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[vsnet-alert 7546] WR 104: sudden fading!

WR 104: sudden fading!

  WR 104 = HadV82 (WR+OB, pinwheel nebula) is experiencing shown another
remarkable fading episode!

  YYYYMMDD(UT)   mag  observer
  20020720.514  10.18Ic  (Seiichiro Kiyota)
  20020720.515  12.56V  (Seiichiro Kiyota)
  20020809.538  123p  (Katsumi Haseda)
  20020810.539   123  (Hiroshi Itoh)
  20020813.540  122p  (Katsumi Haseda)
  20020828.528  123p  (Katsumi Haseda)
  20020829.535  10.33Ic  (Seiichiro Kiyota)
  20020829.542  12.57V  (Seiichiro Kiyota)
  20020831.517   126  (Hiroshi Itoh)
  20020919.460  10.88Ic  (Seiichiro Kiyota)
  20020919.469  13.50V  (Seiichiro Kiyota)
  20020924.494  11.53Ic  (Seiichiro Kiyota)

[From the abstract of Kato et al. (2002) PASJ 54, 51L "Discovery of Extremely
Large-Amplitude Quasi-Periodic Photometric Variability in a WC9-Type
Wolf-Rayet Binary, WR 104]

  We discovered that the Wolf--Rayet (WR)+OB star binary WR 104,
renowned for its associated "dusty pinwheel nebula", recently spatially
resolved with infrared interferometry, exhibits strong quasi-periodic
optical variations with a full amplitude of 2.7 mag.
Such a large-amplitude, continuous variation has been unprecedented
in a WR star.  The optical quasi-period (~241 d) is
in almost perfect agreement with the interferometric period (243.5+/-3 d).
The remarkable agreement of the dominant period in optical variability
with the orbital period supports that the strongly varying dust obscuration
is physically related to the binary motion, rather than sporadic
dust-forming episodes.  Considering the low orbital inclination
(11+/-7 deg) and the nearly circular orbit inferred from the
interferometric observations, the strongly variable line-of-sight extinction
suggests that the highly structured extinction might be in the process of
being formed via the ejection of dust in the direction of the binary
rotation axis.
Another viable explanation is that the three-dimensional structure of
the shock front, itself, is the obscuring body.
Depending on the geometry, the dusty shock front near the conjunction
phase of the binary can completely obscure the inner WR-star wind and
the OB star, which can explain the amplitude of the optical fading
and the past observation of remarkable spectral variation.

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