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 ( \sim 241 d ) is in almost perfect agreement with the interferometric period ( 243.5 \pm 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 \pm 7 ^ { \circ } ) and the nearly circular orbit inferred from the interferometric observations , the strongly variable line-of-sight extinction suggests that the highly structured extinction can be being formed via an 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 optical fading and the past observation of remarkable spectral variation .