Velocity artifacts created by a ring or horseshoe dust structure. Left panel: sketch representing the integrated gas emission over the line width as a function of the disk radius. The black solid line is the gas emission without the dust ring, and the two red lines represent the emission in presence of the dust ring before and after continuum subtraction. The two ellipses indicate the position of two synthesized beams. Right panel: line emission profile (black solid line) in the simplified case where the line emission is the sum of the emission at the inner (blue dashed line) and outer (red dashed lines) edges of the synthesized beam. The velocity v_c, represented by the dotted black vertical line, is the velocity at the center of the beam while v_m, represented by the solid black line, is the intensity weighted velocity.