[Mesa-users] Energy conservation on the main sequence

[Pablo Marchant]

Yes, I did this a while back and you need to account for the change in rest
mass energy. Essentially you can get ~6.7e18 ergs per gram of burnt
hydrogen. During the main sequence you're tapping into this rest mass
energy, so if you don't include it explicitly you won't get energy balance
right.

Playing with this I'm simply defining

E = internal_energy + gravitation_binding_energy + M*X*6.7e18

and defining the energy lost from the system as

L_lost = L_surf + L_neu

doing this in a MESA run I just checked that I get similar values for dE/dt
(computed by comparing the value from step to step) and L_lost.

Cheers

On Sun, Feb 17, 2019 at 3:11 PM RICHARD H D TOWNSEND <
townsend at astro.wisc.edu> wrote:

> 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
> > https://lists.mesastar.org/mailman/listinfo/mesa-users
> >
> >
> >
> > --
> > Pablo Marchant Campos
> > M.Sc on Astrophysics, Universidad Católica de Chile
> > PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
>
>

-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
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