The massive star binary fraction in young open clusters – I. NGC 6231 revisited

Sana, H.; Gosset, Éric; Nazé, Yaël; Rauw, Grégor; Linder, N.

doi:10.1111/j.1365-2966.2008.13037.x

Cited by 130 publications

(172 citation statements)

References 52 publications

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“…>200 d & >40 d for 30 Dor and R136 proper; Schnurr et al 2008aSchnurr et al , 2009b) and the additional X-ray selected candidates. This is consistent with other surveys which find similarly high percentages for OB and Wolf-Rayet stars, albeit for different samples of stars comprising either lower (Clark et al 2008;Ritchie et al 2009) or a wider range of masses (Kobulnicky & Fryer 2007;Sana et al 2008;Bosch et al 2009). Such a binary fraction potentially presents important constraints on the formation mechanisms for very massive stars such as CXO J1745-28 and the Arches population.…”

Section: Discussion and Concluding Remarkssupporting

confidence: 81%

The binary nature of the Galactic centre X-ray source CXOGC J174536.1-285638

Clark

Crowther

Mikles

2009

A&A

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Context. The combination of X-ray and near-IR surveys of the central 2 o × 0.8 o of the Galactic centre have revealed a population of X-ray bright massive stars. However, the nature of the X-ray emission, originating in wind collision zones or via accretion onto compact objects, is uncertain. Aims. In order to address this we investigated the nature of one of the most luminous X-ray sources − CXOGC J174536.1-285638. Methods. This was accomplished by an analysis of the near-IR spectrum with a non-LTE model atmosphere code to determine the physical parameters of the primary.Results. This was found to be an highly luminous WN9h star, which is remarkably similar to the most massive stars found in the Arches cluster, for which comparison to evolutionary tracks suggest an age of 2-2.5 Myr and an initial mass of ∼110 M . The X-ray properties of CXOGC J174536.1-285638 also resemble those of 3 of the 4 X-ray detected WN9h stars within the Arches and in turn other very massive WNLh colliding wind binaries, of which WR25 forms an almost identical "twin". Simple analytical arguments demonstrate consistency between the X-ray emission and a putative WN9h+mid O V-III binary, causing us to favour such a scenario over an accreting binary. However, we may not exclude a high mass X-ray binary interpretation, which, if correct, would provide a unique insight into the (post-SN) evolution of extremely massive stars. Irrespective of the nature of the secondary, CXOGC J174536.1-285638 adds to the growing list of known and candidate WNLh binaries. Of the subset of WNLh stars subject to a radial velocity survey, we find a lower limit to the binary fraction of ∼45%; of interest for studies of massive stellar formation, given that they currently possess the highest dynamically determined masses of any type of star.

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Section: Discussion and Concluding Remarkssupporting

confidence: 81%

The binary nature of the Galactic centre X-ray source CXOGC J174536.1-285638

Clark

Crowther

Mikles

2009

A&A

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“…Levato et al (1988) revisited this question and reached more robust conclusions: OC stars usually do not show the radial velocity variations typical of spectroscopic binaries. Sana et al (2008) obtained time series spectroscopy of HD 152249 and did not detect any sign of a companion. The interferometric search for companions around O stars by Sana et al (2014) confirms that HD 152249, HD 152424, and HD 154811 do not have bright companions.…”

Section: Discussionmentioning

confidence: 99%

Surface abundances of OC supergiants

Martins

Foschino

Bouret

et al. 2016

A&A

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Context. Some O and B stars show unusually strong or weak lines of carbon and/or nitrogen. These objects are classified as OBN or OBC stars. It has recently been shown that nitrogen enrichment and carbon depletion are the most likely explanations for the existence of the ON class. Aims. We investigate OC stars (all being supergiants) to check that surface abundances are responsible for the observed anomalous line strengths. Methods. We perform a spectroscopic analysis of three OC supergiants using atmosphere models. A fourth star was previously studied by us. Our sample thus comprises all OC stars known to date in the Galaxy. We determine the stellar parameters and He, C, N, and O surface abundances. Results. We show that all stars have effective temperatures and surface gravities fully consistent with morphologically normal O supergiants. However, OC stars show little, if any, nitrogen enrichment and carbon surface abundances consistent with the initial composition. OC supergiants are thus barely chemically evolved, unlike morphologically normal O supergiants.

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“…Davis et al 2008), this is not necessarily the case for the high-mass stars originally present in the cluster. Sana et al (2008) and Mason et al (2009) find a minimum binary fraction of 60-75% for O stars associated with clusters or OB associations. In globular clusters, these fractions may even be higher.…”

Section: Mass Budgetmentioning

confidence: 99%

Massive binaries as the source of abundance anomalies in globular clusters

Mink

Pols

Langer

et al. 2009

A&A

435

427

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Abundance anomalies observed in globular cluster stars indicate pollution with material processed by hydrogen burning. Two main sources have been suggested: asymptotic giant branch (AGB) stars and massive stars rotating near the break-up limit (spin stars). We propose massive binaries as an alternative source of processed material. We compute the evolution of a 20 M star in a close binary considering the effects of non conservative mass and angular momentum transfer and of rotation and tidal interaction to demonstrate the principle. We find that this system sheds about 10 M of material, nearly the entire envelope of the primary star. The ejecta are enriched in He, N, Na, and Al and depleted in C and O, similar to the abundance patterns observed in gobular cluster stars. However, Mg is not significantly depleted in the ejecta of this model. In contrast to the fast, radiatively driven winds of massive stars, this material is typically ejected with low velocity. We expect that it remains inside the potential well of a globular cluster and becomes available for the formation or pollution of a second generation of stars. We estimate that the amount of processed low-velocity material ejected by massive binaries is greater than the contribution of AGB stars and spin stars combined, assuming that the majority of massive stars in a proto-globular cluster interact with a companion and return their envelope to the interstellar medium. If we take the possible contribution of intermediate mass stars in binaries into account and assume that the ejecta are diluted with an equal amount of unprocessed material, we find that this scenario can potentially provide enough material to form a second generation of low-mass stars, which is as numerous as the first generation of low-mass stars, without the need to make commonly adopted assumptions, such as preferential loss of the first generation of stars, external pollution of the cluster, or an anomalous initial mass function.

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The massive star binary fraction in young open clusters – I. NGC 6231 revisited

Cited by 130 publications

References 52 publications

The binary nature of the Galactic centre X-ray source CXOGC J174536.1-285638

The binary nature of the Galactic centre X-ray source CXOGC J174536.1-285638

Surface abundances of OC supergiants

Massive binaries as the source of abundance anomalies in globular clusters

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