Simulated images of WH with different V₀. We assumed that dust ejection happened for one day impulsively around 29.5 days before the observation. The field-of-view of each image is identical to the one of Fig. 1b. The comet-like ejection velocity, $V(a)=V_0\times \sqrt{\beta }$, was used for this model. We assumed hemispherical dust ejection with fixed β range (3 × 10⁻⁴ ≤ β ≤ 1 × 10⁻²) and q for the differential size distribution.