[mesa-users] Horizontal branch and zahb

Sat Jul 30 18:03:09 EDT 2016

Hi Jeremy,

Aaron's suggestions are excellent, but I thought I'd go ahead and share some work I did on this that's just been gathering dust.  Perhaps you'll find something useful.

I split it into several inlists: pre ms to zams, zams to he flash, he flash to drop in L, and then the hb phase.

to adjust the ZAHB mass, I varied the wind on the RGB in the inlist_to_he_flash inlist
      cool_wind_RGB_scheme = 'Reimers'
      cool_wind_AGB_scheme = 'Blocker'
      RGB_to_AGB_wind_switch = 1d-4
      Reimers_scaling_factor = 0.42d0  
      Blocker_scaling_factor = 0.42d0  
      ! 0.7 gives tip mass of 0.507
      ! 0.5 gives tip mass of 0.605
      ! 0.42 gives tip mass of 0.64
      ! 0.4 gives tip mass of 0.65
      ! 0.3 gives tip mass of 0.69

you can also save time by using the model from this inlist adjusted to give the largest ZAHB mass you want, and then remove mass at the start of the inlist_to_zahb_RRLYR_Z0004 inlist.  it would be interesting to compare the two methods to see if are assumption is good that it doesn't matter when the mass is removed, before or after the He core flash.

my parameters are set up to match Fig 3c in this paper:

      ! match Xiong et al 1998, Fig 3C.
      initial_mass = 0.8
      initial_z = 0.0004
      initial_y = 0.2396 ! initial x = 0.76

I did the run on my current development version, but should work in a recent public release (e.g., 8845).

 The final inlist picks up when the luminosity has made its initial drop from the He core flash.  So there are still subflashes before He burning reaches the center, and those cause a few ups and downs in the HR before things settle down.  You can see that in these plots where age = 0 is at start of the run for this inlist, just after the initial drop in L.

Note that it makes loops through the instability strip, with the 1st happening before the He burning has reached the center.  When center He burning begins, the center follows a roughly constant P trajectory in T-Rho while the Teff drops returning back to the red of the instabilities.   You can check the center He4 mass fraction in the text at the bottom of the attached movie.  When the center He starts to burn, watch the center T-Rho location move.  Then the Teff starts to drop.  Fun to see all of this together in different panels of a movie.  

-Bill

On Jul 29, 2016, at 10:08 AM, Jeremy Sakstein wrote:

> Hi everyone
> 
> I have what I suspect is a really stupid question but not really being a stellar structure person I'm struggling a bit.
> 
> I'm trying to study RR Lyrae stars with Z=0.0001 so I've been studying the create_zahb and pre_zahb test_suite cases but the model has Z=0.02 so I'm trying to figure out how to repeat the process but failing miserably.
> 
> My ultimate goal is to create a Z=0.0001 0.75 M zahb star that I can use as a starting model to evolve differently (I'm changing a parameter related to a modified gravity theory) through the RR Lyrae instability strip.
> 
> If anyone can help me figure out which initial (pre_ms to near hb I suppose) model I should evolve to create the model that create_zahb can use to make the starting model I'm after I would really appreciate it. Ideally, I'd like to start outside the blue edge and evolve through it.
> 
> Cheers,
> 
> Jeremy
> 
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> mesa-users at lists.sourceforge.net
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