[Mesa-users] Heavy element profile

[valletta]

On 2019-01-11 21:45, Evan Bauer wrote:
> Hi Claudio,
> 
> I agree with Frank that for you application, it sounds like you’re
> better off using the accretion controls.
> 
> But I also think it might be helpful to explain a little more why MESA
> isn’t behaving as you expected. The basic problem is that X, Y, and Z
> aren’t the fundamental composition variables in the star pointer. They
> are calculated based on the entire network of isotope mass fractions
> each step. So if you want to change composition by hand, you need to
> edit s% xa (see $MESA_DIR/star/public/star_data.inc). Then you’ll see
> X, Y, and Z in your model change accordingly.
> 
> Cheers,
> Evan
> 
> 
> 
> 
>> On Jan 11, 2019, at 6:12 AM, Francis Timmes via Mesa-users 
>> <mesa-users at lists.mesastar.org> wrote:
>> 
>> one could try accreting material of a specified composition
>> 
>> http://mesa.sourceforge.net/controls_defaults.html#composition_controls
>> 
>> fxt
>> 
>> 
>> 
>> 
>>> On Jan 11, 2019, at 3:06 AM, valletta <valletta at physik.uzh.ch> wrote:
>>> 
>>> Dear MESA users
>>> 
>>> Hello. I am modelling the evolution of a giant planet, I start the 
>>> model with a given composition of X, Y and Z, constant through the 
>>> envelope. Now I need to modify these compositions at every time-step, 
>>> depending on the accretion of heavy element by the planet, and the 
>>> amount of X,Y and Z must depend on the position of the layer in the 
>>> envelope (so, a non-constant profile through the envelope). My idea 
>>> to do that was to go in the run_star_extras file and write something 
>>> like
>>> 
>>> for(i = 1, i< layer number)
>>> 
>>>  s% x(i) = new x(i)
>>>  s% y(i) = new y(i)
>>>  s% z(i) = 1 - new x - new y
>>> 
>>> the problem that I have is that these values are not saved by mesa, 
>>> but at every time step the code restart from the initial profile of 
>>> X,Y and Z.
>>> 
>>> Thank you in advance for every help
>>> 
>>> Best,
>>> Claudio
>>> _______________________________________________
>>> mesa-users at lists.mesastar.org
>>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>>> 
>> 
>> _______________________________________________
>> mesa-users at lists.mesastar.org
>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>> 

Thank you both for your answers.
In my simulation, the heavy elements are accreted in the form of big and 
compact objects (planetesimal) that deposit their mass falling towards 
the planet's core through ablation due to the gas drag of the envelope's 
gas. As a result, I need to specify where the high-Z material is 
accreted, while, if I remember correctly, with the accretion implemented 
in Mesa the mass is accreted at the top of the envelope. Can I specify 
with the accretion control in which layer accrete the high-Z material? 
If not, what is the most straightforward way to do it?

Thank you again,
Claudio