Left: surface density of the accretion disk at t = 8000 yr after the launch of the intruder, just before the onset of fragmentation in the ejected spiral arm (shown by the green arrow). Only the region inside 1000 AU from the central star is shown. The green dashed lines mark the position of the intruder star. Middle: red contour lines show the regions with the Toomre Q-parameter smaller than unity, while the gray-shaded area indicated the disk regions where the Gammie -parameter is smaller than three. Right: ratio N_Jeans of the Jeans length to the minimum of the local grid cell size in both coordinate directions (r,φ), in log scale. The minimum value of N_Jeans in the ejected arm is about two and it increases to between three and five in some parts of the arm, meaning that the Truelove criterion may not be resolved in the entire spiral arm.