Intensive photometry of southern Wolf-Rayet stars

Balona, L. A.; Egan, J.; Marang, F.

doi:10.1093/mnras/240.1.103

Cited by 39 publications

(25 citation statements)

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“…in the WR catalog, is suspected as a binary because of "diluted emission lines" and because Isserstedt et al (1983) found a photometric and spectroscopic period of 7.69 d. Balona et al (1989) could confirm the photometric variability, but found large scatter from a periodicity. Marchenko et al (1998b) could not even see any variability.…”

Section: Comments On Individual Starsmentioning

confidence: 96%

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The Galactic WN stars

Hamann¹,

Gräfener²,

Liermann³

2006

A&A

352

578

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Context. Very massive stars pass through the Wolf-Rayet (WR) stage before they finally explode. Details of their evolution have not yet been safely established, and their physics are not well understood. Their spectral analysis requires adequate model atmospheres, which have been developed step by step during the past decades and account in their recent version for line blanketing by the millions of lines from iron and iron-group elements. However, only very few WN stars have been re-analyzed by means of line-blanketed models yet. Aims. The quantitative spectral analysis of a large sample of Galactic WN stars with the most advanced generation of model atmospheres should provide an empirical basis for various studies about the origin, evolution, and physics of the Wolf-Rayet stars and their powerful winds. Methods. We analyze a large sample of Galactic WN stars by means of the Potsdam Wolf-Rayet (PoWR) model atmospheres, which account for iron line blanketing and clumping. The results are compared with a synthetic population, generated from the Geneva tracks for massive star evolution. Results. We obtain a homogeneous set of stellar and atmospheric parameters for the Galactic WN stars, partly revising earlier results. Conclusions. Comparing the results of our spectral analyses of the Galactic WN stars with the predictions of the Geneva evolutionary calculations, we conclude that there is rough qualitative agreement. However, the quantitative discrepancies are still severe, and there is no preference for the tracks that account for the effects of rotation. It seems that the evolution of massive stars is still not satisfactorily understood.

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Section: Comments On Individual Starsmentioning

confidence: 96%

“…WR 16 shows substantial, but not periodic photometric variability (Balona et al 1989), and polarimetric evidence of a non-spherical outflow (Schulte-Ladbeck 1994). The thermal radio spectral index (Dougherty & Williams 2000) and the nondetection of X-rays (Oskinova 2005) speak against binarity.…”

Section: Comments On Individual Starsmentioning

confidence: 99%

The Galactic WN stars

Hamann¹,

Gräfener²,

Liermann³

2006

A&A

352

578

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“…4 Two other dust WC9d stars -WR69 & 103 -have also been suggested to be short period binaries on the basis of periodic photometric variability. For the former star Marchenko et al (1998) report a 2.29 day periodicity from Hipparcos data but are unable to determine its origin (binarity or NRP), although earlier observations by Balona et al (1989) failed to identify this. Conversely, both the latter authors and Moffat et al (1986) report a ∼1.75 day photometric period for WR 103 which was not found in the Hipparcos dataset.…”

Section: Dust Production In Close Binariesmentioning

confidence: 99%

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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“…Therefore, no trace of the companion was detected, except perhaps for very weak auxiliary absorption components suspected on a few spectrograms (Conti et al 1979; but mainly Niemela 1979). However, it finally became clear that the companion should be detectable with the discovery (Balona et al 1989;Gosset et al 1991) that WR 22 exhibits an eclipse corresponding to the WR being in front of its companion. Only one eclipse occurs: the secondary one.…”

Section: The Massive Binary Wr 22mentioning

confidence: 99%

Phase-resolvedXMM-Newtonobservations of the massive WR+O binary WR 22

Gosset¹,

Nazé²,

Sana

et al. 2009

A&A

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Aims. To better understand the phenomenon of colliding winds in massive binary stars, we study the X-ray lightcurve of a WR+O system of the Carina region, a system well known for the high mass of its primary. Methods. Phase-resolved X-ray observations of the massive WR+O binary system WR 22 were performed with the XMM-Newton facility. We observed the object at seven different phases from near apastron to near periastron. Results. The X-ray spectrum can be represented by a two-component, optically thin, thermal plasma model with a first one at a typical temperature of 0.6 keV and a second hotter one in the range 2.0-4.5 keV. The hot component is indicative of a colliding wind phenomenon, but its flux is remarkably constant with time despite the high eccentricity of the orbit. Although surprising at first, this actually does not contradict the results of the hydrodynamical simulations of the wind collision that we performed. When the system goes from apastron to periastron, the soft part of the X-ray flux is progressively lowered by an increasing intervening absorbing column. This behaviour can be interpreted in terms of an X-ray emitting plasma located near the O star, but not fully intrinsic to it, and accompanying the star when it dives into the wind of the WR component. A model is presented that interprets most of the observational constraints. This model suggests that the mass-loss rate ofṀ WR ∼ 1.6 × 10 −5 M yr −1 assumed for the WR could still be slightly too high, whereas it is already lower than other published values. From the comparison of the observed and the expected absorptions at phases near periastron, we deduce that the hard X-ray emitting collision zone should at least have a typical size of 50-60 R , but that the size for the soft X-ray emitting region could reach 244 R if the assumed mass-loss rate is correct. We also present an upper limit to the X-ray luminosity of the WR component that further questions the existence of intrinsic X-ray emission from single WN stars.

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Intensive photometry of southern Wolf-Rayet stars

Cited by 39 publications

References 0 publications

The Galactic WN stars

The Galactic WN stars

A VLT/FLAMES survey for massive binaries in Westerlund 1

Phase-resolvedXMM-Newtonobservations of the massive WR+O binary WR 22

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