tokens: the outer and inner edges of the synthesized beams. When this ratio is greater than 1, the measured velocity becomes sub-Keplerian, and vice versa. Starting from the initial non-convolved image, this ratio can be perfectly known in the models and is shown in the bottom-center and bottom-right panels of Fig. 6 . As expected, the emission ratio I out ∕ I in is larger at 0.3′′ than at 0.1′′ and lead to stronger velocity biases. In real observations, the emission ratio can only be approached because the image received is already convolved by the observational beam. We show, however, in the bottom-left panel of Fig. 6 that the general tendency of the flux variations can be recovered, even if their magnitude is probably underestimated. In general, we find in our models that the flux ratio I out ∕ I in is proportional to the beam size, with ratios at 0.3′′ about three times larger than at 0.1′′, which is an expected result when the spatial variation of the line emission is relatively smooth compared to the synthesized beam size. Furthermore, biases are also sensitive to the velocity range Δ V probed by the synthesized beam, which is proportional to the beam size, and increases at smaller distances from the star dueto the steeper gradient of the Keplerian velocity. This leads to velocity artifacts generally larger at 0.3′′ compared to 0.1′′ and particularly important in the inner regions of the disk. Along the northern major axis, as shown in the top panel of Fig. 7 , the velocity deviations at 0.1′′ are about three times smaller thanat 0.3′′. Going to a higher spatial resolution will have then the double advantage of (i) reducing velocity biases and of (ii) allowing a better determination of the value and morphology of these biases, through a more precise knowledge of the disk structure. 4.3 Dust also affects the measured gas velocity The circumbinary disk around HD 142527 is not only made of gas but also contains a large concentration of dust particles at the north of the disk. The presence of this dust concentration, which is optically thick at 0.9 mm with τ Dust ~ 2–3 ( Muto et al. 2015 ; Boehler et al. 2017 ), has an important impact on the measured gas velocity at the north of the disk, as shown in the top panel of Fig. 7 . The four radial regions indicated in this figure are delimited by the radii at which the velocity shifts between a sub- and a super-Keplerian velocity at the spatial resolution of 0.3′′. Regions I and IV, which contain almost no millimeter dust emission, correspond to the two regions described previously in Sect. 4.2 . The 13 CO integrated emission uniformly increases for R ≤ 135 au and decreases for R ≥ 270 au, leading to the sub-Keplerian and to the super-Keplerian profiles. Fig. 7 Velocity deviations due to the presence of dust along the north of the major axis. Top : velocity deviations measured in the pure Keplerian model at two different spatial resolutions. Middle : 13 CO integrated emission and dust emission in
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