Case B mass transfer

Case B mass transfer starts after core hydrogen exhaustion and before core helium ignition. It is subdivided by donor structure; early case B mass transfer occurs before a deep convective giant envelope develops.

Early case B overflow occurs in an early post-main-sequence donor, commonly crossing the Hertzsprung gap with a largely radiative envelope. A stabilizing mass-loss response can allow transfer at binary mass ratios that would destabilize a convective giant. This is an evolutionary-stage classification, distinct from recombination terminology.