Nitrogen line spectroscopy of O-stars

González, J. G. Rivero; Puls, J.; Najarro, F.; Brott, I.

doi:10.1051/0004-6361/201117790

Cited by 101 publications

(124 citation statements)

References 80 publications

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“…Our results qualititatively agree with those from Rivero-González et al (2012) for the LMC, who also obtained very high N and He abundances for a large fraction of their LMC sample. GHV-62024 would very nicely fit in Rivero-González et al Fig.…”

Section: The Evolutionary Status Of Ghv-62024supporting

confidence: 90%

A peculiar Of star in the Local Group galaxy IC 1613

Herrero¹,

García²,

Puls³

et al. 2012

A&A

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Context.Results from the theory of radiatively driven winds are nowadays incorporated in stellar evolutionary and population synthesis models, and are used in our interpretation of the observations of the deep Universe. Yet, the theory has been confirmed only until Small Magellanic Cloud metallicities. Observations and analyses of O-stars at lower metallicities are difficult, but much needed to prove the theory. Aims. We have observed GHV-62024, an O6.5 IIIf star in the low-metallicity galaxy IC 1613 (Z ≈ 0.15 Z ) to study its evolution and wind. According to a previous preliminary analysis that was subject to significant restrictions this star could challenge the radiatively driven wind theory at low metallicities. Here we present a complete analysis of this star. Methods. Our observations were obtained with VIMOS at VLT, at R ≈ 2000 and covered approximately between 4000 and 7000 Å. The observations were analysed using the latest version of the model atmosphere code FASTWIND, which includes the possibility of calculating the N iii spectrum. Results. We obtain the stellar parameters and conclude that the star follows the average wind momentum-luminosity relationship (WLR) expected for its metallicity, but with a high value for the exponent of the wind velocity law, β. Comparing this with values of other stars in the literature, we suggest that this high value may be reached because GHV-62024 could be a fast rotator seen at a low inclination angle. We also suggest that this could favour the appearance of the spectral "f"-characterictics. While the derived β value does not change by adopting a lower wind terminal velocity, we show that a wrong V ∞ has a clear impact on the position of the star in the WLR diagram. The N and He abundances are very high, consistent with strong CNO mixing that could have been caused by the fast rotation, although we cannot discard a different origin with present data. Stellar evolutionary model predictions are consistent with the star being still a fast rotator. We find again the well-known mass-discrepancy for this star. Conclusions. We conclude that the star follows the WLR expected for its metallicity. The results are consistent with GHV-62024 being a fast rotator seen close to pole-on, strongly contaminated at the surface with CNO products and with a wind structure altered by the fast rotation but without modifying the global WLR. We suggest that this could be a general property of fast rotators.

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Section: The Evolutionary Status Of Ghv-62024supporting

confidence: 90%

A peculiar Of star in the Local Group galaxy IC 1613

Herrero¹,

García²,

Puls³

et al. 2012

A&A

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“…However, simulations of LMC early B-type stars made by Brott et al (2011b) failed to reproduce the remaining 40%, which are split into two different groups of stars, one containing slowly rotating, nitrogen-enriched objects and another one containing rapidly rotating un-enriched objects. The analysis of Rivero González et al (2012) also indicated a large number of O-type stars in the LMC with large enrichment in nitrogen and with a low rotation rate, supporting the same conclusions as for the B stars in the LMC. These authors stressed, however, that the problem of the group containing the highly-enriched slow-rotating stars was more severe for the O-type star population than for the B-type star one.…”

Section: The N Contentsupporting

confidence: 68%

A spectroscopic investigation of the O-type star population in four Cygnus OB associations

Mahy

Rauw

Becker

et al. 2015

A&A

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Aims. Having established the binary status of nineteen O-type stars located in four Cygnus OB associations, we now determine their fundamental parameters to constrain their properties and their evolutionary status. We also investigate their surface nitrogen abundances, which we compare with other results from the literature obtained for galactic O-type stars. Methods. Using optical spectra collected for each object in our sample and some UV data from the archives, we apply the CMFGEN atmosphere code to determine their main properties. For the binary systems, we have disentangled the components to obtain their individual spectra and investigate them as if they were single stars. Results. We find that the distances of several presumably single O-type stars seem poorly constrained because their luminosities are not in agreement with the "standard" luminosities of stars with similar spectral types. The ages of these O-type stars are all less than 7 Myr. Therefore, the ages of these stars agree with those, quoted in the literature, of the four associations, except for Cyg OB8 for which the stars seem older than the association itself. However, we point out that the distance of certain stars is debatable relative to values found in the literature. The N content of these stars put in perspective with N contents of several other galactic O-type stars seems to draw the same five groups as found in the "Hunter" diagram for the O and B-type stars in the LMC even though their locations are obviously different. We determine mass-loss rates for several objects from the Hα line and UV spectra. Finally, we confirm the "mass discrepancy" especially for O stars with masses smaller than 30 M .

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“…-Rotational velocity: V sin i is obtained by the Fourier transform method (Gray 1976;Simón-Díaz & Herrero 2007 fected by winds. Thanks to the good quality of the data and the relatively large number of diagnostic lines, the typical uncertainty on our determinations is 1000 K. -Surface gravity: the wings of Balmer lines are the main diagnostic of log g. Because of the échelle nature of our spectra, the normalization around Balmer lines was difficult.…”

Section: Atmosphere Models and Spectroscopic Analysismentioning

confidence: 99%

“…Compared with B stars, non-LTE effects are much stronger and line formation is harder to reproduce in atmosphere models (Rivero González et al 2011;Martins & Hillier 2012). Rivero González et al (2012) determined nitrogen abundances of LMC O stars. Their sample was limited to 20 objects, but they seemed to find a large population of N-rich slow rotators as is found among B stars.…”

Section: Introductionmentioning

confidence: 99%

The MiMeS survey of magnetism in massive stars: CNO surface abundances of Galactic O stars

Martins¹,

Hervé²,

Bouret³

et al. 2015

A&A

116

241

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Context. The evolution of massive stars is still partly unconstrained. Mass, metallicity, mass loss, and rotation are the main drivers of stellar evolution. Binarity and the magnetic field may also significantly affect the fate of massive stars. Aims. Our goal is to investigate the evolution of single O stars in the Galaxy. Methods. For that, we used a sample of 74 objects comprising all luminosity classes and spectral types from O4 to O9.7. We relied on optical spectroscopy obtained in the context of the MiMeS survey of massive stars. We performed spectral modelling with the code CMFGEN. We determined the surface properties of the sample stars, with special emphasis on abundances of carbon, nitrogen, and oxygen. Results. Most of our sample stars have initial masses in the range of 20 to 50 M . We show that nitrogen is more enriched and carbon and oxygen are more depleted in supergiants than in dwarfs, with giants showing intermediate degrees of mixing. CNO abundances are observed in the range of values predicted by nucleosynthesis through the CNO cycle. More massive stars, within a given luminosity class, appear to be more chemically enriched than lower mass stars. We compare our results with predictions of three types of evolutionary models and show that for two sets of models, 80% of our sample can be explained by stellar evolution including rotation. The effect of magnetism on surface abundances is unconstrained. Conclusions. Our study indicates that in the 20−50 M mass range, the surface chemical abundances of most single O stars in the Galaxy are fairly well accounted for by stellar evolution of rotating stars.

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Nitrogen line spectroscopy of O-stars

Cited by 101 publications

References 80 publications

A peculiar Of star in the Local Group galaxy IC 1613

A peculiar Of star in the Local Group galaxy IC 1613

A spectroscopic investigation of the O-type star population in four Cygnus OB associations

The MiMeS survey of magnetism in massive stars: CNO surface abundances of Galactic O stars

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