2025RNAAS...9..297B

I report the discovery of a previously uncatalogued emission nebula surrounding the B-type star HD 213231 in the constellation Cepheus. The object is centered at ${\alpha }_{{\rm{J2000}}}=2{2}^{{\rm{h}}}2{8}^{{\rm{m}}}30\mathop{.}\limits^{\rm{s}}57$, ${\delta }_{{\rm{J2000}}}=+5{8}^{\circ }5{0}^{{\prime} }52\mathop{.}\limits^{{\prime\prime} }78$ and exhibits strong Hα and [S II] emission with faint traces of [O III]. The initial indication of nebulosity appeared in a 114 hr narrowband SHO image of the Sh2-135 region obtained in summer 2025 using a Sky-Watcher Esprit 100ED telescope with a ZWO ASI2600MM Pro camera and Antlia 2.5 nm filters. Follow-up imaging with a Celestron 9.25” EdgeHD telescope (0.7× reducer) confirmed the presence of a compact, ionized structure through 44 hr of integration (Hα 10 hr, [S II] 24 hr, [O III] 10 hr). The nebula's morphology and high Hα/[O III] ratio are consistent with a small H II region likely ionized by the nearby B-type star. Faint diffuse emission at the same location is visible in the Digitized Sky Survey (DSS color) via Aladin Lite, supporting the conclusion that this is a genuine, previously unrecognized emission nebula.