[mesa-users] questions about the "Eulerian" scheme for eps_grav

[Masanobu Kunitomo]

Dear all,


I would like to ask two questions about (1) changing the region of “Eulerian scheme” (s% k_below_Eulerian_eps_grav) and (2) the validity of the Eulerian scheme. I am using ver. 6596 and working on a protostar’s evolution with intense accretion (the mass accretion rate is 1e-5Msun/yr and CpTMdot/L is at most ~100).


(1)
I would like to try the case that eps_grav is calculated by the “Eulerian” scheme in the entire star, namely s% k_below_Eulerian_eps_grav = s% nz (although this may not be good because the Eulerian scheme can cause a numerical diffusion). 
I tried to set a large “min_dxm_Eulerian_div_dxm_added” in the inlist file, but this did not work. Next I tried to modify the subroutine "set_Eulerian_Lagrangian_for_eps_grav” in “mesa/star/private/evolve.f”. I tried some modifications such as “dxm_kA = s% xmstar”, but it did not work. (In fact, even if I write “stop”, it was not reflected...) Is it inappropriate to modify the evolve.f file?

(2)
If my understanding is correct, in the Eulerian scheme, the newly accreted mass is distributed in the entire star uniformly and instantaneously, and its entropy is assumed to match the local value of the stellar interior as shown in the Fig. 6 of Sugimoto et al. 1981 (I have attached this figure). If the star is radiative, the accreting material’s entropy can be much lower than that of the stellar surface. Thus, I think this underestimates the accreting material’s entropy. Is this correct?



I apologise if these are already discussed in this mailing list. 
I appreciate any comments. Thanks in advance!

Best wishes,
Masanobu

--
Masanobu Kunitomo
Ph.D. student / JSPS Research Fellow
Tokyo Institute of Technology
Dept. of Earth and Planetary Sciences
Email: kunitomo at geo.titech.ac.jp

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