[mesa-users] secular modes with GYRE

[alfred at gautschy.ch]

Rich,

thanks for the pointer to the hidden treasure in &osc! This is the  
basic trick I looked for. I will play around with it.

> There already is some support in GYRE for this kind of calulation.  
> In the &osc namelist group, there is an (undocumented) parameter  
> ‘time_factor’ which allows one to control the assumed time  
> dependence of modes. The two options are ‘OSC’, which has time  
> dependence proportional to exp(-i omega t), and ‘EXP’, which has  
> time dependence proportional to exp(-omega t). The ‘EXP’ option in  
> effect allows one to scan along the imaginary frequency axis, which  
> I use when searching for dynamically unstable modes.

The above is potentially helpful also to the broader stellar-evolution  
community.
The rest that follows is indeed more of shop-talk for your GYRE-Forum,  
so I keep my mouth shut on that here.

Alfred


> The more general case of scanning along an arbitrary line in the  
> complex plane isn’t supported by GYRE, but there are some  
> (experimental) executables that ship with GYRE, which provide this  
> sort of functionality. In particular, the file  
> gyre/src/frontend/gyre_map.fpp allows a 2-D sampling of the  
> discriminant D(omega) over the complex plane, which is a robust way  
> to find very non-adiabatic modes. Attached below for your amusement  
> is a map showing the real(D)=0 (blue) and imag(D)=0 (red) contours  
> for radial modes in a massive star, as calculated using gyre_map.  
> The crossings of these contours correspond to the star’s modes. Note  
> the almost-complex-conjugate pairs of modes — we’re in the NAR limit  
> here!
>
> To build gyre_map, all you need do is download the most recent  
> release candidate of GYRE (5.0rc3), edit gyre/src/build/Makefile to  
> add gyre_map to the definitions of the TARGETS variable, and then  
> build as usual; gyre_map will then be placed in gyre/bin. An example  
> of gyre_map in action is given in the gyre/test/map directory; just  
> do ‘./gyre_map gyre_map.in’ to run the example. The resulting map.h5  
> file can be plotted as a contour map using the plot_map.py python  
> script in the same directory.
>
> Since this is a very GYRE/pulsation specific topic, perhaps we  
> should take further discussion to the GYRE forums (unless people on  
> the MESA list want to hear about very non-adiabatic modes and the  
> numerical challenges they present?).
>
> cheers,
>
> Rich
>
>