Is macroturbulent broadening in OB Supergiants related to pulsations?

Uytterhoeven, K.; Herrero, A.; Castro, N.; Puls, J.; Aerts, C.

doi:10.1002/asna.201011459

Cited by 5 publications

(3 citation statements)

References 33 publications

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“…Aerts et al (2009) notably suggested that non-radial pulsations could trigger large-scale motions (hence macroturbulence), but this needs to be confirmed by a study covering a wider parameter space. A study by Simón-Díaz et al (2010) also showed that the amplitude of macroturbulence was correlated to the amplitude of line profile variability in a sample of OB supergiants. In practice, we introduce macroturbulence by convolving our rotationally broadened synthetic spectra with a Gaussian profile, thus mimicking isotropic turbulence.…”

Section: Modellingmentioning

confidence: 89%

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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Section: Modellingmentioning

confidence: 89%

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

Mahy

Rauw

Becker

et al. 2015

A&A

View full text Add to dashboard Cite

show abstract

“…Aerts et al (2009) recently suggested that non-radial pulsations could trigger large-scale motions (hence macroturbulence), but this needs to be confirmed by a study covering a wider parameter space. A recent study by Simón-Díaz et al (2010) showed that the amplitude of macroturbulence was correlated to the amplitude of line profile variability in a sample of OB supergiants.…”

Section: Modellingmentioning

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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“…Though the physical origin of this broadening still remains to be proven, there are some strong indications that it is associated with (high order, non-radial) stellar pulsations (Aerts et al 2009;Simón-Díaz et al 2010). To account for this effect, we used a radial-tangential description of v mac to fit the profile shapes of nitrogen (and partly helium) lines, using our first estimates on the stellar and wind parameters (see above) and the new v sin i values.…”

Section: Determination Of Stellar and Wind Parametersmentioning

confidence: 99%

Nitrogen line spectroscopy of O-stars

González

Puls

Najarro

et al. 2012

A&A

Self Cite

101

107

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Context. Nitrogen is a key element for testing the impact of rotational mixing on evolutionary models of massive stars. Recent studies of the nitrogen surface abundance in B-type stars within the VLT-FLAMES survey of massive stars have challenged part of the corresponding predictions. To obtain a more complete picture of massive star evolution, and to allow for additional constraints, these studies need to be extended to O-stars. Aims. This is the second paper in a series aiming at the analysis of nitrogen abundances in O-type stars, to establish tighter constraints on the early evolution of massive stars. In this paper, we investigate the N ivλ4058 emission line formation, provide nitrogen abundances for a substantial O-star sample in the Large Magellanic Cloud, and compare our (preliminary) findings with recent predictions from stellar evolutionary models. Methods. Stellar and wind parameters of our sample stars were determined by line profile fitting of hydrogen, helium and nitrogen lines, exploiting the corresponding ionization equilibria. Synthetic spectra were calculated by means of the NLTE atmosphere/spectrum synthesis code fastwind, using a new nitrogen model atom. We derived nitrogen abundances for 20 O-and 5 B-stars by analyzing all nitrogen lines (from different ionization stages) present in the available optical spectra. Results. The dominating process responsible for emission at N ivλ4058 in O-stars is the strong depopulation of the lower level of the transition, which increases as a function ofṀ. Unlike the N iii triplet emission, resonance lines do not play a role for typical mass-loss rates and below. We find (almost) no problem in fitting the nitrogen lines, in particular the "f" features. Only for some objects, where lines from N iii/N iv/N v are visible in parallel, we need to opt for a compromise solution. For five objects in the early B-/late O-star domain that have been previously analyzed by different methods and model atmospheres, we derive consistent nitrogen abundances. The bulk of our sample O-stars seems to be strongly nitrogen-enriched, and a clear correlation of nitrogen and helium enrichment is found. By comparing the nitrogen abundances as a function of v sin i ("Hunter-plot") with tailored evolutionary calculations, we identify a considerable number of highly enriched objects at low rotation. Conclusions. Our findings seem to support the basic outcome of previous B-star studies within the VLT-FLAMES survey. Owing to the low initial abundance, the detection of strong nitrogen enrichment in the bulk of O-stars indicates that efficient mixing takes place already during the very early phases of stellar evolution of LMC O-stars. For tighter constraints, however, upcoming results from the VLT-FLAMES Tarantula survey need to be waited for, which will comprise a much higher number of O-stars that will be analyzed based on similar methods as presented here.

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Is macroturbulent broadening in OB Supergiants related to pulsations?

Cited by 5 publications

References 33 publications

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

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

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

Nitrogen line spectroscopy of O-stars

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