# [Mesa-users] Calculating R Parameter (t_HB/t_RGB) in GC by interpolating stellar evolutionary tracks

Aaron Dotter aaron.dotter at gmail.com
Tue Oct 17 21:17:47 EDT 2017

```Hi Iñigo,

It seems you have a number of assumptions that are at odds with what the
models are telling you.  Your best course is to go through each step of
your analysis and make sure that your results are correct and then check

You haven't said what the masses of the stars are at the ZAHB.  If the
masses are similar, then the temperatures may be too.  What happens if you
increase the Reimers factor again?  Your models may reach the ZAHB (as
defined by what happens in the core) without reaching a certain Teff at the
surface.  There's nothing wrong or unusual with that.

I think it would be very good for you to find where the number logT=3.85
comes from, what exactly it refers to, and how it relates to the models
you're making.

Please try these suggestions and then, if you have any problems with MESA,
come back and ask for help.

Cheers,
Aaron

On Tue, Oct 17, 2017 at 6:46 PM Iñigo Muñoz Elorza via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> OS: macOS SIerra 10.12.5
> MESA version: r9575
>
> Dear community,
>
> I'm trying to calculate the R parameter in GC by obtaining the
> evolutionary tracks of a star of 0.82 Msolar with different eta_Reimers
> mass loss factors, and then interpolating the solution at Log_T_ZAHB =
> 3.85, which has been determined by different observational data for that
> kind of stars.
>
> Trying to replicate the results from some previous work by Ayala, I'm
> considering:
> - initial_mass = 0.82
> - initial_Y = 0.248
> - initial_Z = 0.001
> - and Reimers_scaling_factor = 0.2 (or 0.35), depending on the case.
>
> The problem is that I obtain a value of T_ZAHB lower than 3.85 for both
> cases, and it should be higher for the case of eta_Reimers = 0.35, but I'm
> not sure what control parametrs I'm not taking into account.
>
> I'm attaching the inlist for both cases, together with the Python script
> to calculate R. With my current runs, those are my resuts:
>
>
> *eta_Reimers = 0.2*
> V_ZAHB: 0.549654103615
> T_ZAHB:  3.71087121492
> t_HB:  80.6521275821  My
> t_RGB:  55.9783179064  My
> R parameter:  1.44077440335
>
> *eta_Reimers = 0.35*
> V_ZAHB: 0.685704604046
> T_ZAHB:  3.72446361968
> t_HB:  82.1772995776  My
> t_RGB:  61.9668190125  My
> R parameter:  1.32615004106
>
> Any ideas why the T_ZAHB are so similar? The t_RGB is also quite
> different, and should be almost the same for both cases.
>
> I have also "experimented" with the parameters modified in the test_suites
> create_zahb, he_core_flash and hot_cool_wind (opacities, MLT,
> photospheres), but I haven't seen any improvement on the T issue (of
> course, the results were different for the different times).
>