[Mesa-users] Querying MESA Results

[Aaron Dotter]

Hi Jessie,

The "spike" you observed is due to the pre-main sequence contraction of the
star.  This is a brief phase compared to the main sequence, as you've seen,
when the star has yet to begin sustained nuclear reactions in the core.
This contraction happens on the Kelvin-Helmholtz timescale until the center
reaches conditions suitable for nuclear reactions.

If you only want to consider the main sequence, then you can examine the
output to find when the H-burning luminosity becomes roughly equal to the
total luminosity.  That's a good, basic definition of the zero age main
sequence (ZAMS).

The simulation has to start somewhere and the very early evolution does
begin at t=0.  The evolution at very early times (10^-5) is
*numerically* accurate
(at some level) as far as solving the equations are concerned but it is not
*physically* accurate because there are aspects of the very early evolution
of stars that we don't model very well (in one dimension or otherwise).

I hope this helps!  If not, feel free to ask more questions.

Aaron

On Wed, Nov 25, 2020 at 7:25 AM Jessie Hogan via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

>
>
>
>
> Hi there,
>
>
>
> I am wondering if you would kindly offer some insight into some puzzling
> MESA results that I obtained.
>
> Myself and my professor Ian Crawford could not figure out why there is a
> ‘spike’ in the plots I gained for habitable zone (HZ) boundaries utilising
> MESA’s stellar evolution age, radius and effective temperature output
> values into a HZ formula that looks like this:
>
> Here is the plot below, and the ‘spike’ within the first 20,000 years in
> greater detail:
>
>
>
>
>
>
>
>
>
> Our initial thoughts were that this could be because the program is
> reliable in predicting very early phases of evolution, hence why MESA gives
> output values for 1.00E-5 years of a star’s lifetime? Or could it be that
> this is predicted behaviour for very young stars that just joined the ZAMS?
> In which case where does the program begin its evolution?
>
>
>
> Any insight would be very much appreciated as this work forms a part of my
> final dissertation in my undergraduate degree, and of course credit will be
> given.
>
>
>
> Kind Regards
>
> Jessie Hogan
>
>
>
> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
> Windows 10
>
>
>
>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20201125/cc9dbb43/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 859F0D4D7E7744A4992B2253E35A7AA6.png
Type: image/png
Size: 13937 bytes
Desc: not available
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20201125/cc9dbb43/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 1F14AC7329AC40F7B407620831064A85.png
Type: image/png
Size: 63862 bytes
Desc: not available
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20201125/cc9dbb43/attachment-0001.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0DEFD55D06C34387B726A07C51166EAF.png
Type: image/png
Size: 77253 bytes
Desc: not available
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20201125/cc9dbb43/attachment-0002.png>