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 Evolution of the Precursor of SN 1987 A

1988 ◽  
Vol 108 ◽  
pp. 408-409
Author(s):  
André Maeder
Keyword(s):  
Mass Loss ◽  
Massive Star ◽  
Essential Property ◽  
Solar Mass ◽  
Star Evolution ◽  
Final Mass ◽  
The Galaxy ◽  
Age Sequence ◽  
Massive Star Evolution ◽  
Hr Diagram

SummaryIdeally, the evolutionary models for the precursor of SN 1987 A should account for both the SN properties and the observational constraints for massive stars with relevant mass and composition.Mass loss is an essential property of massive star evolution. Recent parametrisations of mass loss rates for galactic stars cover the whole HR diagram. There are indications that for given L and Teff values, is lower at lower metallicity and therefore is lower in the LMC than in the Galaxy, thus we take with f < 1. Various models of an intitial 20 M⊙ star with f=0.2, 0.4, 0.6 and 1.0 are constructed (cf. Fig. 1) with a metallicity Z=0.006 and a moderate overshooting dover=0.3 Hp. From these models, we suggest an initial mass on the zero age sequence of 17 to 18 M⊙. The pre-SN location in the HR diagram very much depends on the remaining stellar mass, or more precisely on the mass of the remaining H-rich envelope. A final location at log Teff ≃ 4.2 is obtained for a final mass of about 9.0 M⊙ (cf. Fig.1). Scaled to an initial value of 17 M⊙, this corresponds to a final mass of about 8 M⊙ and a remaining H-rich envelope of a few tenths of a solar mass at most. The stellar surface exhibits CNO equilibrium values with C/N ≃ 0.01 and O/N ≃ 0.1 in mass fraction, and an hydrogen content X (surf) = 0.39. The blue progenitor is obtained for f=0.4, i.e. for -values in the LMC equal to 40% of the galactic values.

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 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 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 The Cooler Supergiants (A to M): Crucial Signposts in the Lifecycles of Massive Stars

1986 ◽  
Vol 116 ◽  
pp. 45-59
Author(s):  
Roberta M. Humphreys
Keyword(s):  
Massive Star ◽  
Massive Stars ◽  
Stability Limit ◽  
Hydrogen Burning ◽  
Stellar Objects ◽  
Star Evolution ◽  
Different Types ◽  
The Stability ◽  
Massive Star Evolution ◽  
Hr Diagram

The intermediate and late-type supergiants are the visually brightest stars. They are among the first stellar objects observed in other galaxies and provide our first clues to the conditions of massive star evolution in galaxies of different types. They are not as massive as the hottest and most luminous stars in the upper left of the HR diagram. Nevertheless, these somewhat lower mass stars (≈20−50 M⊙) with relatively cool temperatures play a major role in our efforts to understand massive star evolution. These supergiants are usually considered to be post hydrogen burning stars, and their relative numbers in the HR diagram provide essential comparisons with models for the later stages of massive star evolution. Most importantly, the most luminous cooler supergiants define the stability limit for massive stars in the HR diagram.

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 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 DDO68-V1: an extremely metal-poor LBV in a void galaxy

2018 ◽  
Vol 14 (S344) ◽  
pp. 392-395
Author(s):  
Yulia Perepelitsyna ◽  
Simon Pustilnik
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
Rare Event ◽  
Local Universe ◽  
Hii Region ◽  
V Band ◽  
Star Evolution ◽  
Low Metallicity ◽  
Massive Star Evolution

AbstractThe lowest metallicity massive stars in the Local Universe with $Z\sim \left( {{Z}_{\odot }}/50-{{Z}_{\odot }}/30 \right)$ are the crucial objects to test the validity of assumptions in the modern models of very low-metallicity massive star evolution. These models, in turn, have major implications for our understanding of galaxy and massive star formation in the early epochs. DDO68-V1 in a void galaxy DDO68 is a unique extremely metal-poor massive star. Discovered by us in 2008 in the HII region Knot3 with $Z={{Z}_{\odot }}/35\,\left[ 12+\log \left( \text{O/H} \right)\sim 7.14 \right]$, DDO68-V1 was identified as an LBV star. We present here the LBV lightcurve in V band, combining own new data and the last archive and/or literature data on the light of Knot3 over the 30 years. We find that during the years 2008-2011 the LBV have experienced a very rare event of ‘giant eruption’ with V-band amplitude of 4.5 mag ($V\sim {{24.5}^{m}}-{{20}^{m}}$).

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