[Mesa-users] Setting the value of omega/omega_critical

[Warrick Ball]

Hi Antonio,

If you aren't interested in the structural effects of rotation, you can incorporate a rotation rate when you compute the pulsations, rather than in MESA.  If you're computing frequencies with GYRE, you can impose a constant rotation rate by setting

     Omega_rot_source = 'UNIFORM' ! rather than the default 'MODEL'
     Omega_rot = 0 ! your choice
     Omega_rot_units = 'NULL' ! your choice

in the `&rot` part of the namelist.  See

     https://gyre.readthedocs.io/en/stable/ref-guide/input-files/rot-params.html

If you want a differential profile, then you can save the pulsation data in "GYRE" format and set the values of the relevant column in the data file to whatever rotation profile you want before computing the frequencies.

I don't know how other oscillation codes handle rotation profiles.

As said though, this all ignores the structural effects of rotation, but it might be what you need.

Cheers,
Warrick


___________

Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
W.H.Ball at bham.ac.uk
+44 (0)121 414 4552

On Fri, 25 Mar 2022, mesa-users at lists.mesastar.org wrote:

> 
> Hi Simon,
> 
> 
> Thanks for your time. What I want to do is obtaining the pulsation frequencies of some stars at some given values of their omega (in different moments of each star), so I think I will have to save and restart as you say to be able to perform the
> work.
> 
> 
> Thank you again for all!
> 
> 
> Antonio Varo
> 
> 
> 
> 
> On 25/3/22 2:27, Simon Murphy wrote:
>       Hi Antonio,
> 
> omega will always change as a function of time because angular momentum is conserved and the stellar structure is not constant. The star becomes more centrally condensed and the radius increases.
> 
> So while your initialisation of rotation will achieve a certain value of omega/omega_c at some point, it will not stay that way for long. Moreover, the star will not remain a uniform rotator, either. If you're able to plot the internal rotation
> rate as a function of (r/R) at a few ages, this will become apparent, especially while the star is still contracting.
> 
> The meaningful question then becomes 'what do you hope to achieve'? That is, given the options, do you want to initialise uniform rotation at some age and let it evolve as perhaps a star would? Or do you want to force uniform rotation
> throughout the evolution, which might be achieved with a further save&restart with a renewed fixed omega/omega_c some time around your model 600 (and perhaps 700 too)? Or something else entirely?
> 
> - Simon
> 
> __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
> From: AVG <avargar2 at hotmail.com>
> Sent: 25 March 2022 01:10
> To: Simon Murphy <simon.murphy at sydney.edu.au>; mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
> Subject: Re: [Mesa-users] Setting the value of omega/omega_critical  
> 
> Hello Simon!
> 
> 
> Firstly, thank you very much for your time.
> 
> 
> I attach the plots (Figure_5*) of the stellar radius, the nuclear burning and the original plot (just to make it easier to compare).
> 
> 
> I don't know how to take these plots. I see that the radius decreases (and so the omega increases). However, this situation doesn't change when I run the simulation for 2500 Myears (for example), and I always get a changing value of the omega.
> I also attach the plots of the simulation that ends at 2500 Myears (Figure_1*).
> 
> 
> Best regards,
> 
> 
> Antonio Varo
> 
> 
> 
> On 23/3/22 22:33, Simon Murphy wrote:
>       Hi Antonio,
> 
> you're setting rotation using the near_zams parameters. I think it's important to note that this is not the same as 'after the ZAMS'. I suspect the star is still contracting a little, which is why the rotation is still increasing after it
> is initially set.
> 
> To confirm (and for the benefit of future readers), please could you plot what's happening with (a) the stellar radius, and (b) the nuclear burning, alongside your rotation plot?
> 
> cheers,
> - Simon
> 
> __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
> From: Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of AVG via Mesa-users <mesa-users at lists.mesastar.org>
> Sent: 24 March 2022 04:34
> To: mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
> Subject: [Mesa-users] Setting the value of omega/omega_critical  
> Dear all,
> 
> I am trying to simulate a rotating star with a given value of its
> omega/omega_critical, but I find that this parameter varies strongly in
> the first 20 Myears of the simulation since the ZAMS starts (I am
> specially interesed on what happens in those first 20 Myears after the
> ZAMS, as the work I am doing is focused on some previous results
> obtained until that time).
> 
> In my simulations I turn on the rotation at the begining of ZAMS, and
> shortly after it starts the value of its omega changes quickly, as we
> can see in the image I attach. I want to set the value of the omega
> along the simulation, as I need to analyse results obtained with GYRE
> for some specific omegas (so the increasing behaviour of the omega makes
> it really difficult for me).
> 
> I also attach the inlist I have used.
> 
> Could someone give me some tips on this?  Any help will be appreciated.
> 
> Best regards,
> 
> Antonio Varo
> 
> 
>