[Mesa-users] Finding ZAMS

Fri Mar 15 13:53:37 EDT 2019

Hello,

thanks to all of your input.

First, it seems that the criterions of minimus radius and maximum  
log_g work a little bit better, but again fail for specific masses. I  
have attached corresponding plots in a zip file.

Well the properties of a star on the main sequence include as far as I  
know thermal and hydrostatical, constant burning of hydrogen in the  
star, constant total gravitational energy, etc. I have tried to  
incorporate some of this conditions, yet I failed. I also tried to  
look at the abundances of the components of the cno- and pp-cycle  
(C12, O16, ..). So far I am out of ideas but looking forward for any  
suggestions! :)

Again, thank you all for your time!
Thomas

Zitat von Aaron Dotter <aaron.dotter at gmail.com>:

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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: radius_and_log_g.zip
Type: application/x-zip-compressed
Size: 588397 bytes
Desc: not available
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20190315/5014dc03/attachment.bin>