Confusing Xi_r results upon testing solar Model S

[JackMuir]

I've been testing gyre on the standard solar Model S. My objective is to compute the derivatives of the mode displacement eigenfunctions. To give fair warning, this is my first foray into asteroseismology so it is quite possible that I have something seriously wrong in my understanding. With that caveat in mind, I have computed the l = 0-3 modes in the 1-10 mHz range using model S supplied in fgong format from Jorgen Christensen-Dalsgaard's website. When I look at, for example, the mode output for the first l=0 mode in this range, we see that at a fractional radius of about 1, the xi_r displacement rises to be on the order of 100. The documentation on the output variables page on the gyre wiki indicates that that this xi_r displacement perturbation is in units of the stellar radius. I can think of 3 possibilities for this problem: either I don't understand what Xi_r represents, which is entirely possible; the units in the documentation are incorrect; or there is something wrong with gyre, either on my computer or in general. I've attached the input file and an example mode output. If anybody has an idea as to what has occurred here, the information would be much appreciated.

Cheers,

Jack Muir

[rhtownsend]

Hi Jack --

Thanks for the post. I haven't looked at your attachments yet, but I think I can explain what's going on. Because GYRE (like almost all other oscillation codes) is a linear code, the overall normalization of eigenfunctions is arbitrary. That is, if xi_r(r) is an eigenfunction, so are 0.001*xi_r and 1000*xi_r.

GYRE adopts the convention that eigenfunctions are normalized so that the global mode inertia (in units of M R^2) is unity --- this is discussed in section 4.6 of the GYRE paper (http://adsabs.harvard.edu/doi/10.1093/mnras/stt1533). But you can re-normalize them post-hoc to any value you like, and they will still satisfy the linearized pulsation equations.

I hope this explains!

cheers,

Rich