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) + Pe | 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 2) 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 before C burning can start, complete
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;
|