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neilzero
2011-Feb-03, 11:03 PM
Does complete convection occur in stars less than 0.4 solar mass and not occur in stars over 0.8 solar mass? I presume there is a zone where either can happen. It seems to me that high metallicity in the star would reduce the probability of convection except early in life and that high metallicity might prevent stars with less than 0.4 solar mass from fusing hydrogen in the core and prevent thermal convection after most of the elements heavier than hydrogen have settled to the core. Is present metallicity for stars about 5%? As you can tell I prefer numbers to generalities. The first two posts of the thread that inspired these questions (Q&A forum) are:
Titanium48
Frozen stars
In their "fate of the universe" paper (Reviews of Modern Physics, Vol. 69, No. 2, April 1997), Adams and Laughlin discuss the effects of increasing metallicity star formation, speculating that increasing metallicity will eventually reduce the minimum mass to initiate hydrogen burning to about 4% of the mass of the sun, and that these stars would be so well insulated that water could condense in their atmospheres while fusion slowly proceeded in their cores. Do we know how much additional heavy elements this would require? Is it possible that any of these objects have already formed in locations unusually enriched in heavy elements or by a mechanism that provided heavy element enrichment?
neilzero
It appears that metallicity is increasing in the visible portion of the Universe. I suppose in the very far future, some one sol mass star will be less than 50% hydrogen, but why would we suppose that the core would be 50% or even 10% hydrogen in a star that just began main sequence? Can fusion begin in a core that is only 10% hydrogen? Would the hydrogen not leave the core and collect near the surface, as the heavier elements sank into the core? Neil

Hornblower
2011-Feb-03, 11:33 PM
Does complete convection occur in stars less than 0.4 solar mass and not occur in stars over 0.8 solar mass? I presume there is a zone where either can happen. It seems to me that high metallicity in the star would reduce the probability of convection except early in life and that high metallicity might prevent stars with less than 0.4 solar mass from fusing hydrogen in the core and prevent thermal convection after most of the elements heavier than hydrogen have settled to the core. Is present metallicity for stars about 5%? As you can tell I prefer numbers to generalities. The first two posts of the thread that inspired these questions (Q&A forum) are:
Titanium48
Frozen stars
In their "fate of the universe" paper (Reviews of Modern Physics, Vol. 69, No. 2, April 1997), Adams and Laughlin discuss the effects of increasing metallicity star formation, speculating that increasing metallicity will eventually reduce the minimum mass to initiate hydrogen burning to about 4% of the mass of the sun, and that these stars would be so well insulated that water could condense in their atmospheres while fusion slowly proceeded in their cores. Do we know how much additional heavy elements this would require? Is it possible that any of these objects have already formed in locations unusually enriched in heavy elements or by a mechanism that provided heavy element enrichment?
neilzero
It appears that metallicity is increasing in the visible portion of the Universe. I suppose in the very far future, some one sol mass star will be less than 50% hydrogen, but why would we suppose that the core would be 50% or even 10% hydrogen in a star that just began main sequence? Can fusion begin in a core that is only 10% hydrogen? Would the hydrogen not leave the core and collect near the surface, as the heavier elements sank into the core? Neil

Why do you think increased metallicity would reduce convection?

John Jaksich
2011-Feb-15, 05:50 AM
Hello Neil,

For the least massive stars----M < .26 solar masses---- are convective throughout
For intermediate mass stars--- .26 solar masses to 1.5 solar masses-----the core is radiative and the "envelope is convectve"

For massive stars------greater than 1.5 solar masses-----the core is convective and the envelope is radiative---



It may stand to reason that the larger stars are "normally" older and are less metallic

The other two possess a higher metallicity by virtue of the fact that they are produced by the remnants of past supernova & possible hyper-nova of extremely old & massive stars.


There is obviously more to add----but I will try to get back to you later . . .




Does complete convection occur in stars less than 0.4 solar mass and not occur in stars over 0.8 solar mass? I presume there is a zone where either can happen. It seems to me that high metallicity in the star would reduce the probability of convection except early in life and that high metallicity might prevent stars with less than 0.4 solar mass from fusing hydrogen in the core and prevent thermal convection after most of the elements heavier than hydrogen have settled to the core. Is present metallicity for stars about 5%? As you can tell I prefer numbers to generalities. The first two posts of the thread that inspired these questions (Q&A forum) are:
Titanium48
Frozen stars
In their "fate of the universe" paper (Reviews of Modern Physics, Vol. 69, No. 2, April 1997), Adams and Laughlin discuss the effects of increasing metallicity star formation, speculating that increasing metallicity will eventually reduce the minimum mass to initiate hydrogen burning to about 4% of the mass of the sun, and that these stars would be so well insulated that water could condense in their atmospheres while fusion slowly proceeded in their cores. Do we know how much additional heavy elements this would require? Is it possible that any of these objects have already formed in locations unusually enriched in heavy elements or by a mechanism that provided heavy element enrichment?
neilzero
It appears that metallicity is increasing in the visible portion of the Universe. I suppose in the very far future, some one sol mass star will be less than 50% hydrogen, but why would we suppose that the core would be 50% or even 10% hydrogen in a star that just began main sequence? Can fusion begin in a core that is only 10% hydrogen? Would the hydrogen not leave the core and collect near the surface, as the heavier elements sank into the core? Neil