A Radio Pinwheel Emanating from WR147
  Wolf-Rayet (WR) stars are evolved massive stars, presumably on their way to
becoming supernova. They are characterized by high luminosities and fast and
dense stellar winds. We have detected signs of a radio continuum pinwheel
associated with WR147, a nitrogen-rich WR star with spectral subtype WN8. These
structures are known around a handful of late-type carbon-rich WR stars with
massive companions were the dust formed at the zone where the two winds collide
produces a plume of dense gas and dust that is carried out with the WR wind. As
the binary system rotates, an Archimedean spiral detectable in the infrared is
formed. The resulting pinwheel contains information on wind speeds,
wind-momentum ratio and orbital parameters. However, WR147 is a WN star and the
formation of dust is unlikely so a different emission mechanism must be at
work. Our analysis of the data suggests that in this case the emission is
dominantly of non-thermal nature (synchrotron), although we cannot exclude that
some clumps could be brighter in free-free emission. It is possible that the
pinwheels associated with WN stars will be detectable only as non-thermal
emitters at radio wavelengths. From the characteristics of the pinwheel we
estimate a period of 1.7 years for the binary system (the WN8 star and a
companion yet undetected directly) responsible for the pinwheel.
