Spatio-kinematic properties of the SS-outflow of OH 231.8 deduced from the SiS υ = 0, J = 12–11 ALMA maps. Left: schematic geometry and velocity field (arrows) of the compact SS-outflow. This plot represents a slice of the SS-outflow through a plane perpendicular to the plane of the sky oriented along PA = 25°. In this figure, 0.1 corresponds to 150au and the largest arrows correspond to V_exp = 16km s⁻¹. Right: position-velocity (PV) diagram of the SiS υ = 0, J = 12–11 data with 60 mas-resolution along the direction of the nebula axis (PA ~ 25° ) through the nebula center (δx = 0″) and synthetic axial-PV diagram (white line) resulting from the model in the left. The values of the projected velocity gradients, ∇v₁ and ∇v₂, measured along the rear (front) side of the northern (southern) lobe and the rear (front) side of the southern (northern) lobe, respectively, are indicated as dashed lines.