The chaotic wind of WR 40 as probed by BRITE

Tahina Ramiaramanantsoa, Richard Ignace, Anthony F.J. Moffat, Nicole St-Louis, Evgenya L. Shkolnik, Adam Popowicz, Rainer Kuschnig, Andrzej Pigulski, Gregg A. Wade, Gerald Handler, Herbert Pablo, Konstanze Zwintz

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Among Wolf-Rayet stars, those of subtype WN8 are the intrinsically most variable. We have explored the long-term photometric variability of the brightest known WN8 star, WR 40, through four contiguous months of time-resolved, single-passband optical photometry with the BRIght Target Explorer nanosatellite mission. The Fourier transform of the observed light curve reveals that the strong light variability exhibited by WR 40 is dominated by many randomly triggered, transient, low-frequency signals. We establish a model in which the whole wind consists of stochastic clumps following an outflow visibility promptly rising to peak brightness upon clump emergence from the optically thick pseudo-photosphere in the wind, followed by a gradual decay according to the right-half of a Gaussian. Free electrons in each clump scatter continuum light from the star. We explore a scenario where the clump size follows a power-law distribution, and another one with an ensemble of clumps of constant size. Both scenarios yield simulated light curves morphologically resembling the observed light curve remarkably well, indicating that one cannot uniquely constrain the details of clump size distribution with only a photometric light curve. Nevertheless, independent evidence favours a negative-index power law, as seen in many other astrophysical turbulent media.

Original languageEnglish (US)
Pages (from-to)5921-5930
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Dec 1 2019


  • Chaos
  • Stars: Wolf-Rayet
  • Stars: massive
  • Techniques: photometric
  • Turbulence

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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