[Mesa-users] Difference between "setting" and "relaxing" rotation

Pablo Marchant pamarca at gmail.com
Wed Jul 17 16:43:02 EDT 2019

Hi Nick,

The non-relax options mostly try to reach the target omega in one go.
Essentially, if we know the moment of specific moment of inertia i_rot of a
shell, i_rot, the specific angular momentum of the shell can be set to
i_rot*omega_target to obtain the required omega. This would work perfectly
if i_rot would be independent of the rotation rate, but because it isn't,
you should expect a discrepancy between the desired and resulting omega.
The set_omega_step_limit option just allows the setting of omega to be
repeated in multiple steps, which can potentially result in a better match
between the requested omega and the one finally set.

The relaxation methods operate in a different way. They attempt to reach a
target omega in a series of steps rather than trying to set it up in one
go. So, for instance, if the relaxation procedure is to take 10 steps and
you start from a non-rotating star, each successive step would try to set
omega slightly closer to omega_target, say 0.1*omega_target on the first
step, 0.2*omega_target on the second step and so on. In practice this is
not done linearly with the number of steps, but just trying to illustrate
the idea.

Hope that answers your question.


On Wed, Jul 17, 2019 at 3:33 PM Nicholas J Nelson via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> I'm working on a project that is looking at the effects of rotation on
> main sequence evolution and I've run into a question I can't seem to answer
> from the documentation. There appear to be two ways to activate rotation in
> Mesa -- namely one can use the group of inputs that begin with 'set' (e.g.,
> set_omega, set_omega_step_limit) or one can use another group of inputs
> that begin with 'relax' (e.g., relax_omega, num_steps_to_relax_rotation).
> What is the difference between setting and relaxing?
> Thanks,
> Nick
> Nicholas J. Nelson
> Assistant Professor of Physics
> Faculty Adviser, Society of Physics Students
> California State University, Chico
> njnelson at csuchico.edu
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users

Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
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