[mesa-users] initial entropy of low-mass stars & planets

[Francis Timmes]

entropy is a thermodynamic quantity that, in general, is set
by the equation of state through specification of the local
temperature, density, and composition. as such, and again
in general, there is no single closed form equation for the entropy.

“avo” stands for the avogadro number N_A. 
the specific entropy has units of erg/g/K, so dividing 
by N_A * k_B makes the specific entropy dimensionless. 
similar in spirit to writing boltzmann’s equation as S/k_B = log W
where W is the number of equally probably microstates. 

fxt



> On Nov 13, 2014, at 9:25 AM, Ryan Cloutier <cloutier at astro.utoronto.ca> wrote:
> 
> Hi all.
> 
> I've been attempting to vary the initial entropy of a suite of low-mass
> stars and planets by hand. Since there does not exist a single entropy
> parameter that can be varied, I've been playing with the models' physical
> properties such as initial radius, initial mass, initial core temperature,
> etc. I'm wondering if anyone knows exactly how entropy is prescribed. In
> these fully convective models the entropy profile is (mostly) constant but
> I would still like to know the equation used by MESA to compute that
> initial entropy value. That is, what other variables does the entropy
> profile depend on? Any insight would be greatly appreciated.
> 
> As an aside in profile_columns.list the (linear) specific entropy profile
> is said to be divided by avo*kerg, where the quantity avo doesn't appear
> to be defined anywhere. Does anyone know what avo is? Obviously this is
> important for analysis with units that are understood.
> 
> If it matters I'm using using MESA version 6794.
> 
> Thanks a lot!
> 
> -Ryan
> 
> 
> -- 
> Ryan Cloutier
> Dept. of Astronomy and Astrophysics
> University of Toronto
> 
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