[mesa-users] A common stellar-structure myth
Tuguldur Sukhbold
tuguldur.s at gmail.com
Tue Aug 30 22:03:00 EDT 2016
lower Z affects light and heavy stars a bit differently. For lighter stars
the opacity is smaller at low Z, and they burn slightly hotter and more
luminous (and quicker) - i.e. Alex's 1Msun is more luminous and lives
quicker than Richard's 1Msun.
For heavier stars there are the opposing effects of decreased n14 (catalyst
for cno), increased X (more fuel) and decreased mass loss - and the
resulting lifetimes and luminosities during the main sequence are not
terribly affected by low Z unless you go to really heavy stars.
As for the terminology, I agree with Richard. It was confusing to me when I
first found out that heavier stars have lower density.
Tuguldur
On Tue, Aug 30, 2016 at 8:36 PM, Craig Wheeler <wheel at astro.as.utexas.edu>
wrote:
> Alex's stars probably are dominated by electron scattering,
> at solar the opacity may be more Kramers...
>
> Craig
>
>
> On 8/30/16 7:20 PM, RICHARD H D TOWNSEND wrote:
> > Hi Alexander —
> >
> > Interesting! I wonder whether this is a result of degeneracy behaving
> differently in the Pop I vs Pop III cases. What initial metallicity did you
> assume — zero, or something small?
> >
> > cheers,
> >
> > Rich
> >
> >> On Aug 30, 2016, at 7:12 PM, Alexander Heger <
> alexander.heger at monash.edu> wrote:
> >>
> >> Dear Richard,
> >>
> >> I just looked at two stars, admittedly Pop III stars, and those, middle
> of H burn, pressure is 10x higher in 10 M_sun star compare to the 1 M_sun
> star. Both half way through H burn.
> >>
> >> Maybe an interesting difference to Pop I. And related to the shape of
> the curve in Ibeling & Duligur (2013).
> >>
> >> Never mind, gravitational acceleration is zero in the centre of both
> stars.
> >>
> >> -Alexander
> >>
> >> On 31 August 2016 at 09:56, RICHARD H D TOWNSEND <
> townsend at astro.wisc.edu> wrote:
> >> Hi Alex —
> >>
> >> In the context of an entry-level astronomy textbook, I think ‘gravity’
> is intended to reference acceleration (which students have every-day
> experience of) rather than potential (which they don’t).
> >>
> >> Regarding pressures — as you can see from the plot below, the pressure
> at the center of the massive star is about 0.5 dex smaller than that at the
> center of the solar-mass star. So, comparing pressures doesn’t help here.
> >>
> >> Rich
> >>
> >>
> >>
> >>
> >> --
> >> Sent from gmail.
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> --
> J. Craig Wheeler
> Samuel T. and Fern Yanagisawa Regents Professor of Astronomy
> President, American Astronomical Society, 2006-2008
> Department of Astronomy
> 2515 Speedway, Stop C1400
> Austin, TX 78712-1205
> 512-471-6407
> http://www.as.utexas.edu/~wheel
> http://ebooks.cambridge.org/ebook.jsf?bid=CBO9780511536625
> http://www.amazon.com/Krone-Ascending-ebook/dp/B00926QEGW
>
>
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