[Mesa-users] Energy conservation on the main sequence

RICHARD H D TOWNSEND townsend at astro.wisc.edu
Sun Feb 17 16:11:57 EST 2019


I think L_neu has no effect on the energy budget because L_neu(surface) = L_neu(core).

So, total change in energy = (L_nuc + L_neu - L - L_neu)*dt = (L_nuc - L)*dt

However, could the discrepancy be due to changes in the stellar rest-mass energy?

cheers,

Rich

On Feb 17, 2019, at 2:24 PM, Pablo Marchant <pamarca at gmail.com> wrote:
> 
> Things do seem to match at the beginning, which I assume is the pre-MS. So I'm guessing you're missing something related to nuclear reactions. Maybe L_neu?
> 
> Easier to check with inlists at hand for sure.
> 
> Cheers
> 
> On Sun, Feb 17, 2019 at 2:21 PM Bill Paxton <paxton at kitp.ucsb.edu> wrote:
> Hi Rich,
> 
> Please provide inlists etc so we can play along with you, starting by being able to reproduce your plots.
> 
> Thanks,
> Bill
> 
> > On Feb 17, 2019, at 12:14 PM, RICHARD H D TOWNSEND via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> > 
> > Hi folks --
> > 
> > I'm writing to ask about energy conservation on the main sequence, for a solar-mass star. I'm not yet sure whether this is more of a question about stellar evolution, or about MESA.
> > 
> > In the attached figure, I plot two quantities as a function of time:
> > 
> > tot_E_change -- the total energy change across each timestep
> > total_energy_sources_and_sinks -- the total energy sources/sinks across each timestep
> > 
> > For this evolutionary stage, total_energy_sources_and_sinks is practically identical to (L_nuc - L)*dt, where L_nuc is the nuclear luminosity, L the surface luminosity, and dt the timestep.
> > 
> > My understanding is that the two quantities should align perfectly -- the net energy gain/loss is matched by a change in the star's total energy (which, according to the virial theorem, will result in an expansion/contraction). But that's clearly not what we see; while total_energy_sources_and_sinks is always positive (with the exception  of the ZAMS), the tot_E_change is initially negative and only becomes positive later on in the evolution.
> > 
> > I'm clearly missing something important, but I'm not sure what. So, can anyone help clarify what's going on?
> > 
> > cheers,
> > 
> > Rich
> > 
> > <energe-change.pdf>_______________________________________________
> > mesa-users at lists.mesastar.org
> > https://lists.mesastar.org/mailman/listinfo/mesa-users
> > 
> 
> _______________________________________________
> mesa-users at lists.mesastar.org
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> 
> 
> 
> -- 
> Pablo Marchant Campos
> M.Sc on Astrophysics, Universidad Católica de Chile
> PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn



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