Properties of Galactic early-type O-supergiants

Bouret, Jean-Claude; Hillier, D. J.; Lanz, T.; Fullerton, A. W.

doi:10.1051/0004-6361/201118594

Cited by 172 publications

(378 citation statements)

References 124 publications

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“…The reason for this discrepancy is not known at present. Similar problems were noted by Bouret et al (2012). The derived parameters are gathered in Table 3.…”

Section: Stellar Parameterssupporting

confidence: 69%

Evidence of quasi-chemically homogeneous evolution of massive stars up to solar metallicity

Martins

Depagne

Russeil

et al. 2013

A&A

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Context. Long soft gamma-ray bursts (LGRBs) are usually associated with the death of the most massive stars. A large amount of core angular momentum in the phases preceding the explosion is required to form LGRBs. A very high initial rotational velocity can provide this angular momentum. This velocity strongly influences the way the star evolves: it is mixed in a chemically homogeneous way and evolves directly towards the blue part of the Hertzsprung-Russell (HR) diagram from the main sequence. Aims. We have shown that chemically homogeneous evolution takes place in the Small Magellanic Cloud (SMC) at low metallicity. We want to see whether there is a metallicity threshold above which such an evolution is not possible. Methods. We performed a spectroscopic analysis of H-rich early-type WN stars in the Large Magellanic Cloud (LMC) and the Galaxy. We used the code CMFGEN to determine the fundamental properties (T eff , L) and the surface composition of the target stars. We then placed the stars in the HR diagram and determined their evolution. Results. We show that both the LMC and Galactic WNh stars we selected cannot be explained by standard stellar evolution. They are located on the left of the main sequence but show surface abundances typical of CN equilibrium. In addition, they still contain a large amount of hydrogen. They are thus core-H burning objects. Their properties are consistent with chemically homogeneous evolution. We determine the metallicity of the Galactic stars from their position and Galactic metallicity gradients and conclude that they have 0.6 < Z < 1.0. A moderate coupling between the core and the envelope is required to explain that stellar winds do not extract too much angular momentum to prevent a blueward evolution. Conclusions. We have shown that chemically homogeneous evolution takes place in environments with metallicity up to solar. Since some long gamma-ray bursts appear in (super-)solar environments, such an evolution may be a viable way to form them over a wide range of metallicities.

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“…The reason for this discrepancy is not known at present. Similar problems were noted by Bouret et al (2012). The derived parameters are gathered in Table 3.…”

Section: Stellar Parameterssupporting

confidence: 69%

Evidence of quasi-chemically homogeneous evolution of massive stars up to solar metallicity

Martins

Depagne

Russeil

et al. 2013

A&A

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“…Hunter et al (2008Hunter et al ( , 2009 show that the majority of the B stars they studied in the Galaxy, Large and Small Magellanic Clouds exhibit nitrogen enrichments as predicted by rotating models, although a non-negligible fraction (20 to 40%) were found to be more enriched than expected for their rotation speed. Przybilla et al (2010) and Maeder et al (2014) demonstrate that B stars show surface CNO patterns consistent with the expectations of nucleosynthesis, and Martins et al (2015) reached similar conclusions for a large sample of Galactic single O stars (see also Bouret et al 2012Bouret et al , 2013.…”

Section: Introductionsupporting

confidence: 65%

Surface abundances of ON stars

Martins

Simón‐Díaz

Palacios

et al. 2015

A&A

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Context. Massive stars burn hydrogen through the CNO cycle during most of their evolution. When mixing is efficient or when mass transfer in binary systems occurs, chemically processed material is observed at the surface of O and B stars. Aims. ON stars show stronger lines of nitrogen than morphologically normal counterparts. Whether this corresponds to the presence of material processed through the CNO cycle is not known. Our goal is to answer this question. Methods. We performed a spectroscopic analysis of a sample of ON stars with atmosphere models. We determined the fundamental parameters as well as the He, C, N, and O surface abundances. We also measured the projected rotational velocities. We compared the properties of the ON stars to those of normal O stars. Results. We show that ON stars are usually rich in helium. Their CNO surface abundances are fully consistent with predictions of nucleosynthesis. ON stars are more chemically evolved and rotate − on average − faster than normal O stars. Evolutionary models including rotation cannot account for the extreme enrichment observed among ON main sequence stars. Some ON stars are members of binary systems, but others are single stars as indicated by stable radial velocities. Mass transfer is therefore not a simple explanation for the observed chemical properties. Conclusions. We conclude that ON stars show extreme chemical enrichment at their surface, consistent with nucleosynthesis through the CNO cycle. Its origin is not clear at present.

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“…Stellar and wind parameters are taken from: (1) Oskinova et al (2007); (2) Bouret et al (2012); (3) Puls et al (2006). Spectral type of HD 66811 is taken from Walborn et al (2009).…”

Section: Introductionmentioning

confidence: 99%

“…They also reduced the mass-loss rates in order to weaken the UV resonance lines, while the Hα emission is kept at the observed strength by adopting extremely large clumping factors up to D = 100. As an additional means to achieve a consistent fit, Bouret et al (2012) reduced the phosphorus abundances to values that are lower by a factor 1.4 to 5.1 than the solar abundance according to Asplund (2005). However, subsolar abundances for O stars are not expected and have no justification.…”

Section: Introductionmentioning

confidence: 99%

Macroclumping as solution of the discrepancy between Hαand P v mass loss diagnostics for O-type stars

Šurlan

Hamann

Aret

et al. 2013

A&A

110

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Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Hα emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims. In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from O4 to O7) and test whether the reported discrepancies can be resolved this way. Methods. In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Hα emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles.Results. Our results show that with the mass-loss rates that fit Hα (and other Balmer and He ii lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions.Macroclumping resolves the previously reported discrepancy between Hα and P v mass-loss diagnostics.

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Properties of Galactic early-type O-supergiants

Cited by 172 publications

References 124 publications

Evidence of quasi-chemically homogeneous evolution of massive stars up to solar metallicity

Evidence of quasi-chemically homogeneous evolution of massive stars up to solar metallicity

Surface abundances of ON stars

Macroclumping as solution of the discrepancy between Hαand P v mass loss diagnostics for O-type stars

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