Not all Sun-like stars will become red giants, sodium levels to blame

On 06/06/2013 5:37 PM, Steve Willner wrote:
The above press release text is literally correct but could be
misleading because of the abrupt switch from "red giant" (RG) to
"asymptotic giant branch" (AGB). The RG phase is an early stage of
post-main-sequence evolution where the star is "burning" hydrogen in
a shell (the core having been depleted of hydrogen). The AGB phase
is a later, much briefer phase where the core is also depleted of
helium, and the star is burning hydrogen in an outer shell and helium
in an inner shell.

What the new work shows is that some stars -- more precisely some
stellar populations -- skip the AGB phase. The reason is unknown,
but it may have to do with helium abundance or details of mass loss
in the RG phase. All stars (in the relevant mass range) go through
the RG phase; they don't evolve directly from the main sequence to
white dwarf, despite what the press release might suggest.

Well, that makes some sense. If a star doesn't expel its outer layers
then how in the world would it become a naked white dwarf?

Yousuf Khan