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Known also as S Dor stars. Exhibit slow changes in brightness with occasional outbursts of substantial mass loss. Very heavy stars(>30Msun), often in binary systems, will evolve to W-R stars. Only a few is known. Known example: Eta Carinae.

Eta Carinae, ESO

M_V \sim -11 \ldots -8 mag

  • Baseline micro-variability: P around 10-20 days, amplitude 0.1-0.2 mag
  • Positioned close to "instability strip", thus the pulsating-like variability
  • "normal eruptions": 1-2 mag (rise within few months), repeating with period of years or decades the brighter abs.mag the shorter period between eruptions)
  • Giant eruptions ("Eta Carinae type") of around 8 mag, once a few centuries!!
  • After giant eruption and fade, the star recovers its brightness as the dust disperses.
  • Spectroscopic variations with period of 5.5 years (probably due to binarity)
  • X-ray variability
  • engine of outbursts is not well understood yet
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