None of them appeared in elliptical galaxies, which are filled with old stars. This suggests that Type Iax supernovas come from young star systems.
Somebody help me out here. Wouldn’t a carbon/oxygen white dwarf star be a second generation star? Are second generation stars consistent with young systems?
I believe you are right. If I understand things correctly, elements of the periodic table, up to and including carbon, can be created in stars. No problem. Elements heavier than that, of which oxygen is one, can only be created in a supernova. But as you seem to suspect, a “young” system need not be a first generation system; i.e., ‘young’ in this context only means the star in question formed recently. The cloud of gas and dust, out of which it formed, may have contained heavy elements that were thrown out by an older supernova.
Not sure, but I think it’s possible for a star to start fusing helium into carbon & oxygen when it runs out of hydrogen.