[Mesa-users] Rotation in massive stars

Fri Mar 11 12:35:53 UTC 2022

Hi Simon,

I've just tried this parameters, and the result is the same, slow down and
never rises up again. I waited to see what happened on the cool sie (RSG)
but it remains down.

My scientific goal is to model an LBV, so I'm using MLT++. I'm trying to
include rotation in my models to make them more realistic, but I've
realized that it doesn't matter if I'm working with an LBV or with any kind
of massive star, because I found the same result, and that is: beyond
nearly the end of MS the surface rotation v never rises up again, that's
why I asked for this in a generic way, for any massive star.

The radius goes up and down, so does contraction... I expected a behavior
for surface rotation going more or less up and down, but it goes only down
once and remains there, that's why I was wondering if I was using the
proper parameters.

Thank you for your answers, if you or anyone else have more tips, those are
very welcome!

Thanks again,

Silvana

El vie, 11 mar 2022 a las 12:02, Simon Murphy (<simon.murphy at sydney.edu.au>)
escribió:

> Hi Silvana,
>
> It sounds like the star is rotating so fast in the early evolution that it
> is not really reaching the main sequence: it's exceeding its breakup
> velocity and thus not finishing its pre-main-sequence contraction fully.
>
> What I imagine happens in a real rapid rotator is that angular momentum is
> transferred to the surface layers somehow. This angular momentum could come
> from an initially more rapidly rotating interior, which is what would
> result from contraction of a uniformly rotating protostar. However, I don't
> understand the transport mechanisms well enough to advise, nor how to
> implement this in MESA.
>
> One thing you could try with MESA (r15140) is to set the rotation as late
> as possible, e.g. using the near_ZAMS flags. That would look something like
> this
>
> ! initialise rotation at the ZAMS
> new_rotation_flag = .false.
> change_rotation_flag = .false.
> set_surface_rotation_v = .false.
> set_near_zams_surface_rotation_v_steps = 50
> near_zams_relax_initial_surface_rotation_v = .true. ! other flags have to
> be false for this to work.
> new_surface_rotation_v = 200 ! km/s
>
> Then, if you wanted to spin up the star again later in the evolution, you
> could save this model at some age, then load with a different inlist where
> you use change_rotation_flag = .true.
>
> I'm not sure if it's possible to keep the surface rotation fixed in other
> ways, and of course, the arbitrary spin-up is not physical either. But
> without understanding your ultimate science goals, I'm unable to comment on
> whether that's important.
>
> Good luck!
>
> - Simon
> ------------------------------
> *From:* Silvana Vacchina <silvana.astrophysics at gmail.com>
> *Sent:* 11 March 2022 20:29
> *To:* Simon Murphy <simon.murphy at sydney.edu.au>
> *Cc:* mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
> *Subject:* Re: [Mesa-users] Rotation in massive stars
>
> Hi Simon,
>
> Thank you very much for your answer.
>
> If I try to rotate faster from the beginning, the MS is chaotic, it seems
> that the star doesn't want to go to the red side and instead goes to
> collapse in any strange way.
>
> What I really don't know is if I'm using the proper parameters... If this
> is the case then I accept that the increasing radius slows the star... is
> just that I don't know why there are some massive stars which are fast
> rotators, I don't know which parameters can give me that.
> Maybe it's just a misunderstanding on my part, and I'm not understanding
> in which exact phase or moment in the evolution you can get more rotation.
>
> And I don't know which parameter can keep rotation rate fixed. Any more
> tips regarding parameters would be really appreciated.
>
>
> Thanks,
>
> Silvana
>
>
> El jue, 10 mar 2022 a las 23:00, Simon Murphy (<simon.murphy at sydney.edu.au>)
> escribió:
>
> Hi Silvana,
>
> Rotation will slow down because the star's radius increases as it evolves
> on the main sequence. The star also gets a denser core as the mean
> molecular weight there increases. Conversation of angular momentum
> therefore suggests the surface should spin down but the core should spin
> up, unless you are using some physics to redistribute angular momentum
> throughout the star.
>
> Forgive me for asking, but why do you not want to evolve the star in this
> way, and to keep the rotation rate fixed, instead?
>
> If you are aiming to have v=300km/s at the TAMS, you might have to start
> your star rotating faster so that it has slowed to 300km/s at the TAMS.
>
> - Simon
> ------------------------------
> *From:* Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of
> Silvana Vacchina via Mesa-users <mesa-users at lists.mesastar.org>
> *Sent:* 11 March 2022 02:00
> *To:* mesa-users <mesa-users at lists.mesastar.org>
> *Subject:* [Mesa-users] Rotation in massive stars
>
> Dear MESA users,
>
> I'm working on a project for a master degree and I would like to include
> rotation into my massive stars models, but I've realized that rotation slow
> down till one factor or less near the end of main sequence (MS) and never
> rises up again.  Rotation parameters are a bit complicated to me, and I'm
> not sure if I'm using them properly.
>
> I'm using r15140 and I've run several combinations of parameters without
> success, with a goal to keep a rotation v at around 300 km/s till He core
> burning, if that's possible.
>
> Could someone give me some tips on this? Am I missing a parameter maybe?
> Any help is appreciated.
>
> Thanks in advance,
> Silvana
>
>
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