[mesa-users] Overshooting

[Richard Townsend]

Hi Folks —

Rob raises an important point here: the scale height for exponential overshoot is typically much smaller than for ‘equivalent’ step overshoot. See the discussion in Herwig (2000, A&A, 360, 952).

cheers,

Rich

> On Jun 2, 2015, at 11:49 AM, Robert FARMER <rjfarmer at asu.edu> wrote:
> 
> Hi
> Firstly it would help to say what about the plots you think isn't very good.
> 
> Secondly a overshoot of 0.1 is very big, the cannonical (but no means the "real" value) is usally quoted as 0.016. Maybe  a smaller value will help
> 
> Next, the definition for MESA's ovbershoot is that you take the convective mixing coefficent at _f0_ scale heights before the edge of the convective zone and it extends for _f_ scale heights starting from _f0_. So by setting f0=f, your overshoot isn't actually overshooting the convective boundary. Perhaps you could also try:
> 
> Setting _f0_ values to 0.05 and _f_ values to 0.15, if you want to stay with your overshoot values, such that the overshoot region starts inwards of 0.05, extends for 0.15 scale heights (which is 0.1 scale heights pass the convective oundary)
> 
> Regards
> Rob
> 
> 
> On Tue, Jun 2, 2015 at 8:34 AM, Kenny Van <kvan at ualberta.ca <mailto:kvan at ualberta.ca>> wrote:
> Hi, I was trying to produce some results using overshooting and it seems as though regardless of timestep the plot produced doesn't seem very good. I have attached the three plots I created using my data. The overshooting and changes in timestep are said in the title. But just in case I will list all the properties of the star.
> 
> &star_job
>   
>     mesa_dir = '/home/kvan/mesa_svn'
>   
>     create_pre_main_sequence_model = .true.
> 
> / !end of star_job namelist
> 
> 
> &controls
> 
> ! initial parameter
>   
>   ! initial mass of star
>     initial_mass = 20.0
> 
>   ! initial metallicity of star, MESA only goes from 0 to 0.04
>     initial_z = 0.014
> 
>   ! initial helium mass fraction of star
>     initial_y = 0.266
> 
>   ! changing the MLT to match that in Meynet
>     mixing_length_alpha = 1.6
> 
> ! overshooting
> 
>   ! all exponential overshooting is by default zero
>   ! setting step overshooting
>     step_overshoot_f_above_burn_h = 0.1
>     overshoot_f0_above_burn_h = 0.1
>     step_overshoot_f_below_burn_h = 0.1
>     overshoot_f0_below_burn_h = 0.1
>     step_overshoot_f_above_burn_he = 0.1
>     overshoot_f0_above_burn_he = 0.1
>     step_overshoot_f_below_burn_he = 0.1
>     overshoot_f0_below_burn_he = 0.1
>     step_overshoot_f_above_burn_z = 0.1
>     overshoot_f0_above_burn_z = 0.1
>     step_overshoot_f_below_burn_z = 0.1
>     overshoot_f0_below_burn_z = 0.1
> 
> ! Mass loss
>   
>   ! Changing mass loss so system acts like that of Ekstrom et al.
>   ! Use Vink mass loss rate
>     RGB_wind_scheme = 'Vink'
>     Vink_wind_eta = 1
> 
> ! timestep limits
>   ! Limit magnitude of max change in log10 total pressure in any cell
>     delta_lgP_limit = 0.2
> 
>   ! Limit magnitude of max change in log10 temperature in any cell
>     delta_lgT_limit = 0.2
> 
> ! when to stop
> 
>   ! max timestep size
>     max_years_for_timestep = 500
> 
>   ! stop when we reach AGB to produce similar results to Maynet et al.
>     stop_at_TP = .true.
> 
>   ! max age
>     max_age = 1.0d10
> 
> / ! end of controls namelist
> <20M_Low_Lim_noOS_5d5.png><20M_Low_Lim_OS_5d5.png><20M_Low_Lim_OS_500.png>
> 
> Thanks
> 
> ------------------------------------------------------------------------------
> 
> _______________________________________________
> mesa-users mailing list
> mesa-users at lists.sourceforge.net <mailto:mesa-users at lists.sourceforge.net>
> https://lists.sourceforge.net/lists/listinfo/mesa-users <https://lists.sourceforge.net/lists/listinfo/mesa-users>
> 
> 
> ------------------------------------------------------------------------------
> _______________________________________________
> mesa-users mailing list
> mesa-users at lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/mesa-users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20150602/be44ff91/attachment.html>