Mixing of CNO-cycled matter in massive stars

Przybilla, N.; Firnstein, M.; Nieva, M. F.; Meynet, Georges; Maeder, A.

doi:10.1051/0004-6361/201014164

Cited by 139 publications

(185 citation statements)

References 42 publications

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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: 63%

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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Section: Introductionsupporting

confidence: 63%

Surface abundances of ON stars

Martins

Simón‐Díaz

Palacios

et al. 2015

A&A

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“…The only peculiarities are enhanced nitrogen abundances in several sample stars, which can be understood in the framework of mixing of CN-cycled material into the atmospheric layers (see e.g. Przybilla et al 2010). The silicon abundance in object 5 is also conspicuously low, which may be an indicator for the onset of chemical differentiation in the otherwise normal star.…”

Section: Chemical Abundancesmentioning

confidence: 99%

Present-day cosmic abundances

Nieva

Przybilla²

2012

A&A

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Context. Early B-type stars are ideal indicators for present-day cosmic abundances since they preserve their pristine abundances and typically do not migrate far beyond their birth environments over their short lifetimes, in contrast to older stars like the Sun. They are also unaffected by depletion onto dust grains, unlike the cold/warm interstellar medium (ISM) or H ii regions. Aims. A carefully selected sample of early B-type stars in OB associations and the field within the solar neighbourhood is studied comprehensively. Quantitative spectroscopy is used to characterise their atmospheric properties in a self-consistent way. Present-day abundances for the astrophysically most interesting chemical elements are derived in order to investigate whether a present-day cosmic abundance standard can be established. Methods. High-resolution and high-S/N FOCES, FEROS and ELODIE spectra of well-studied sharp-lined early B-type stars are analysed in non-LTE. Line-profile fits based on extensive model grids and an iterative analysis methodology are used to constrain stellar parameters and elemental abundances at high accuracy and precision. Atmospheric parameters are derived from the simultaneous establishment of independent indicators, from multiple ionization equilibria and the Stark-broadened hydrogen Balmer lines, and they are confirmed by reproduction of the stars' global spectral energy distributions. Results. Effective temperatures are constrained to 1-2% and surface gravities to less than 15% uncertainty, along with accurate rotational, micro-and macroturbulence velocities. Good agreement of the resulting spectroscopic parallaxes with those from the new reduction of the Hipparcos catalogue is obtained. Absolute values for abundances of He, C, N, O, Ne, Mg, Si and Fe are determined to better than 25% uncertainty. The synthetic spectra match the observations reliably over almost the entire visual spectral range. Three sample stars, γ Ori, o Per and θ 1 Ori D, are identified as double-lined, indicating the presence of an early/mid B-type companion. Conclusions. A present-day cosmic abundance standard is established from a sample of 29 early B-type stars, indicating abundance fluctuations of less than 10% around the mean. Our results (i) resolve the long-standing discrepancy between a chemical homogeneous gas-phase ISM and a chemically inhomogeneous young stellar component out to several hundred parsec from the Sun, (ii) facilitate the amount of heavy elements locked up in the interstellar dust to be constrained precisely -the results imply that carbonaceous dust is largely destroyed inside the Orion H ii region, unlike the silicates, and that graphite is only a minority species in interstellar dust -, (iii) show that the mixing of CNO-burning products in the course of massive star evolution follows tightly the predicted nuclear path, (iv) provide reliable present-day reference points for anchoring Galactic chemical evolution models to observation, and (v) imply that the Sun has migrated outwards from the inne...

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“…Figure 6 shows the nitrogen surface abundance as a function of rotational velocity. The results of Morel et al (2008), Hunter et al (2008) and Przybilla et al (2010) have been added for comparison (small symbols). The following comments can be made.…”

Section: Chemical Evolution and Rotationmentioning

confidence: 99%

A quantitative study of O stars in NGC 2244 and the Monoceros OB2 association

Martins

Mahy

Hillier

et al. 2012

A&A

103

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Aims. Our goal is to determine the stellar and wind properties of seven O stars in the cluster NGC 2244 and three O stars in the OB association Mon OB2. These properties give us insight into the mass loss rates of O stars. They allow us to both check the validity of rotational mixing in massive stars and to better understand the effects of the ionizing flux and wind mechanical energy release on the surrounding interstellar medium and its influence on triggered star formation. Methods. We collected optical and UV spectra of the target stars that we analyzed by means of atmosphere models computed with the code CMFGEN. The spectra of binary stars were disentangled and the components studied separately. Results. All stars have an evolutionary age less than 5 million years, with the most massive stars being among the youngest. Nitrogen surface abundances show no clear relation with projected rotational velocities. Binaries and single stars show the same range of enrichment. This is attributed to the youth and/or wide separation of the binary systems in which the components have not (yet) experienced strong interaction. A clear trend toward greater enrichment in higher luminosity objects is observed, consistent with what evolutionary models with rotation predict for a population of O stars at any given age. We confirm the weakness of winds in late O dwarfs. In general, mass loss rates derived from UV lines are lower than mass loss rates obtained from Hα. The UV mass loss rates are even lower than the single-line driving limit in the latest type dwarfs. These issues are discussed in the context of the structure of massive stars winds. The evolutionary and spectroscopic masses are in agreement above 25 M , but the uncertainties are large. Below this threshold, the few late-type O stars studied here indicate that the mass discrepancy still seems to hold.

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Mixing of CNO-cycled matter in massive stars

Cited by 139 publications

References 42 publications

Surface abundances of ON stars

Surface abundances of ON stars

Present-day cosmic abundances

A quantitative study of O stars in NGC 2244 and the Monoceros OB2 association

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