we shall briefly summarize some recent results on these various problems. For more details the reader may refer to general reviews (cf. Humphreys, 1984; Maeder, 1984a,b; Chiosi and Maeder, 1986).

scholarly journals Massive Star Modeling and Nucleosynthesis

2021 ◽  
Vol 8 ◽  
Author(s):  
Sylvia Ekström
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Star ◽  
Nuclear Reactions ◽  
Massive Stars ◽  
Reaction Rates ◽  
Star Evolution ◽  
Structural Impact ◽  
Massive Star Evolution ◽  
The Impact

After a brief introduction to stellar modeling, the main lines of massive star evolution are reviewed, with a focus on the nuclear reactions from which the star gets the needed energy to counterbalance its gravity. The different burning phases are described, as well as the structural impact they have on the star. Some general effects on stellar evolution of uncertainties in the reaction rates are presented, with more precise examples taken from the uncertainties of the 12C(α, γ)16O reaction and the sensitivity of the s-process on many rates. The changes in the evolution of massive stars brought by low or zero metallicity are reviewed. The impact of convection, rotation, mass loss, and binarity on massive star evolution is reviewed, with a focus on the effect they have on the global nucleosynthetic products of the stars.

scholarly journals The Wolf-Rayet Connection - Luminous Blue Variables and Evolved Supergiants

1991 ◽  
Vol 143 ◽  
pp. 485-498
Author(s):  
Roberta M. Humphreys
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Physical Characteristics ◽  
High Mass ◽  
Luminous Blue Variables ◽  
Ir Stars ◽  
High Mass Loss ◽  
Stage 1 ◽  
And Behavior

The physical characteristics and behavior of evolved massive stars in three different mass ranges are reviewed with application to whether they may eventually evolve to the WR stage 1. >40-50 M⊙ as LBV's, 2. ∼30-40 M⊙ as cool hypergiant-OH/IR stars and 3. ∼10-30 M⊙ as red supergiant-OH/IR stars. I emphasize the importance of the relatively short but high mass loss phases as LBV's and as OH/IR stars in determining the fate of massive stars from 10 to 100 M⊙.

scholarly journals Evolution of Massive Stars with Rotation and Mass Loss

2004 ◽  
Vol 215 ◽  
pp. 500-509 ◽  
Author(s):  
André Maeder ◽  
Georges Meynet
Keyword(s):  
Mass Loss ◽  
Critical Velocity ◽  
Massive Star ◽  
Massive Stars ◽  
Initial Distribution ◽  
Dominant Effect ◽  
Star Evolution ◽  
Massive Star Evolution

Rotation appears as a dominant effect in massive star evolution. It largely affects all the model outputs: inner structure, tracks, lifetimes, isochrones, surface compositions, blue to red supergiant ratios, etc. At lower metallicities, the effects of rotational mixing are larger; also, more stars may reach critical velocity, even if the initial distribution of rotational velocities is the same.

scholarly journals Massive star evolution: from the early to the present day Universe

2008 ◽  
Vol 4 (S252) ◽  
pp. 317-327 ◽  
Author(s):  
Georges Meynet ◽  
Sylvia Ekström ◽  
Cyril Georgy ◽  
André Maeder ◽  
Raphael Hirschi
Keyword(s):  
Interstellar Medium ◽  
Mass Loss ◽  
Radiation Field ◽  
Massive Star ◽  
Massive Stars ◽  
Mechanical Energy ◽  
Axial Rotation ◽  
Star Evolution ◽  
Massive Star Evolution ◽  
Hr Diagram

AbstractMass loss and axial rotation are playing key roles in shaping the evolution of massive stars. They affect the tracks in the HR diagram, the lifetimes, the surface abundances, the hardness of the radiation field, the chemical yields, the presupernova status, the nature of the remnant, the mechanical energy released in the interstellar medium, etc. . . In this paper, after recalling a few characteristics of mass loss and rotation, we review the effects of these two processes at different metallicities. Rotation probably has its most important effects at low metallicities, while mass loss and rotation deeply affect the evolution of massive stars at solar and higher than solar metallicities.

scholarly journals The dynamics of red supergiant winds

2002 ◽  
Vol 206 ◽  
pp. 306-309
Author(s):  
Anita M. S. Richards ◽  
Raymond J. Cohen ◽  
Malcolm D. Gray ◽  
Koji Murakawa ◽  
Jeremy A. Yates ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
Supernova Remnant ◽  
Massive Star ◽  
Zeeman Splitting ◽  
Stellar Winds ◽  
Maser Emission ◽  
Star Evolution ◽  
Massive Star Evolution ◽  
Loss Rates

During the red supergiant (RSG) stage of massive star evolution, emission from dust and molecules allows the copious stellar winds to be studied in great detail. This help us understand not only the evolutionary stages of the star (which are highly dependent on mass loss rates), but also the morphology of the eventual supernova remnant. Maser emission from OH and H2O has been mapped with milli-arcsec resolution (using MERLIN and the EVN/global VLBI) around RSG including VY CMa, S Per and VX Sgr. The H2O masers originate in clouds accelerating away from the star and OH mainlines masers interleave the outer parts of the H2O maser shell. Zeeman splitting of OH maser lines reveals the orientation and strength of stellar-centred magnetic fields.

scholarly journals Metallicity Effects in Massive Star Evolution and Number Frequencies of WR Stars in Galaxies

1991 ◽  
Vol 143 ◽  
pp. 445-452
Author(s):  
André Maeder
Keyword(s):  
Mass Spectrum ◽  
Mass Loss ◽  
Massive Star ◽  
Massive Stars ◽  
Star Evolution ◽  
Massive Star Evolution ◽  
Loss Rates

The results of new grids of models of massive stars with metallicities Z = 0.002, 0.005, 0.020 and 0.040 and mass loss rates depending on Z are shown. When integrated over the mass spectrum, the models enable us to predict number ratios, such as WR/O, WC/WN, WNE/WR, WNL/WR, WCE/WR, WCL/WR, WO/WR as a function of Z in galaxies.Comparisons between models and observations in galaxies are made and show, as was suggested by Maeder, Lequeux and Azzopardi (1980), that the effects of metallicity on the mass loss rates are the prime agent responsible for the different distributions of massive stars in galaxies.

scholarly journals Red Supergiants, Yellow Hypergiants, and Post-RSG Evolution

Galaxies ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 92 ◽  
Author(s):  
Michael S. Gordon ◽  
Roberta M. Humphreys
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Terminal State ◽  
High Mass ◽  
Luminous Blue Variables ◽  
High Mass Loss ◽  
Red Supergiants ◽  
Wind Activity ◽  
Open Question ◽  
Hr Diagram

How massive stars end their lives remains an open question in the field of star evolution. While the majority of stars above ≳9 M ⊙ will become red supergiants (RSGs), the terminal state of these massive stars can be heavily influenced by their mass-loss histories. Periods of enhanced circumstellar wind activity can drive stars off the RSG branch of the HR Diagram. This phase, known as post-RSG evolution, may well be tied to high mass-loss events or eruptions as seen in the Luminous Blue Variables (LBVs) and other massive stars. This article highlights some of the recent observational and modeling studies that seek to characterize this unique class of stars, the post-RSGs and link them to other massive objects on the HR Diagram such as LBVs, Yellow Hypergiants and dusty RSGs.

scholarly journals The Formation of Massive Stars

2010 ◽  
Vol 6 (S270) ◽  
pp. 57-64
Author(s):  
Ian A. Bonnell ◽  
Rowan J Smith
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Massive Star ◽  
Massive Stars ◽  
Cluster Formation ◽  
High Mass ◽  
Prestellar Cores ◽  
Stellar Mergers ◽  
Massive Clusters ◽  
Viable Mechanism

AbstractThere has been considerable progress in our understanding of how massive stars form but still much confusion as to why they form. Recent work from several sources has shown that the formation of massive stars through disc accretion, possibly aided by gravitational and Rayleigh-Taylor instabilities is a viable mechanism. Stellar mergers, on the other hand, are unlikely to occur in any but the most massive clusters and hence should not be a primary avenue for massive star formation. In contrast to this success, we are still uncertain as to how the mass that forms a massive star is accumulated. there are two possible mechanisms including the collapse of massive prestellar cores and competitive accretion in clusters. At present, there are theoretical and observational question marks as to the existence of high-mass prestellar cores. theoretically, such objects should fragment before they can attain a relaxed, centrally condensed and high-mass state necessary to form massive stars. Numerical simulations including cluster formation, feedback and magnetic fields have not found such objects but instead point to the continued accretion in a cluster potential as the primary mechanism to form high-mass stars. Feedback and magnetic fields act to slow the star formation process and will reduce the efficiencies from a purely dynamical collapse but otherwise appear to not significantly alter the process.

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