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

http://news.nationalgeographic.com/n...onomy-science/

The study could upend current theories about how some stars that are
similar to our sun die and become the basic building blocks for the
next generation of stars and planets.

According to existing stellar evolution models, sunlike stars—those
that are similar in size and chemical composition to our sun—swell to
become so-called red giants in their final stage of life, before
losing their atmospheres in a spectacular bubble of gas and dust.

But now astronomers have found that not all sunlike stars follow the
same rules when it comes to the end of their life cycles, and that
some can skip the AGB phase altogether.

By tracking the sodium levels, the researchers were able to identify
which stars would undergo the AGB phase at the end of their lives.

On 5/30/13 8:19 AM, Yousuf Khan wrote:
http://news.nationalgeographic.com/n...onomy-science/


The study could upend current theories about how some stars that are
similar to our sun die and become the basic building blocks for the
next generation of stars and planets.

According to existing stellar evolution models, sunlike stars—those
that are similar in size and chemical composition to our sun—swell to
become so-called red giants in their final stage of life, before
losing their atmospheres in a spectacular bubble of gas and dust.

But now astronomers have found that not all sunlike stars follow the
same rules when it comes to the end of their life cycles, and that
some can skip the AGB phase altogether.

By tracking the sodium levels, the researchers were able to identify
which stars would undergo the AGB phase at the end of their lives.


Cool.

On 30/05/2013 9:45 AM, Sam Wormley wrote:
On 5/30/13 8:19 AM, Yousuf Khan wrote:
By tracking the sodium levels, the researchers were able to identify
which stars would undergo the AGB phase at the end of their lives.


Cool.

Of course, what's not mentioned in the report is, if the stars don't go
AGB, then what do they do, when it's time to die? What happens to their
outer envelops?

Yousuf Khan

In article ,
Yousuf Khan writes:
http://news.nationalgeographic.com/n...onomy-science/

The link above has a link to a preprint of the paper.

According to existing stellar evolution models, sunlike stars—those
that are similar in size and chemical composition to our sun—swell to
become so-called red giants in their final stage of life, before
losing their atmospheres in a spectacular bubble of gas and dust.

But now astronomers have found that not all sunlike stars follow the
same rules when it comes to the end of their life cycles, and that
some can skip the AGB phase altogether.

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.

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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