(Intrinsic) Variations of Wolf-Rayet Stars

Genderen, A. M. van; Verheijen, Marc; Kampen, E. van; Robijn, F. H. A.; Heiden, R. van der; Esch, B.P.M. van; Greidanus, H.; Poole, R. S. Le; Reijns, R. A.; Hucht, K. A. van der; Schwarz, H. E.; Loore, C. W. H. De; Kuulkers, E.; Spijkstra, L.

doi:10.1007/978-94-011-3306-7_27

Cited by 17 publications

(6 citation statements)

References 7 publications

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“…Similar variability was observed by van Genderen et al (1990), and the variations were at first attributed to the WR-type primary. However, van Genderen et al (1991) considered the possibility that the B0-type secondary is a β Cephei star and derived 0.1385 ± 0.0002 d ( f = 7.22 d −1 ) for the period of the photometric variations. Owing to the evident variability, the star was named V1035 Sco (Kazarovets & Samus 1997).…”

Section: Appendix A: Notes On Individual Starssupporting

confidence: 77%

β Cephei stars in the ASAS-3 data

Pigulski¹,

Pojmański²

2007

A&A

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Aims. We analyse V-filter ASAS-3 photometry of 41 known β Cephei-type stars. The ASAS-3 photometry is combined with the archival data, if available, to determine long-term stability of periods and amplitudes of excited modes. Methods. Frequencies of modes are derived by means of Fourier periodograms with consecutive prewhitening. The results are examined in the context of detection threshold. Results. We detected amplitude changes in three β Cephei stars, BW Cru, V836 Cen, and V348 Nor. Period changes were found in KK Vel and V836 Cen. Our analysis shows that intrinsic period changes are more common among multiperiodic stars, apparently because they are caused by some kind of mode interaction. In addition, we found new modes for seven stars, and for ten others we provide new solutions or remove ambiguities in the detected frequencies. One candidate hybrid β Cephei/SPB star, HD 133823, is discovered.

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Section: Appendix A: Notes On Individual Starssupporting

confidence: 77%

β Cephei stars in the ASAS-3 data

Pigulski¹,

Pojmański²

2007

A&A

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“…As the author cautions, the dataset present by Shylaja (1990) for WR 14 is insufficient to derive a period and so its identification as a binary is highly uncertain. Likewise Veen & Wieringa (2000) cast serious doubt upon the photometric variability suggested for WR 50 by van Genderen et al (1991). Finally, Paardekooper et al (2002) show that the periodicity associated with WR86 is instead attributable to a β-Cephei companion.…”

Section: Possible Binary Pathwaysmentioning

confidence: 97%

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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“…He i is absent since helium is fully ionized, whereas hydrogen remains completely undetected, implying the use of zero-hydrogen models (Marchenko et al 2000;Crowther et al 1995). Various photometric studies of WR 46 have been undertaken (Smith 1968;Monderen et al 1988;van Genderen et al 1990van Genderen et al , 1991 up to the detailed photometric study of Veen et al (2002a), which reveals the full complexity of the WR 46 lightcurve. The star seems to vary with a 6.8 h (0.28 d) period that exhibits two maxima of rather similar brightness and two possibly different minima.…”

Section: Introductionmentioning

confidence: 99%

XMM-Newtonobservation of the enigmatic object WR 46

Gosset

Becker

Nazé

et al. 2011

A&A

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Aims. To further investigate the nature of the enigmatic object WR 46 and better understand the X-ray emission in massive stars and in their evolved descendants, we observed this variable object for more than two of its supposed cycles. The X-ray emission characteristics are appropriate indicators of the difference between a genuine Wolf-Rayet star and a specimen of a super soft source as sometimes suggested in the literature. The X-ray emission analysis might contribute to understanding the origin of the emitting plasma (intrinsically shocked wind, magnetically confined wind, colliding winds, and accretion onto a white dwarf or a more compact object) and to substantiating the decision about the exact nature of the star. Methods. The X-ray observations of WR 46 were performed with the XMM-Newton facility over an effective exposure time of about 70 ks.Results. Both the X-ray luminosity of WR 46, typical of a Wolf-Rayet star, and the existence of a relatively hard component (including the Fe-K line) rule out the possibility that WR 46 could be classified as a super soft source, and instead favour the Wolf-Rayet hypothesis. The X-ray emission of the star turns out to be variable below 0.5 keV but constant at higher energies. The soft variability is associated to the Wolf-Rayet wind, but revealing its deep origin necessitates additional investigations. It is the first time that such a variability is reported for a Wolf-Rayet star. Indeed, the X-ray emission exhibits a single-wave variation with a typical timescale of 7.9 h which could be related to the period observed in the visible domain both in radial velocities (single-wave) and in photometry (double-wave). The global X-ray emission seems to be dominated by lines and is closely reproduced by a three-temperature, optically thin, thermal plasma model. The derived values are 0.1−0.2 keV, 0.6 keV, and ∼4 keV, which indicates that a wide range of temperatures is actually present. The soft emission part could be related to a shocked-wind phenomenon. The hard tail of the spectrum cannot presently be explained by such an intrinsic phenomenon as a shocked wind and instead suggests there is a wind-wind collision zone, as does the relatively high L X /L bol ratio. We argue that this scenario implies the existence of an object farther away from the WN3 object than any possible companion in an orbit related to the short periodicity.

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(Intrinsic) Variations of Wolf-Rayet Stars

Cited by 17 publications

References 7 publications

β Cephei stars in the ASAS-3 data

β Cephei stars in the ASAS-3 data

A VLT/FLAMES survey for massive binaries in Westerlund 1

XMM-Newtonobservation of the enigmatic object WR 46

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