2025ApJ...994...23S

Thermonuclear supernovae (SNe) are the result of the nuclear transformation of carbon/oxygen white dwarfs (WDs) to the radioactive element ⁵⁶Ni and intermediate mass elements like Ca, Ar, etc. Most progenitor scenarios involve a companion star that donates matter to the exploding WD, implying a fundamental prediction: the formation of a wake in the explosive ejecta as it runs into and moves past the companion star. This wake leaves an indelible imprint on the ejecta's density, velocity, and composition structure that remains fixed as the ejecta reaches homologous expansion. We simulate the interaction of the ejecta and Roche-lobe filling donor in a double degenerate double detonation Type Ia progenitor scenario and explore the detectability of this imprint in late-time nebular phase spectroscopy of Type Ia SNe under the assumption of local heating (t > 200 days). At these times, the velocity profiles of forbidden emission lines reflect the velocity distribution of all of the ejecta and the critical electron density for that forbidden line. We explicitly calculate line shapes for the [Co III] 11.89 μm line that traces the initial ⁵⁶Ni distribution and the [Ar III] 8.99μm line, which traces a typical intermediate mass element. We predict the viewing angle dependence of the line shape, present a tool to quickly calculate optically thin line shapes for various 3D density-velocity profiles, and discuss JWST observations.