Illustration of dust capture in the settling regime. Planetesimals with a radius R_p between about 100 km and 1000 km have a Bondi radius larger than R_p but smaller than the Hill radius (see text). For the critical stopping time corresponding to a stopping time equal to the time necessary for the unperturbed dust particle to cross the Bondi sphere, the effective cross section for capture is b_set ~ R_B. The approximate trajectory of the dust for is indicated by red lines. For smaller dust particles with (dashed green lines), the deflection by the gravitational pull of the planetesimal is smaller, hence a smaller effective capture radius.