Re: mesa-users] Manual Change of Accretion Composition

[Bill P. <pa...@ki...>]

Hi Max,

The change in accretion composition should be fine.  Perhaps the problem is the abrupt start of accretion at the 5d-9 rate.

Let's separate the 2.   What happens if you do the 5d-9 mass change without changing the accretion composition?

Also, you should try manually turning up the accretion rate while keeping the timestep small.

Try something like max_years_for_timestep = 1d-7 to start with, and mass_change = 1d-12 -- or whatever it
takes to get things to converge.   (BTW: I'm assuming that everything works without accretion turned on, right?)
Let things run for a while until it is happy (i.e., running at max allowed timestep).   Then start increasing the
mass_change -- at each increment, let it run until it is happy, then increase again.  Once you reach the
desired accretion rate, remove the limit on max_years_for_timestep.

This is a crude manual version of what the various "relax" operations do.  And if you feel ambitious, you can
write your own relax routine to do "relax_to_mass_change".

Let me know how it goes.

-Bill





On Jul 2, 2010, at 6:46 AM, Max Katz wrote:

> Hello,
> 
> In an attempt to create my own nova, I used the model 1.000_Tc_3e7.mod in mesa/data/star_data/white_dwarf_models. This is a pure C/O white dwarf of 1 solar mass. The goal is to get it to go nova, so I set an accretion rate of 5 x 10^-9 (units are solar masses per year). However, the default behavior for accretion is to use the same composition for the accreted matter as there is on the surface. Since adding C and O to the surface wouldn't yield the nova I was looking for, I set the following in the controls namelist:
> 
> mass_change = 5d-9
> accrete_same_as_surface = .false.
> accretion_h1 = 0.75
> accretion_h2 = 0.
> accretion_he3 = 0.
> accretion_he4 = 0.25
> 
> However, when I try to run with these settings on, the run cites "adjust_mass_failed", and crashes after hitting the default max number of backups (15). I tried the same settings on a different case and got the same error. If anyone has experience with changing the accretion composition, I would appreciate it if you could give some insight as to what I might be doing wrong. Thanks.
> 
> Max Katz
> Rensselaer Polytechnic Institute
> Physics, Class of 2011
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