The Wolf-Rayet Population Predicted by Massive Single Star and Massive Binary Evolution

Vanbeveren, D.; Bever, J. Van; Belkus, Houria

doi:10.1086/519454

Cited by 82 publications

(87 citation statements)

References 18 publications

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“…Therefore, higher mass-loss rates in the WR phase would not bring the stellar evolution tracks into accordance with the empirical HRD positions of the SMC WN stars. We conclude that either the mass-loss in a pre-WR stage is significantly higher (via either continous mass-loss or episodic bursts), as suggested by e.g., Sander et al (2012) to explain the disagreement between WC stars and evolution models at Galactic metallicity (see also Vanbeveren et al 1998Vanbeveren et al , 2007Georgy 2012), or 4 In some cases the more recent description derived by Gräfener & Hamann (2008) is also used (e.g., Ekström et al 2012;Georgy et al 2013). , Brott et al 2011).…”

Section: Discussion Of the Evolutionary Statusmentioning

confidence: 92%

“…The effects of binary evolution on WR populations were studied by various authors (Paczyński 1967;Vanbeveren et al 2007;Eldridge et al 2008Eldridge et al , 2013. The initial mass required to enter the WR phase is considerably reduced, if angular momentum and mass transfer by Roche lobe overflow occurs in the course of the evolution.…”

Section: Discussion Of the Evolutionary Statusmentioning

confidence: 99%

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Wolf-Rayet stars in the Small Magellanic Cloud

Hainich

Pasemann

Todt

et al. 2015

A&A

111

159

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Context. Wolf-Rayet (WR) stars have a severe impact on their environments owing to their strong ionizing radiation fields and powerful stellar winds. Since these winds are considered to be driven by radiation pressure, it is theoretically expected that the degree of the wind mass-loss depends on the initial metallicity of WR stars. Aims. Following our comprehensive studies of WR stars in the Milky Way, M 31, and the LMC, we derive stellar parameters and massloss rates for all seven putatively single WN stars known in the SMC. Based on these data, we discuss the impact of a low-metallicity environment on the mass loss and evolution of WR stars. Methods. The quantitative analysis of the WN stars is performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. The physical properties of our program stars are obtained from fitting synthetic spectra to multi-band observations. Results. In all SMC WN stars, a considerable surface hydrogen abundance is detectable. The majority of these objects have stellar temperatures exceeding 75 kK, while their luminosities range from 10 5.5 to 10 6.1 L . The WN stars in the SMC exhibit on average lower mass-loss rates and weaker winds than their counterparts in the Milky Way, M 31, and the LMC. Conclusions. By comparing the mass-loss rates derived for WN stars in different Local Group galaxies, we conclude that a clear dependence of the wind mass-loss on the initial metallicity is evident, supporting the current paradigm that WR winds are driven by radiation. A metallicity effect on the evolution of massive stars is obvious from the HRD positions of the SMC WN stars at high temperatures and high luminosities. Standard evolution tracks are not able to reproduce these parameters and the observed surface hydrogen abundances. Homogeneous evolution might provide a better explanation for their evolutionary past.

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Section: Discussion Of the Evolutionary Statusmentioning

confidence: 92%

Section: Discussion Of the Evolutionary Statusmentioning

confidence: 99%

Wolf-Rayet stars in the Small Magellanic Cloud

Hainich

Pasemann

Todt

et al. 2015

A&A

111

159

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“…From the theoretical point of view, it is well known that strong mass loss during the RSG phase favours a bluewards evolution (Salasnich et al 1999;Vanbeveren et al 1998Vanbeveren et al , 2007 and thus helps in fulfilling one of the two minimal conditions for having a WR star, namely to have an effective temperature higher than about log(T eff /K) = 4.0. However, it is unclear whether this strong mass loss may lead to the formation of WC stars.…”

Section: Discussion Of Various Possible Origins For the Low-luminositmentioning

confidence: 99%

Grids of stellar models with rotation

Georgy

Ekström

Meynet

et al. 2012

A&A

305

364

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Context. In recent years, many very interesting observations have appeared concerning the positions of Wolf-Rayet (WR) stars in the Hertzsprung-Russell diagram (HRD), the number ratios of WR stars, the nature of Type Ibc supernova (SN) progenitors, long and soft gamma ray bursts (LGRB), and the frequency of these various types of explosive events. These observations represent key constraints on massive star evolution. Aims. We study, in the framework of the single-star evolutionary scenario, how rotation modifies the evolution of a given initial mass star towards the WR phase and how it impacts the rates of Type Ibc SNe. We also discuss the initial conditions required to obtain collapsars and LGRB. Methods. We used a recent grid of stellar models computed with and without rotation to make predictions concerning the WR populations and the frequency of different types of core-collapse SNe. Current rotating models were checked to provide good fits to the following features: solar luminosity and radius at the solar age, main-sequence width, red-giant and red-supergiant (RSG) positions in the HRD, surface abundances, and rotational velocities. Results. Rotating stellar models predict that about half of the observed WR stars and at least half of the Type Ibc SNe may be produced through the single-star evolution channel. Rotation increases the duration of the WNL and WNC phases, while reducing those of the WNE and WC phases, as was already shown in previous works. Rotation increases the frequency of Type Ic SNe. The upper mass limit for Type II-P SNe is ∼19.0 M for the non rotating models and ∼16.8 M for the rotating ones. Both values agree with observations. Moreover, present rotating models provide a very good fit to the progenitor of SN 2008ax. We discuss future directions of research for further improving the agreement between the models and the observations. We conclude that the mass-loss rates in the WNL and RSG phases are probably underestimated at present. We show that up to an initial mass of 40 M , a surface magnetic field inferior to about 200 G may be sufficient to produce some braking. Much lower values are needed at the red supergiant stage. We suggest that the presence/absence of any magnetic braking effect may play a key role in questions regarding rotation rates of young pulsars and the evolution leading to LGRBs.

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“…With our grids of helium star models, we provide an evolutionary test of this conclusion. Previous theoretical studies on the evolution of WR stars have considered the effects of rotation (Georgy et al 2012;Meynet & Maeder 2005) and duplicity (Vanbeveren et al 1998;Van Bever & Vanbeveren 2003;Vanbeveren, Van Bever & Belkus 2007;Eldridge et al 2013). Following Habets (1986) and Dewi et al (2002), we shall investigate the evolution of single helium star models.…”

Section: Introductionmentioning

confidence: 99%

Helium stars: towards an understanding of Wolf–Rayet evolution

McClelland

Eldridge

2016

Mon. Not. R. Astron. Soc.

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Wolf-Rayet (WR) stars are massive stars that have lost most or all of their hydrogen via powerful stellar winds. Recent observations have indicated that hydrogen-free WR stars have cooler temperatures than those predicted by current evolutionary models. To investigate how varying mass-loss rate affects WR evolution, we have created a grid of pure helium star models. We compare our results with Galactic and LMC WR observations and show that the temperature ranges of observed WR stars can be reproduced by varying the mass-loss rate, which effectively determines the size of the helium envelope around the core. We also find that WN and WO stars arise from more massive stars, whereas WC stars come from lower masses. This contradicts the standard Conti scenario by which WN and WC stars evolve in an age sequence. We also predict the magnitudes of our models at core-collapse and compare with observations of nearby progenitors of Type Ib/c supernovae. We confirm the findings of previous studies that suggest WR stars are the progenitors of core-collapse supernovae: the progenitors would remain unobserved except in the cases where the progenitor is a low-mass helium giant, as is the case of iPTF13bvn.

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The Wolf-Rayet Population Predicted by Massive Single Star and Massive Binary Evolution

Cited by 82 publications

References 18 publications

Wolf-Rayet stars in the Small Magellanic Cloud

Wolf-Rayet stars in the Small Magellanic Cloud

Grids of stellar models with rotation

Helium stars: towards an understanding of Wolf–Rayet evolution

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