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Models for supernovae (SNe) arising from thermonuclear explosions of whitedwarfs (WDs) have been extensively studied over the last few decades, mostlyfocusing on the single degenerate (accretion of material of a WD) and doubledegenerate (WD-WD merger) scenarios. In recent years it was suggested thatWD-WD direct collisions provide an additional channel for such explosions. Herewe extend the studies of such explosions, and explore the role of Helium-shellsin affecting the thermonuclear explosions. We study both the impact of low-masshelium ($\sim0.01$ M$_{\odot})$ shells, as well as high mass shells ($\ge0.1$M$_{\odot}$). We find that detonation of the massive helium layers precede thedetonation of the WD Carbon-Oxygen (CO) bulk during the collision and canchange the explosive evolution and outcomes for the cases of high massHe-shells. In particular, the He-shell detonation propagates on the WD surfaceand inefficiently burns material prior to the CO detonation that later followsin the central parts of the WD. Such evolution leads to larger production ofintermediate elements, producing large yields of $^{44}{\rm Ti}$ and $^{48}{\rmCr}$ relative to the pure CO-CO WD collisions. Collisions of WDs with alow-mass He-shell do not give rise to helium detonation, but helium burningdoes precede the CO bulk detonation. Such collisions produce a high velocity,low-mass of ejected burned material enriched with intermediate elements, withsmaller changes to the overall explosion outcomes. The various effects arisingfrom the contribution of low/high mass He layers change the kinematics and themorphological structure of collision-induced SNe and may thereby provide uniqueobservational signatures for such SNe, and play a role in the chemicalenrichment of galaxies and the production of intermediate elements andpositrons from their longer-term decay.

Supernovae from direct collisions of white dwarfs and the role of helium shell ignition