SN 2022joj optical and UV photometry follow-up

We show that these unusual spectroscopic properties are broadly consistent with the helium-shell double detonation of a sub-Chandrasekhar mass (M~1M_{sun}_) carbon/oxygen white dwarf from a relatively massive helium shell (Ms~0.04-0.1M_{sun}_), if observed along a line of sight roughly opposite to where the shell initially detonates. None of the existing models could quantitatively explain all the peculiarities observed in SN 2022joj.

The low flux ratio of [NiII]{lambda}7378 to [FeII]{lambda}7155 emission in the late-time nebular spectra indicates a low yield of stable Ni isotopes, favoring a sub-Chandrasekhar mass progenitor. The significant blueshift measured in the [FeII]{lambda}7155 line is also consistent with an asymmetric chemical distribution in the ejecta, as is predicted in double-detonation models.