Stellar models

Stellar oscillation programs require stellar models stored in specific formats. tomso provides functions to save and load files in these formats and to convert between formats.

FGONG is a well-established plain-text format used to provide input stellar models for oscillations codes. The definition evolved over time but the contents now haven’t changed in many years.

MESA produces files in what it calls GYRE-format and GYRE calls MESA-format. I refer to these as GYRE stellar models, not to be confused with the HDF5 files that GYRE supports.

ADIPLS expects stellar models in its own specific Fortran binary format, which I refer to as AMDL format. ADIPLS provides its own tool to convert from FGONG (usually fgong-amdl.d), which tomso mimics when converting FGONG objects to ADIPLSStellarModel objects using FGONG.to_amdl(). Note that AMDL files only contain data necessary to compute adiabatic oscillations (so no temperature, luminosity, etc).

All of these formats have some scalar data that is fixed for the whole stellar model (e.g. the total mass) and point-wise data that varies through the star (e.g. the pressure and density). The APIs specify what these arrays are called.

The formats are inconsistent about including the value of the gravitational constant G, so it can be passed as an argument when loading a model.

For each format, tomso returns an object with convenient properties. e.g. although the sound speed isn’t a field in any of the standard formats, using the cs property will compute it. For example, here’s Fig. (7.30) of Aerts, Christensen-Dalsgaard & Kurtz (2010), in which we also use the acoustic depth through the property tau:

import numpy as np
import matplotlib.pyplot as pl
from tomso import fgong

S = fgong.load_fgong('../tests/data/modelS.fgong', G=6.67232e-8)
pl.plot(S.tau, np.gradient(S.cs, S.tau)/1e4)
pl.xlabel("τ (sec)")
pl.ylabel("dc/dτ (10⁴ cm/s²)")
pl.axis([100., 3000., 0., 2.5])

Some properties can be modified but if you want to start writing files from scratch, you should make sure you understand the formats and consider modifying the underlying data arrays directly.