[mesa-users] create_zahb and relax

[Bill Paxton]

On Mar 28, 2015, at 7:16 AM, Cyrus Zalian wrote:

> Hi to all mesa-users,
> 
> As I already mentionned in a precedent question, I would like to study RR Lyrae stars using MESA.
> 
> I've run several model from preMS to a core He limit of 10e-5 as suggested by Aaron.
> 
> The problem is, that for the moment, it takes a rather long time (hours) to compute each model.
> 
> So I had an idea : why not start from the create_zahb model in test_suite ?
> 
> So all in all, here are my question
> 
> 1) Is it a good idea ?
> 
> 2) Is there a minimum/maximum masses for which the program will work ?
> 
> 3) The program starts loads pre-zahb.mod model, but we don't have any information about this model ? How did we obtain it ? How can I have detail about this model ?
> 
> 4) Linked to the last question : I want to study the influence of mass but also the influence of metallicity. This is why I need to know the initial value of Z. Now, if I want to use another value of Z, how should I do ? Has relax_Z anything to do with it ? Is it a good idea ?
> 
> Thank you all in advance for your response.


Hi,

It is a great idea to use the create_zahb to get started.  But rather than use it as a black-box, look inside and study how it works until you have a clear understanding of what's going on.  At that point, you'll probably decide to do-it-yourself based on what you've learned rather than directly use the test_suite code.  

The basic idea is that the core evolution going up the RGB seems to be pretty much independent of the envelope mass -- i.e., the helium core flash happens when the core reaches a certain mass independent of the total mass of star (as long as the total mass is in the range that leads to a He flash).  So for a particular Z, you pay the price of evolving up the RGB to the flash with little or no mass loss.  Then save a model just after the flash for later reuse.  To make various horizontal branch models, you start from that saved, post-flash model and adjust a strong wind to remove envelope to give you the HB mass you want.

Have fun!

-Bill





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