A VLT/FLAMES survey for massive binaries in Westerlund 1

Ritchie, B. W.; Clark, J. S.; Negueruela, I.; Langer, N.

doi:10.1051/0004-6361/201014834

Cited by 51 publications

(103 citation statements)

References 38 publications

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“…If binary driven mass loss removes the H-rich mantle in -or shortly after -the main sequence, the He-rich core is exposed for a longer period of time than in single star evolution, allowing the enhanced WR mass loss rates to act for longer. This results in a lower pre-SN core mass and hence the likely formation of a neutron star rather than a black hole (Fryer et al 2002) as appears to be the case in Wd1 (Clark et al 2008;Ritchie et al 2010a). In contrast, a single star will retain its H-rich mantle for longer, be subject to WR mass loss rates for a shorter period of time and will likely yield a Black Hole in the mass range considered here (e.g.…”

Section: Evolutionary Pathways In Wd1mentioning

confidence: 82%

“…Unfortunately, while this transition is clear of any WR emission lines it does overlap the interstellar C 2 Phillips (2-0) R/Q bands, which are visible in our spectra of W239 and other cluster members, complicating analysis (cf. Ritchie et al 2010a). This region of the spectra is presented in Fig.…”

Section: Spectroscopymentioning

confidence: 99%

“…and W13 (WNVL+OB). To these we might also add, albeit with less certainty, W44 (WR L; WN9h) -which showed rapid, dramatic line profile variability for which binarity is the most compelling explanation ) -as well as the progenitor of the magnetar CXOU J164710.2-455216 (Ritchie et al 2010a). …”

Section: Evolutionary Pathways In Wd1mentioning

confidence: 99%

“…Another compelling target is the young (4-5 Myr) massive (∼10 5 M ) galactic cluster Westerlund 1 (Wd 1, Clark et al 2005), which contains a significant ( 100) population of massive (M initial > 30 M , Ritchie et al 2010a) stars. Multiwavelength observations of the cluster revealed a number of indirect binary markers amongst the OB supergiants and Wolf-Rayets (WR), with a binary fraction for the latter inferred to be at least 70% (and potentially consistent with unity, Crowther et al 2006a;Clark et al 2008;Dougherty et al 2010).…”

Section: Introductionmentioning

confidence: 99%

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A VLT/FLAMES survey for massive binaries in Westerlund 1

Clark

Ritchie

Negueruela

et al. 2011

A&A

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Context. There is growing evidence that a treatment of binarity amongst OB stars is essential for a full theory of stellar evolution. However the binary properties of massive stars -frequency, mass ratio & orbital separation -are still poorly constrained. Aims. In order to address this shortcoming we have undertaken a multiepoch spectroscopic study of the stellar population of the young massive cluster Westerlund 1. In this paper we present an investigation into the nature of the dusty Wolf-Rayet star and candidate binary W239. Methods. To accomplish this we have utilised our spectroscopic data in conjunction with multi-year optical and near-IR photometric observations in order to search for binary signatures. Comparison of these data to synthetic non-LTE model atmosphere spectra were used to derive the fundamental properties of the WC9 primary. Results. We found W239 to have an orbital period of only ∼5.05 days, making it one of the most compact WC binaries yet identified. Analysis of the long term near-IR lightcurve reveals a significant flare between 2004-6. We interpret this as evidence for a third massive stellar component in the system in a long period (>6 yr), eccentric orbit, with dust production occuring at periastron leading to the flare. The presence of a near-IR excess characteristic of hot (∼1300 K) dust at every epoch is consistent with the expectation that the subset of persistent dust forming WC stars are short (<1 yr) period binaries, although confirmation will require further observations. Non-LTE model atmosphere analysis of the spectrum reveals the physical properties of the WC9 component to be fully consistent with other Galactic examples. Conclusions. The simultaneous presence of both short period Wolf-Rayet binaries and cool hypergiants within Wd 1 provides compelling evidence for a bifurcation in the post-Main Sequence evolution of massive stars due to binarity. Short period O+OB binaries will evolve directly to the Wolf-Rayet phase, either due to an episode of binary mediated mass loss -likely via case A mass transfer or a contact configuration -or via chemically homogenous evolution. Conversely, long period binaries and single stars will instead undergo a red loop across the HR diagram via a cool hypergiant phase. Future analysis of the full spectroscopic dataset for Wd 1 will constrain the proportion of massive stars experiencing each pathway; hence quantifying the importance of binarity in massive stellar evolution up to and beyond supernova and the resultant production of relativistic remnants.

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Section: Evolutionary Pathways In Wd1mentioning

confidence: 82%

Section: Spectroscopymentioning

confidence: 99%

Section: Evolutionary Pathways In Wd1mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A VLT/FLAMES survey for massive binaries in Westerlund 1

Clark

Ritchie

Negueruela

et al. 2011

A&A

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“…periodic RV variability and/or hard, overluminous X-ray emission; Clark et al 2008;Ritchie et al 2010;and in prep.). Indeed, their spectral similarity (Figs.…”

Section: Evolutionary Pathways For Massive Stars In Wd1mentioning

confidence: 99%

A VLT/FLAMES survey for massive binaries in Westerlund 1

Clark

Ritchie

Najarro

et al. 2014

A&A

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Context. The first soft gamma-ray repeater was discovered over three decades ago, and was subsequently identified as a magnetar, a class of highly magnetised neutron star. It has been hypothesised that these stars power some of the brightest supernovae known, and that they may form the central engines of some long duration gamma-ray bursts. However there is currently no consenus on the formation channel(s) of these objects. Aims. The presence of a magnetar in the starburst cluster Westerlund 1 implies a progenitor with a mass ≥40 M , which favours its formation in a binary that was disrupted at supernova. To test this hypothesis we conducted a search for the putative pre-SN companion.Methods. This was accomplished via a radial velocity survey to identify high-velocity runaways, with subsequent non-LTE model atmosphere analysis of the resultant candidate, Wd1-5. Results. Wd1-5 closely resembles the primaries in the short-period binaries, Wd1-13 and 44, suggesting a similar evolutionary history, although it currently appears single. It is overluminous for its spectroscopic mass and we find evidence of He-and N-enrichement, O-depletion, and critically C-enrichment, a combination of properties that is difficult to explain under single star evolutionary paradigms. We infer a pre-SN history for Wd1-5 which supposes an initial close binary comprising two stars of comparable (∼41 M + 35 M ) masses. Efficient mass transfer from the initially more massive component leads to the mass-gainer evolving more rapidly, initiating luminous blue variable/common envelope evolution. Reverse, wind-driven mass transfer during its subsequent WC Wolf-Rayet phase leads to the carbon pollution of Wd1-5, before a type Ibc supernova disrupts the binary system. Under the assumption of a physical association between Wd1-5 and J1647-45, the secondary is identified as the magnetar progenitor; its common envelope evolutionary phase prevents spin-down of its core prior to SN and the seed magnetic field for the magnetar forms either in this phase or during the earlier episode of mass transfer in which it was spun-up. Conclusions. Our results suggest that binarity is a key ingredient in the formation of at least a subset of magnetars by preventing spin-down via core-coupling and potentially generating a seed magnetic field. The apparent formation of a magnetar in a Type Ibc supernova is consistent with recent suggestions that superluminous Type Ibc supernovae are powered by the rapid spin-down of these objects.

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Gravitationless black holes

Zhang

2011

Astrophys Space Sci

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A gravitationless black hole model is proposed in accord with a five-dimensional fully covariant KaluzaKlein (K-K) theory with a scalar field, which unifies the four-dimensional Einsteinian general theory of relativity and Maxwellian electromagnetic theory. It is shown that a dense compact core of a star, when it collapses to a critical density, suddenly turns off or shields its gravitational field. The core, if its mass exceeds an upper limit, directly collapses into a black hole. Otherwise, the extremely large pressure, as the gravity is turned off, immediately stops the collapse and drives the mantle material of supernova moving outward, which leads to an impulsive explosion and forms a neutron star as a remnant. A neutron star can further evolve into a black hole when it accretes enough matter from a companion star such that the total mass exceeds a lower limit. The black hole in the K-K theory is gravitationless at the surface because the scalar field is infinitely strong, which varies the equivalent gravitational constant to zero. In general, a star, at the end of its evolution, is relatively harder to collapse into a gravitationless K-K black hole than a strong gravitational Schwarzschild black hole. This is consistent with the observation of some very massive stars to form neutron stars rather than expected black holes. In addition, the gravitationless K-K black hole should be easier to generate jets than a Schwarzschild black hole.

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A VLT/FLAMES survey for massive binaries in Westerlund 1

Cited by 51 publications

References 38 publications

A VLT/FLAMES survey for massive binaries in Westerlund 1

A VLT/FLAMES survey for massive binaries in Westerlund 1

A VLT/FLAMES survey for massive binaries in Westerlund 1

Gravitationless black holes

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