Arm location pairs in polar coordinates. The error bars are the peak positions of spiral arms in the form of (θ, r) pairs in the deprojected version of Figure 1, where θ is the counter-clockwise deviation from the northeast semimajor axis. The colored lines are the best-fit companion-driven model to the observations. The angular offset between the colored lines is 1.°04 ± 0.°14. The observation does not follow the gravitational instability prediction for a 1.9 ± 0.2 M☉ central star.