Nitrogen chronology of massive main sequence stars

Köhler, Karl; Borzyszkowski, Mikolaj; Brott, I.; Langer, N.; Koter, A. de

doi:10.1051/0004-6361/201118352

Cited by 15 publications

(19 citation statements)

References 22 publications

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“…Furthermore, the stars considered here are very close to their Eddington limit, which may affect their envelope structure (Köhler et al 2014) and give rise to instabilities , raising the question whether eruptive mass-loss, as observed e.g. for some LBVs and supernova progenitors, may also affect their evolution.…”

Section: Stellar Evolution In the Upper Hrdmentioning

confidence: 93%

“…E.g., for the extremely massive WNh stars R136a1, a2, a3 and c, Crowther et al (2010) Tables 3 and 4. A comparison with evolutionary models for VMS from Köhler et al (2014) gives values that are on average ∼30% lower. This is to be expected, in particular for O stars with H-rich surface compositions.…”

Section: Stellar Masses and Eddington Factorsmentioning

confidence: 98%

“…Using evolutionary masses from Köhler et al (2014) for the O-type stars with high hydrogen surface abundances the relation changes to log (Ṁ/ f v ) = (2.68 ± 0.44) × log Γ e − (4.29 ± 0.27). The slope is only slightly shallower and well within the errors bars.…”

Section: Mass-loss Near the Eddington Limitmentioning

confidence: 99%

“…11 and 12, distinguishing between different spectral types and surface compositions. They are compared with single star evolutionary tracks from Köhler et al (2014) with an initial rotational velocity of R,ini = 300 km s −1 . In agreement with our conclusions from Sect.…”

Section: Stellar Evolution In the Upper Hrdmentioning

confidence: 99%

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The VLT-FLAMES Tarantula Survey

Bestenlehner

Gräfener

Vink

et al. 2014

A&A

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The evolution and fate of very massive stars (VMS) is tightly connected to their mass-loss properties. Their initial and final masses differ significantly as a result of mass loss. VMS have strong stellar winds and extremely high ionising fluxes, which are thought to be critical sources of both mechanical and radiative feedback in giant H  regions. However, how VMS mass-loss properties change during stellar evolution is poorly understood. In the framework of the VLT-Flames Tarantula Survey (VFTS), we explore the mass-loss transition region from optically thin O star winds to denser WNh Wolf-Rayet star winds, thereby testing theoretical predictions. To this purpose we select 62 O, Of, Of/WN, and WNh stars, an unprecedented sample of stars with the highest masses and luminosities known. We perform a spectral analysis of optical VFTS as well as near-infrared VLT/SINFONI data using the non-LTE radiative transfer code CMFGEN to obtain both stellar and wind parameters. For the first time, we observationally resolve the transition between optically thin O star winds and optically thick hydrogen-rich WNh Wolf-Rayet winds. Our results suggest the existence of a "kink" between both mass-loss regimes, in agreement with recent Monte Carlo simulations. For the optically thick regime, we confirm the steep dependence on the classical Eddington factor Γ e from previous theoretical and observational studies. The transition occurs on the main sequence near a luminosity of 10 6.1 L , or a mass of 80 . . . 90 M . Above this limit, we find that -even when accounting for moderate wind clumping (with f v = 0.1) -wind mass-loss rates are enhanced with respect to standard prescriptions currently adopted in stellar evolution calculations. We also show that this results in substantial helium surface enrichment. Finally, based on our spectroscopic analyses, we are able to provide the most accurate ionising fluxes for VMS known to date, confirming the pivotal role of VMS in ionising and shaping their environments.

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Section: Stellar Evolution In the Upper Hrdmentioning

confidence: 93%

Section: Stellar Masses and Eddington Factorsmentioning

confidence: 98%

Section: Mass-loss Near the Eddington Limitmentioning

confidence: 99%

Section: Stellar Evolution In the Upper Hrdmentioning

confidence: 99%

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The VLT-FLAMES Tarantula Survey

Bestenlehner

Gräfener

Vink

et al. 2014

A&A

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153

253

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show abstract

“…Because of the sensitivity of evolutionary tracks in the H-R diagram with rotation, the location of massive mainsequence stars in the H-R diagram does not provide a unique determination of age and mass. Rotation thus introduces some degeneracy, but surface abundance patterns could help resolve this degeneracy (Brott et al 2011a;Köhler et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Massive stars at low metallicity

Bouret

Lanz

Martins

et al. 2013

A&A

102

160

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Aims. We aim to study the properties of massive stars at low metallicity, with an emphasis on their evolution, rotation, and surface abundances. We focus on O-type dwarfs in the Small Magellanic Cloud. These stars are expected to have weak winds that do not remove significant amounts of their initial angular momentum. Methods. We analyzed the UV and optical spectra of twenty-three objects using the NLTE stellar atmosphere code  and derived photospheric and wind properties. Results. The observed binary fraction of the sample is ≈26%, which is consistent with more systematic studies if one considers that the actual binary fraction is potentially larger owing to low-luminosity companions and that the sample was biased because it excluded obvious spectroscopic binaries. The location of the fastest rotators in the Hertzsprung-Russell (H-R) diagram built with fast-rotating evolutionary models and isochrones indicates that these could be several Myr old. The offset in the position of these fast rotators compared with the other stars confirms the predictions of evolutionary models that fast-rotating stars tend to evolve more vertically in the H-R diagram. Only one star of luminosity class Vz, expected to best characterize extreme youth, is located on the zero-age main sequence, the other two stars are more evolved. We found that the distribution of O and B stars in the (N) -v sin i diagram is the same, which suggests that the mechanisms responsible for the chemical enrichment of slowly rotating massive stars depend only weakly on the star's mass. We furthermore confirm that the group of slowly rotating N-rich stars is not reproduced by the evolutionary tracks. Even for more massive stars and faster rotators, our results call for stronger mixing in the models to explain the range of observed N abundances. All stars have an N/C ratio as a function of stellar luminosity that match the predictions of the stellar evolution models well. More massive stars have a higher N/C ratio than the less massive stars. Faster rotators show on average a higher N/C ratio than slower rotators, again consistent with the expected trend of stronger mixing as rotation increases. When comparing the N/O versus N/C ratios with those of stellar evolution models, the same global qualitative agreement is reached. The only discrepant behavior is observed for the youngest two stars of the sample, which both show very strong signs of mixing, which is unexpected for their evolutionary status.

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Magnetic main sequence stars as progenitors of blue supergiants

Petermann¹,

Castro²,

Langer³

2014

Proc. IAU

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Blue supergiants (BSGs) to the right the main sequence band in the HR diagram can not be reproduced by standard stellar evolution calculations. We investigate whether a reduced convective core mass due to strong internal magnetic fields during the main sequence might be able to recover this population of stars. We perform calculations with a reduced mass of the hydrogen burning convective core of stars in the mass range 3 − 30 M in a parametric way, which indeed lead to BSGs. It is expected that these BSGs would still show large scale magnetic fields in the order of 10 G.

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Nitrogen chronology of massive main sequence stars

Cited by 15 publications

References 22 publications

The VLT-FLAMES Tarantula Survey

The VLT-FLAMES Tarantula Survey

Massive stars at low metallicity

Magnetic main sequence stars as progenitors of blue supergiants

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