Evolution of surface CNO abundances in massive stars

Maeder, A.; Przybilla, N.; Nieva, M. F.; Georgy, Cyril; Meynet, Georges; Ekström, Sylvia; Eggenberger, P.

doi:10.1051/0004-6361/201220602

Cited by 88 publications

(126 citation statements)

References 56 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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“…A recent study (Maeder et al 2014) of the N/C vs. N/O plot, or similar plots like Fig. 2, shows that the slope for moderate CNO burning is model independent.…”

Section: The [O/n] Vs [C/n] Relation For Cemp-no Starsmentioning

confidence: 57%

The first stars: CEMP-no stars and signatures of spinstars

Maeder

Meynet

Chiappini

2015

A&A

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Aims. The CEMP-no stars are "carbon-enhanced-metal-poor" stars that in principle show no evidence of s-and r-elements from neutron captures. We try to understand the origin and nucleosynthetic site of their peculiar CNO, Ne-Na, and Mg-Al abundances. Methods. We compare the observed abundances to the nucleosynthetic predictions of AGB models and of models of rotating massive stars with internal mixing and mass loss. We also analyze the different behaviors of α-and CNO-elements, as well the abundances of elements involved in the Ne-Na and Mg-Al cycles. Results. We show that CEMP-no stars exhibit products of He-burning that have gone through partial mixing and processing by the CNO cycle, producing low 12 C/ 13 C and a broad variety of We show that back-and-forth, partial mixing between the He-and H-regions may account for this variety. Some s-elements, mainly of the first peak, may even be produced by these processes in a small fraction of the CEMP-no stars. We propose a classification scheme for the CEMP-no and low-s stars, based on the changes in composition produced by these successive back-and-forth mixing motions.

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“…The sample stars are marked according to the numbering scheme introduced in Table 1. (Przybilla et al 2010;Maeder et al 2014), see Fig. 14 of NP12. For a verification of the catalytic nature of the CNO cycles we also provide the sum of carbon, nitrogen and oxygen abundances in Table 1.…”

Section: Quantitative Spectroscopy Of the Sample Starsmentioning

confidence: 99%

Fundamental properties of nearby single early B-type stars

Nieva

Przybilla

2014

A&A

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Aims. Fundamental parameters of a sample of 26 apparently slowly-rotating single early B-type stars in OB associations and in the field within a distance of 400 pc from the Sun are presented and compared to high-precision data from detached eclipsing binaries (DEBs). Together with surface abundances for light elements the data are used to discuss the evolutionary status of the stars in context of the most recent Geneva grid of models for core hydrogen-burning stars in the mass-range ∼6 to 18 M at metallicity Z = 0.014. Methods. The fundamental parameters are derived on the basis of accurate and precise atmospheric parameters determined earlier by us from non-LTE analyses of high-quality spectra of the sample stars, utilising the new Geneva stellar evolution models. Results. Evolutionary masses plus radii and luminosities are determined to better than typically 5%, 10%, and 20% uncertainty, respectively, facilitating the mass−radius and mass−luminosity relationships to be recovered for single core hydrogen-burning objects with a similar precision as derived from DEBs. Good agreement between evolutionary and spectroscopic masses is found. Absolute visual and bolometric magnitudes are derived to typically ∼0.15−0.20 mag uncertainty. Metallicities are constrained to better than 15−20% uncertainty and tight constraints on evolutionary ages of the stars are provided. Overall, the spectroscopic distances and ages of individual sample stars agree with independently derived values for the host OB associations. Signatures of mixing with CN-cycled material are found in 1/3 of the sample stars. Typically, these are consistent with the amount predicted by the new Geneva models with rotation. The presence of magnetic fields appears to augment the mixing efficiency. In addition, a few objects are possibly the product of binary evolution. In particular, the unusual characteristics of τ Sco point to a blue straggler nature, due to a binary merger. Conclusions. The accuracy and precision achieved in the determination of fundamental stellar parameters from the quantitative spectroscopy of single early B-type stars comes close (within a factor 2-4) to data derived from DEBs. While our fundamental parameters are in good agreement with those derived from DEBs as a function of spectral type, significant systematic differences with data from the astrophysical reference literature are found. Masses are ∼10−20% and radii ∼25% lower then the recommended values for luminosity class V, resulting in the stars being systematically fainter than assumed usually, by ∼0.5 mag in absolute visual and bolometric magnitude. Our sample of giants is too small to derive firm conclusions, but similar trends as for the dwarfs are indicated.

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Evolution of surface CNO abundances in massive stars

Cited by 88 publications

References 56 publications

Surface abundances of ON stars

Surface abundances of ON stars

The first stars: CEMP-no stars and signatures of spinstars

Fundamental properties of nearby single early B-type stars

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