[mesa-users] questions about the time steps

[Masanobu Kunitomo]

Dear all,

I am using MESA version 4798 and I have two questions about the time steps.

1.
I am interested in the PMS evolution with a intense episodic accretion onto a star from ~0.01Msun to a 1Msun.
When I calculate it, I have to limit the time steps in order not to make them larger than the duration of burst (accretion) phase, using the "max_timestep" parameter.
I realized that the evolutions can be (sometimes significantly) different according to the maximum time steps.
Do you know the reason?

It can be seen especially when I use the large mass accretion rate (>~ 5e-6Msun/yr) and time steps are limited by "L_div_CpTMdot".


2.
I have another question.
The entropy of the accreting materials is determined by the compressional heating.
Why the time steps are limited by the compressional heating, i.e., "L_div_CpTMdot"?

This corresponds to the ratio of the accreting and thermal timescale, but this is not dependent on the time step.

Moreover, I know the compressional heating assumes that thermal (KH) timescale is much shorter than the accreting timescale. However, in our case this assumption is not valid, even though I can calculate the PMS evolution with a high mass accretion rate.
So I am wandering the result in MESA under the too high mass accretion rate is reliable.


Sincerely,
Masanobu Kunitomo

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