You can have even Weirder things happen in mass-exchange
Think about continuing evolution for case where most of the Star B
mass gets exchanged.
- Now have a Helium WD (B) plus a massive Main-sequence Star (A)
- When Star A begins its evolution up the RGB it will reach
its Roche Lobe radius and star to spill material back onto B (now
a He WD).
- As mass accumulates on the hot surface of the WD, it traps
radiation, heats up and when T reachs K the hydrogen begins
fusion to He and there is a dramatic flare-up in the luminosity
of the system.