red-giant and post red-giant evolution  stars

Minitial/Msun <
0.2 - 0.7 ??

Minitial/Msun    <   5 - 8

Mcore/Msun  < 2

Minitial/Msun    >  8

Mcore/Msun  > 2

complete electron degeneracy 
sets in before 
3He → C starts:

the star is dead

partial electron degeneracy
 sets in as 3He → C begins

no electron degeneracy

(these stars begin life much less dense than the low-mass stars, so that contraction during the main-sequence phase does not cause them to get near electron degeneracy)

P = (PHe) + P P = Kne5/3  + (negligible nHekT) P =  ( nHe + ne )kT 
no He Burning positive feedback:
energy released in
3He → C goes into increased reaction rate which leads to explosive He core flash (L ~ L galaxy) muffled by the envelope...

energy released:
1) removes electron degeneracy
expands the core (i.e., goes into gravitational energy) 
3) produces shock waves that drive envelope away
(origin of the planetary nebula)

negative feedback:
energy released in 3He → C   goes into KE which raises the pressure, thereby expanding and cooling the core...

this results in a stable He burning core

no He Burning 3He → C fusion temporarily ceases

infall of outer layers reverses
explosion of inner core and
entire star contracts, thereby
re-heating core and layers until

3He → C begins stably in core

start-and-stop H → He begins again in shell (bursts of luminosity; thermal pulses) produce shock waves that continue to drive envelope away

3He → C begins peacefully and stably

eventually core He runs out

the C core must contract
to maintain thermal pressure 
(thermal energy continues to flow to surface)

before C burning can start, complete
electron degeneracy sets in

the star is dead

it radiates the kinetic energy of the (boson) nuclei, and it dims and cools as the KE is used up

eventually core He runs out

C core contracts, heats up, until C burning begins peacefully and stably;
the star lives on through another round of fusion

each time a fuel runs out, this process continues in the core, until Fe/Ni (endothermic) fusion,

which leads to the supernova's implosion