scholarly journals Grids of stellar models with rotation

2019 ◽  
Vol 627 ◽  
pp. A24 ◽  
Author(s):  
J. H. Groh ◽  
S. Ekström ◽  
C. Georgy ◽  
G. Meynet ◽  
A. Choplin ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Stellar Winds ◽  
Pulsation Period ◽  
Instability Strip ◽  
Helium Burning ◽  
Red Supergiants ◽  
Low Metallicity ◽  
Effects Of Rotation ◽  
The Impact

The effects of rotation on stellar evolution are particularly important at low metallicity, when mass loss by stellar winds diminishes and the surface enrichment due to rotational mixing becomes relatively more pronounced than at high metallicities. Here we investigate the impact of rotation and metallicity on stellar evolution. Using similar physics as in our previous large grids of models at Z = 0.002 and Z = 0.014, we compute stellar evolution models with the Geneva code for rotating and nonrotating stars with initial masses (Mini) between 1.7 and 120 M⊙ and Z = 0.0004 (1/35 solar). This is comparable to the metallicities of the most metal poor galaxies observed so far, such as I Zw 18. Concerning massive stars, both rotating and nonrotating models spend most of their core-helium burning phase with an effective temperature higher than 8000 K. Stars become red supergiants only at the end of their lifetimes, and few red supergiants are expected. Our models predict very few to no classical Wolf–Rayet stars as a results of weak stellar winds at low metallicity. The most massive stars end their lifetimes as luminous blue supergiants or luminous blue variables, a feature that is not predicted by models with higher initial metallicities. Interestingly, due to the behavior of the intermediate convective zone, the mass domain of stars producing pair-instability supernovae is smaller at Z = 0.0004 than at Z = 0.002. We find that during the main sequence (MS) phase, the ratio between nitrogen and carbon abundances (N/C) remains unchanged for nonrotating models. However, N/C increases by factors of 10–20 in rotating models at the end of the MS. Cepheids coming from stars with Mini >  4 − 6 M⊙ are beyond the core helium burning phase and spend little time in the instability strip. Since they would evolve towards cooler effective temperatures, these Cepheids should show an increase of the pulsation period as a function of age.

scholarly journals Stellar evolution models at the Magellanic Cloud metallicities

2008 ◽  
Vol 4 (S256) ◽  
pp. 337-342
Author(s):  
Raphael Hirschi ◽  
Sylvia Ekström ◽  
Cyril Georgy ◽  
Georges Meynet ◽  
André Maeder
Keyword(s):  
Stellar Evolution ◽  
Gamma Ray ◽  
Massive Stars ◽  
Gamma Ray Bursts ◽  
Magellanic Clouds ◽  
Observational Constraints ◽  
Surface Enrichment ◽  
First Stars ◽  
Effects Of Rotation ◽  
The Impact

AbstractThe Magellanic Clouds are great laboratories to study the evolution of stars at two metallicities lower than solar. They provide excellent testbeds for stellar evolution theory and in particular for the impact of metallicity on stellar evolution. It is important to test stellar evolution models at metallicities lower than solar in order to use the models to predict the evolution and properties of the first stars. In these proceedings, after recalling the effects of metallicity, we present stellar evolution models including the effects of rotation at the Magellanic Clouds metallicities. We then compare the models to various observations (ratios of sub-groups of massive stars and supernovae, nitrogen surface enrichment and gamma-ray bursts) and show that the models including the effects of rotation reproduce most of the observational constraints.

scholarly journals Common envelope evolution of massive stars

2018 ◽  
Vol 14 (S346) ◽  
pp. 449-454 ◽  
Author(s):  
Paul M. Ricker ◽  
Frank X. Timmes ◽  
Ronald E. Taam ◽  
Ronald F. Webbink
Keyword(s):  
Black Hole ◽  
Stellar Evolution ◽  
Massive Stars ◽  
Evolution Theory ◽  
Helium Burning ◽  
Massive Black Hole ◽  
Common Envelope ◽  
Binary Black Hole ◽  
Low Metallicity ◽  
The Common

AbstractThe discovery via gravitational waves of binary black hole systems with total masses greater than 60Mʘ has raised interesting questions for stellar evolution theory. Among the most promising formation channels for these systems is one involving a common envelope binary containing a low metallicity, core helium burning star with mass ⁓30 – 40Mʘ and a black hole with mass ⁓30 – 40Mʘ. For this channel to be viable, the common envelope binary must eject more than half the giant star’s mass and reduce its orbital separation by as much as a factor of 80. We discuss issues faced in numerically simulating the common envelope evolution of such systems and present a 3D AMR simulation of the dynamical inspiral of a low-metallicity red supergiant with a massive black hole companion.

scholarly journals Bimodal regime in young massive clusters leading to subsequent stellar generations

2015 ◽  
Vol 12 (S316) ◽  
pp. 294-301
Author(s):  
Richard Wünsch ◽  
Jan Palouš ◽  
Guillermo Tenorio-Tagle ◽  
Casiana Muñoz-Tuñón ◽  
Soňa Ehlerová
Keyword(s):  
Stellar Evolution ◽  
Column Density ◽  
First Generation ◽  
Massive Stars ◽  
Ionising Radiation ◽  
Cluster Center ◽  
Stellar Winds ◽  
Hot Gas ◽  
Massive Clusters ◽  
By Products

AbstractMassive stars in young massive clusters insert tremendous amounts of mass and energy into their surroundings in the form of stellar winds and supernova ejecta. Mutual shock-shock collisions lead to formation of hot gas, filling the volume of the cluster. The pressure of this gas then drives a powerful cluster wind. However, it has been shown that if the cluster is massive and dense enough, it can evolve in the so–called bimodal regime, in which the hot gas inside the cluster becomes thermally unstable and forms dense clumps which are trapped inside the cluster by its gravity. We will review works on the bimodal regime and discuss the implications for the formation of subsequent stellar generations. The mass accumulates inside the cluster and as soon as a high enough column density is reached, the interior of the clumps becomes self-shielded against the ionising radiation of stars and the clumps collapse and form new stars. The second stellar generation will be enriched by products of stellar evolution from the first generation, and will be concentrated near the cluster center.

scholarly journals ENHANCED MASS LOSS RATES IN RED SUPERGIANTS AND THEIR IMPACT ON THE CIRCUMSTELLAR MEDIUM

2019 ◽  
Vol 55 (2) ◽  
pp. 161-175
Author(s):  
L. Hernández-Cervantes ◽  
B. Pérez-Rendón ◽  
A. Santillán ◽  
G. García-Segura ◽  
C. Rodríguez-Ibarra
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Gas Dynamics ◽  
Numerical Experiments ◽  
Evolutionary Models ◽  
Solar Composition ◽  
Red Supergiants ◽  
The Impact ◽  
Circumstellar Medium ◽  
Loss Rates

In this work, we present models of massive stars between 15 and 23 M⊙ , with enhanced mass loss rates during the red supergiant phase. Our aim is to explore the impact of extreme red supergiant mass-loss on stellar evolution and on their circumstellar medium. We computed a set of numerical experiments, on the evolution of single stars with initial masses of 15, 18, 20 and, 23 M⊙ , and solar composition (Z = 0.014), using the numerical stellar code BEC. From these evolutionary models, we obtained time-dependent stellar wind parameters, that were used explicitly as inner boundary conditions in the hydrodynamical code ZEUS-3D, which simulates the gas dynamics in the circumstellar medium (CSM), thus coupling the stellar evolution to the dynamics of the CSM. We found that stars with extreme mass loss in the RSG phase behave as a larger mass stars.

scholarly journals Massive stars in their death throes

2008 ◽  
Vol 366 (1884) ◽  
pp. 4441-4452 ◽  
Author(s):  
John J Eldridge
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Evolution Theory ◽  
Luminous Blue Variables ◽  
Show Evidence ◽  
Red Supergiants ◽  
Working Backwards

The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently, there are eight detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants, as theory has long predicted. However, no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae, which, given the expected progenitors, is an unlikely result. Also, observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict the current stellar evolution theory. This suggests that we may need to update our understanding.

scholarly journals The Wolf–Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud

2019 ◽  
Vol 627 ◽  
pp. A151 ◽  
Author(s):  
T. Shenar ◽  
D. P. Sablowski ◽  
R. Hainich ◽  
H. Todt ◽  
A. F. J. Moffat ◽  
...  
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Stars ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Binary Interaction ◽  
Evolutionary Status ◽  
X Ray ◽  
Composite Spectra ◽  
The Impact

Context. Massive Wolf–Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z ≈ 0.5 Z⊙), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf–Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45  ±  30% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only ≈12  ±  7% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises ≈4% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L ≈ 5.2 [L⊙], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (veq ≲ 250 km s−1) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.

scholarly journals Massive stars burning helium: the numbers of WR stars and red supergiants in galaxies

1981 ◽  
Vol 59 ◽  
pp. 283-287
Author(s):  
A. Maeder
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Short Note ◽  
Evolutionary Models ◽  
Helium Burning ◽  
Red Supergiants ◽  
Low Mass ◽  
Age Sequence ◽  
Carbon Burning ◽  
Loss Rates

We have calculated evolutionary models of massive stars in the range 15-120 Mʘ from the zero-age sequence up to the end of the carbon burning stage (Maeder, 1981). Three sets of models with different mass loss rates Ṁ have been computed; the adopted parametrisation of Ṁ is fitted on the observations and thus the expression for Ṁ differs according to the location of the stars in the HRD.In this short note we concentrate on the location of the He-burning stars in the HRD. The helium burning phase, which lasts 8 to 10% of the MS phase, is spent mainly as red supergiants (RSG) and as WR stars (note that for low mass loss, the time spent as A-G supergiants becomes longer).

scholarly journals Massive stars: stellar models and stellar yields, impact on Galactic Archaeology

2017 ◽  
Vol 13 (S334) ◽  
pp. 170-177
Author(s):  
Georges Meynet ◽  
Arthur Choplin ◽  
Sylvia Ekström ◽  
Cyril Georgy
Keyword(s):  
Magnetic Fields ◽  
Mass Loss ◽  
Massive Stars ◽  
Stellar Winds ◽  
Stellar Models ◽  
The Impact

AbstractThe physics of massive stars depends (at least) on convection, mass loss by stellar winds, rotation, magnetic fields and multiplicity. We briefly discuss the impact of the first three processes on the stellar yields trying to identify some guidelines for future works.

scholarly journals Stellar Evolution at Low Metallicity

2007 ◽  
Vol 3 (S250) ◽  
pp. 217-230 ◽  
Author(s):  
Raphael Hirschi ◽  
Cristina Chiappini ◽  
Georges Meynet ◽  
André Maeder ◽  
Sylvia Ekström
Keyword(s):  
Mass Loss ◽  
Gamma Ray ◽  
Massive Stars ◽  
Early Evolution ◽  
Strong Mixing ◽  
Strong Impact ◽  
Rotating Stars ◽  
Low Metallicity ◽  
The Impact ◽  
The Universe

AbstractMassive stars played a key role in the early evolution of the Universe. They formed with the first halos and started the re-ionisation. It is therefore very important to understand their evolution. In this review, we first recall the effect of metallicity (Z) on the evolution of massive stars. We then describe the strong impact of rotation induced mixing and mass loss at very low Z. The strong mixing leads to a significant production of primary 14N, 13C and 22Ne. Mass loss during the red supergiant stage allows the production of Wolf-Rayet stars, type Ib,c supernovae and possibly gamma-ray bursts (GRBs) down to almost Z = 0 for stars more massive than 60 M⊙. Galactic chemical evolution models calculated with models of rotating stars better reproduce the early evolution of N/O, C/O and 12C/13C. Finally, the impact of magnetic fields is discussed in the context of GRBs.

scholarly journals The excess of cool supergiants from contemporary stellar evolution models defies the metallicity-independent Humphreys-Davidson limit

2021 ◽  
Author(s):  
Avishai Gilkis ◽  
Tomer Shenar ◽  
Varsha Ramachandran ◽  
Adam S Jermyn ◽  
Laurent Mahy ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Rotation Rates ◽  
Mixing Parameters ◽  
Synthetic Populations ◽  
The Galaxy ◽  
Effective Temperatures ◽  
The Impact

Abstract The Humphreys-Davidson (HD) limit empirically defines a region of high luminosities (log10(L/L⊙) ≳ 5.5) and low effective temperatures (Teff ≲ 20 kK) on the Hertzsprung-Russell Diagram in which hardly any supergiant stars are observed. Attempts to explain this limit through instabilities arising in near- or super-Eddington winds have been largely unsuccessful. Using modern stellar evolution we aim to re-examine the HD limit, investigating the impact of enhanced mixing on massive stars. We construct grids of stellar evolution models appropriate for the Small and Large Magellanic Clouds (SMC, LMC), as well as for the Galaxy, spanning various initial rotation rates and convective overshooting parameters. Significantly enhanced mixing apparently steers stellar evolution tracks away from the region of the HD limit. To quantify the excess of over-luminous stars in stellar evolution simulations we generate synthetic populations of massive stars, and make detailed comparisons with catalogues of cool (Teff ≤ 12.5 kK) and luminous (log10(L/L⊙) ≥ 4.7) stars in the SMC and LMC. We find that adjustments to the mixing parameters can lead to agreement between the observed and simulated red supergiant populations, but for hotter supergiants the simulations always over-predict the number of very luminous (log10(L/L⊙) ≥ 5.4) stars compared to observations. The excess of luminous supergiants decreases for enhanced mixing, possibly hinting at an important role mixing has in explaining the HD limit. Still, the HD limit remains unexplained for hotter supergiants.

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