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

Aaron Dotter aaron.dotter at gmail.com
Wed Oct 18 10:11:00 EDT 2017


Hi Iñigo,

 but since I'm trying to replicate the results of previous works using a
> different code, I was expecting consistent results.
>

Unless you can verify that you are using the same physical assumptions in
MESA as in the other code you're trying to replicate, you are unlikely to
get similar results.  This is especially true for something like Teff that
is sensitive to factors that often vary among different stellar evolution
codes.

Important factors for Teff on the RGB/HB include, but are not limited to,
the mixing length parameter and the atmosphere boundary condition.  You
don't set either of these in your inlists so you're using MESA's defaults.
See if you can match these to what the other code used.



> I have another question that might help me in the next step. In my models,
> the position of the ZAHB almost doesn't vary in the HR diagram, despite
> increasing the eta_Reimers. Does this might be caused by any parameter that
> I'm not activating to take the winds into account during the RGB phase? The
> default values for cool_wind_on/off_T, as in controls.default, are
> cool_wind_full_on_T = 0.8d4
> cool_wind_full_off_T = 1.0d4
> If I understand it correct, the cool wind is then relevant below 8000K,
> and that's the range where the star is evolving. Is that correct? Having
> the cool_wind_full_off_t higher is confusing somehow, but I assumed that it
> was affecting only between ON and OFF.
>

Here is the relevant info from controls.defaults (for r9575).

         ! on for T\_phot < `cool_wind_full_on_T`
         ! off for T\_phot > `cool_wind_full_off_T`
         ! ramp from 0 to 1 between the two limits
         ! set `cool_wind_full_on_T = 0` to ignore the cool_wind

With your setting, which are the defaults, I would expect the cool wind to
be on during the RGB evolution.  MESA has a cool wind and a hot wind.  The
cool wind is designed to turn off *above* some temperature just like the
hot wind turns off *below* some temperature.  Hot > Cool so there is a way
in which this makes sense.


Cheers,
Aaron
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