(a) Angular distance of OB stars around S205 from its geometric center as a function of trace-back time. The gray shaded area corresponds to locations inside the S205 boundary. The trace-back curve of HD 22253 is highlighted, with the time of closest approach (6.5 Myr ago) indicated. (b) Trace-back trajectory of HD 22253 relative to the S205 center (blue dashed line), with the hollow star symbol marking its position 6.5 Myr ago. See Section 5.2.