[Mesa-users] Finding ZAMS

[Thomas Steindl]

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
>> >>
>> >>
>> >
>>
>>
>>
>