The Per-Tau region in different tracers: (a): Planck’s E(B − V) dust (Abergel et al. 2014) and Dame et al. (2001)'s ¹²CO. 2D projections of the Per-Tau Shell and the Tau Ring models are shown. (b): HI4PI’s H I map (Bekhti et al. 2016). (c): Finkbeiner (2003)'s Hα map. (d): COMPTEL’s ²⁶Al map (1.8 MeV γ-ray; Diehl et al. 1995). (e)–(f): ROSAT’s X-ray 1/4. and 3/4 keV (Snowden et al. 1997; see also Figure 7 for eROSITA’s observations). The H I void and the X-ray emission blob (see also Appendix D) are indicated. The H I void, ²⁶Al, Hα, and X-ray observations suggest recent SN activity in the region (see Section 3.4.2).