[Mesa-users] Fwd: other_momentum subroutine

[sheyda najafi]

Dear Francis

Thank you very much. I have attached the run_star_extras.f file. In the
other_momentum subroutine i have defined new variable named xn(i) which is
dependent on density in each zone therefore i assumed that it is defined at
cell center and added the extra force  (- beta* (clight**2)* (rho)*
(d(xn)/dm) ) as follows

-((   xn(k+1)-    xn(k)) / s% dm_bar(k)) * beta* (clight**2)* ( s% rho).

Also the inlist_project for pre MS and MS phases and inlist_load for the
RGB phase of 1 solar mass star ( without rotation) are attached.
 I am not sure whether i chose suitable values for the parameters in the
inlist_load or i must add some other information and change the values from
their defaults(controls_defaults).
 I would be grateful if you could help me.


Best Regards,



Sheyda Najafi

On Fri, Oct 20, 2017 at 6:39 PM, Francis Timmes <fxt44 at mac.com> wrote:

> one standard technique to investigate if an effect is numerical or perhaps
> physical
> is to conduct a convergence study with respect to mass resolution and time
> resolution.
> if the behavior changes significantly with improved mass and/or time
> resolution,
> then its probably numerical.
>
> you don't include your run_star_extras, so no one knows how you are coding
> other_momentum,
> but you should carefully study how mesa sets up its momentum equation,
> paying  attention
> to what quantities are defined at cell faces and which are defined at cell
> center.
>
> another suggestion, since your changing the momentum equation, is to
> explore the
> velocity and radial coordinate of your models to see if they make sense
> relative
> to the other assumption of your model (e.g., mass loss, etc).
>
> good luck!
>
> fxt
>
>
>
>
> > On Oct 20, 2017, at 4:07 AM, sheyda najafi via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
> >
> >
> > ---------- Forwarded message ----------
> > From: sheyda najafi <sh.najafi8590 at gmail.com>
> > Date: Fri, Oct 20, 2017 at 1:57 PM
> > Subject: other_momentum subroutine
> > To: mesa-users at lists.sourceforge.net
> >
> >
> > Hi MESA users
> >
> > I am trying to find the evolution of the RGB star in the presence of an
> extra force ((-Beta) * dx/dm), which is added to the other_momentum
> subroutine as follows
> >
> > dp/dm = - G m/4 pi r^4 - (Beta) * dx/dm
> >
> > where Beta is an arbitrary constant.
> >
> > I have run mesa for different Betas and as you can see in the attached
> plot (Tip of the RGB.png), the temperature of the Tip of the Red Giant
> Branch increases for (0<Beta<300) but for ( 300<Beta<400) there are some
> instabilities in the evolutionary track of the star and for (450<Beta<500)
> the instabilities increase in such a way that  the star leaves the standard
> track which is shown in the plot (HR.png) for Beta=450, and the code
> terminates therefore the evolution stops after RGB phase.
> >  Also for (Beta>500) the code does not converge even in zams phase.
> >
> > My question is whether we can have physical interpretation for the
> instabilities in the evolutionary track of the star or it is just the
> instability in the numerical code?
> >
> > In other words, is it admissible that the extra force becomes so large
> for beta>300, and makes the star unstable so the star can not live any
> longer and these models are not physical, or it is just a large quantity
> that makes the numerical code unstable?
> >
> > Thank you in advance
> >
> >
> >
> > Sheyda Najafi
> >
> >
> > <HR.png><Tip of the RGB.png>
>
>
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