[Mesa-users] Finding ZAMS

Fri Mar 15 13:23:49 EDT 2019

Hi Thomas,

OK, now I understand!  Thanks.

I still maintain that the ZAMS is hard to define precisely, especially in
terms of L_nuc/L or L_H/L, and so I would suggest something that is both
easy and straightforward to define and measure in your models.

I have found that the minimum radius--or maximum log(g), signalling the end
of pre-main sequence contraction, is a useful proxy that is also easy to
locate.  You can use the same test on center H1 that I suggested yesterday
to define the domain over which you search for min(r) or max(log(g)).

Aaron

On Fri, Mar 15, 2019 at 1:03 PM Thomas Steindl <
Thomas.Steindl at student.uibk.ac.at> wrote:

> Hi Aaron,
>
> I am sorry, I forgot that. I am trying to investigate the probing
> power of g-modes on the pre-MS and I would like to compare models that
> have the same percental age in respect to the model's age at ZAMS (
> age(model)/(age(ZAMS_model) ). Without a proper definition of ZAMS I
> am not able to be certain I am comparing the 'matching models'.
>
> Thomas
>
> Zitat von Aaron Dotter <aaron.dotter at gmail.com>:
>
> > Hi Thomas,
> >
> > In order for us to advise you, it would be helpful for you to answer my
> > first question:
> >
> > "The ZAMS is a hard thing to define precisely.  What does it mean for the
> > project you're working on?"
> >
> > Why do you need a precise ZAMS definition?  I think you're finding, as
> > others have before, that it is not something that is easily and
> succinctly
> > defined for the full range of stellar masses.
> >
> > Cheers,
> > Aaron
> >
> > On Fri, Mar 15, 2019 at 12:24 PM Thomas Steindl <
> > Thomas.Steindl at student.uibk.ac.at> wrote:
> >
> >> Hello,
> >>
> >> I have now tried your stopping condition. Therefore, I calculated 21
> >> models in a mass range of 0.5 to 6 solar masses (the 0.775 M_sun
> >> modelled would not converge). The stopping condition works well for
> >> the masses 1.05 - 5ish solar masses depending on where you define the
> >> cut off criterion. For the models with higher masses the ratio L_H/L
> >> never drops below 1 after it first rises above 1. I could avoid this
> >> problem by fitting a linear function in the points on the main
> >> sequence and determine the ZAMS by the first point which is below this
> >> linear fit. Unfortunately, this would not work for the 0.5 -1ish solar
> >> mass as the ratio converges from values above the main sequence value.
> >> What I could do is determing the ZAMS by finding the point which
> >> differs from the linear fit using the main sequence point by some
> >> value. Yet, I wonder if this stopping criterion would still be
> >> physical and not just some way to deal numerical issues?
> >>
> >> I have again attached a zipped folder of the plots that show what I
> >> refer to. Here i have plotted log_L and log_LH in the upper pannel and
> >> LH/L in ther lower pannel. Also the green line shows the determined
> >> ZAMS timestep which is the point on which the ratio drops below 0.9995
> >> when looking at the inverse time.
> >>
> >> Thank you in advance for any help!
> >>
> >> Thomas Steindl
> >>
> >>
> >> Zitat von Aaron Dotter <aaron.dotter at gmail.com>:
> >>
> >> > Hi Thomas,
> >> >
> >> > [Josiah beat me to it!]
> >> >
> >> > The ZAMS is a hard thing to define precisely.  What does it mean for
> the
> >> > project you're working on?
> >> >
> >> > You're seeing the different behavior because of the transition from
> >> > H-burning dominated by the pp chain vs. the CNO cycle.  The basic net
> >> > ignores several lesser species that equilibrate once the core gets hot
> >> > enough for the reactions to proceed.
> >> >
> >> > If it's acceptable for you to evolve slightly past the ZAMS and then
> >> > identify a previous timestep as the ZAMS, the following is the
> procedure
> >> I
> >> > use (in post-processing a MESA history file).
> >> >
> >> > Stop once the central H mass fraction has been reduced by 0.0015 from
> its
> >> > initial value.  Move backward from this point until you find the
> timestep
> >> > for which the model first L_H/L_tot crosses 0.99, or whatever you want
> >> your
> >> > ZAMS definition to be.
> >> >
> >> >
> >> > Cheers,
> >> > Aaron
> >> >
> >> >
> >> >
> >> >
> >> > On Thu, Mar 14, 2019 at 5:30 PM Thomas Steindl <
> >> > Thomas.Steindl at student.uibk.ac.at> wrote:
> >> >
> >> >> Hello,
> >> >>
> >> >> I am working on pre-MS Asteroseismology. Therefore, I am calculating
> >> >> MESA models which I use as input for GYRE. In my analysis, I need to
> >> >> know the timestep at which the star reaches ZAMS. Unfortunately, I
> >> >> fear the stopping conditions implemented in MESA do not work. To show
> >> >> this I have used three different inlists. A first, very simple inlist
> >> >> (Basic_inlist), an inlist with additional varcontrol
> >> >> (additional_varcontrol) and one with additional varcontrol and using
> >> >> the ppandcnoextras net instead of the basic net
> >> >> (additional_varcontrol_and_net). I have also attached the
> >> >> corresponding inlists. In the corresponding png files, I have plotted
> >> >> the values for log_L and log_Lnuc in the upper panel and the ratio
> >> >> L/Lnuc in the lower panel. As you can see, the ratio seems to
> converge
> >> >> to the value 1 for the first two inlists (for which this stopping
> >> >> criterion works). But for the latter of the three inlists, Lnuc
> >> >> exceeds L at some point in the evolution and the stopping criterion
> >> >> fails.
> >> >>
> >> >> The zip folder 'ZAMS_second_stop_option' contains plots for 30
> stellar
> >> >> models computed with the 'additional_varcontrol_and_net' inlist and
> >> >> different masses. In the 30 pngs in this folder I have plotted log_L
> >> >> and log_Lnuc in the upper pannel and
> >> >> abs(log(power_hburn)-log_surface_luminosity) in the lower panel. The
> >> >> title shows the mass of a specific model and the value of
> >> >> L_nuc_counter which states how many timesteps Lnuc/L has been between
> >> >> 0.99 and 1.01. As you can see, the value for the second stop option
> >> >> exhibits drops (mostly while log_Lnuc > log_L) which in terms makes
> >> >> this stop option unreliable and I don't see how it can function as
> >> >> global stop option for all masses.
> >> >>
> >> >> I have tried other options (gravitational energy, contraction speed,
> >> >> etc.), yet I cannot find a criterion. Do you have any idea on which
> >> >> stellar properties I could use? Any help would be greatly
> appreciated.
> >> >>
> >> >> Thank you in advance,
> >> >> Thomas Steindl
> >> >>
> >> >> _______________________________________________
> >> >> mesa-users at lists.mesastar.org
> >> >> https://lists.mesastar.org/mailman/listinfo/mesa-users
> >> >>
> >> >>
> >> >
> >>
> >>
> >>
> >
>
>
>
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