Analytic Polytropic Models

Setting the model_type option of the &model namelist group to one of 'ANAPOLY_0', 'ANAPOLY_1', or 'ANAPOLY_5' tells the frontend to create an analytic polytropic stellar model with the indicated polytropic index (e.g., ANAPOLY_1 has an index \(\npoly=1\)). Because the structure of these model can be computed analytically, there is no need to read from an external file. The 'ANAPOLY_5_1' option is a special case, constructed by matching an inner \(\npoly=5\) region to an outer \(\npoly=1\) region; the location of the matching point is set by the x_match option (see Eggleton et al., 1998 for details).

The Gamma_1 option controls the first adiabatic index of the model, while the n, s and grid_type options control the model grid. See the Model Namelist Group section for further information.

It’s possible to create truncated polytropic models, with a finite surface pressure and density, by setting theta_s to a value other than zero (this option represents the desired surface value of the polytropic dependent variable \(\theta\)). A non-zero theta_s is required when using 'ANAPOLY_5' models, because the star would otherwise have an infinite radius.