How are Type II, Ib, or Ic supernovae classified?

Answer

By whether the star retained its outer hydrogen and helium layers before exploding.

The specific classification among Type II, Ib, or Ic depends on the remnants of the star's outer layers—specifically, whether the star still possessed its outer hydrogen and helium layers when the core-collapse explosion occurred.

How are Type II, Ib, or Ic supernovae classified?
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