tokens: at ∼0.1 arcsec, as illustrated in Fig. 14(d) . Below R ∼ 0.05 arcsec, the effect of absorption becomes very important and complicates the picture, however with no significant impact on the present argument. We checked that this result remains true when considering only one quadrant (north-west, south-west, north-east, or south-east; see Fig. A2 of the appendix) of the sky plane. A natural interpretation of these results is to make the line width, rather than the wind velocity, responsible for the production of large Doppler velocity wings. As thermal broadening cannot produce such large line widths, turbulence must be invoked. The picture would then be of a shell surrounding the zone where stellar pulsation dominates and extending up to ∼10 au, hosting a very turbulent regime. Indeed, such a possibility was mentioned earlier by Kamínski et al. ( 2016 ) in relation with the possible presence of very broad AlO line profiles. According to the standard picture of acceleration by transfer of momentum from dust grains to molecules of gas (Höfner Olofsson 2018 ), this is a region that hosts important shocks. At 10 au, the escape velocity from one (two) solar masses, values commonly accepted for Mira A, is ∼13 (19) km s −1 and the density is such that the velocity acquired by a gas molecule after its interaction with a dust grain is immediately thermalized. Such important turbulence has been observed in a different context by Falgarone Phillips ( 1990 ) and discussed by Gillet et al. ( 1998 ) in the case of pulsating stars. If such a scenario were confirmed, it would require revisiting in its context the cases of the other mentioned AGB stars, L 2 Pup, EP Aqr, and R Dor, which is, however, beyond the scope of this work. In the same spirit of seeking a description of high Doppler velocity wings in terms others than a simple acceleration of the wind, Homan et al. ( 2018a ) have suggested a possible contribution of inelastic collisions in a mixed granular particle fluid. They were first, to our knowledge, to underline explicitly the need for a reliable description of such high-velocity wings and for an explanation of their relative importance in SiO emission with respect to CO emission Finally, we note that the models used by Wong et al. ( 2016 ) and Khouri et al. ( 2018 ) fail to reproduce the large Doppler velocities displayed in Fig. 14 . Indeed, these models do not account for important turbulence. If important turbulence is present between 5 and 10 au from the star, causing a broadening of the SiO line profile at the level of 20 km s −1 full width, this raises the question of the validity of models that ignore it at shorter distances and may significantly impact the conclusions reached by Wong et al. ( 2016 ) and Khouri et al. ( 2018 ) in the close neighbourhood of the star. 9 SUMMARY AND CONCLUSIONS The above study of the morpho-kinematics of the circumbinary envelope of the Mira AB pair at distances between ∼100 and ∼350 au from the stars
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