Inlists for MESA are composed of five main sections labeled
&star_job section contains instructions about which MESA modules should be used, while the
&controls section is where the star module options are specified. The
&eos sections are where you specify controls for the opacity and the equation of state respectively.
&pgstar section contains the commands for creating pgstar plots.
The main modules of MESA (other than star) are the Equation of state (eos), the Opacities (kap), the Atmospheres (atm), the nuclear reactions. In this section of the inlist, you’ll have to make choices for which atmosphere and nuclear reactions network you want to use, as well as which nuclear reactions rates you want to use. You will also specify here some information about your starting model, and about the output of the evolution. Here we describe only some of the most commonly used controls. For a complete list of available controls see star_job.
To start an evolution you can either create a pre main sequence model and start from there (case 1) or you can start from a previously calculated model (case 2). In the latter case, it is highly recommended to start from a model which was calculated with the same MESA version as the one used for the subsequent evolution.
create_pre_main_sequence_model = .true. load_saved_model = .false.
create_pre_main_sequence_model = .false. load_saved_model = .true. load_model_filename = 'start.mod'
There are a number of controls to specify what we want as MESA outputs.
The history file contains global information about the star at some timesteps. The profile files contain information about the interior profiles in the stellar model at a given time. The defaults for these files are located in
If you want output different from the defaults, copy those files in your working directory, rename them (here we use
my_profile_columns.list) , and customize them to your liking. If you include the following lines in your inlist, MESA will use the files sitting in your working directory rather than the default files.
history_columns_file = 'my_history_columns.list' profile_columns_file = 'my_profile_columns.list'
You may want to save the final model of your evolution. In that case you have to tell MESA to do so (default is
save_model_when_terminate=.false.) and specify the name of the last model.
save_model_when_terminate = .true. save_model_filename = 'final.mod'
There are several ways to specify the initial composition. (to be filled in).
You can also use pre-defined chemical compositions based on published data. These are set using the control
By default, the initial composition in MESA is
initial_zfracs = 3 which corresponds to the GS98 metal fraction. There are 8 possible predefined choices for this control in MESA.
If you want for example to use the more recent available solar composition given in AGSS09 , you need to set
initial_zfracs = 6.
Since it is very important to use the opacity tables which are built using the solar composition used, we also have to set the
kappa_file_prefix to the 2009 solar composition (the default table corresponds to the gs98 composition).
initial_zfracs = 6 kappa_file_prefix = 'a09'
Choice of network of nuclear reactions. This network should be chosen according to the physics to be studied. Choosing a very comprehensive set of nuclear reactions when studying main sequence evolution is not necessary and will slow down the computation considerably. It would however be essential when studying advanced burning stages of evolution. The description of the available nuclear reactions networks in MESA is given in the README file in
$MESA_DIR/data/net_data. The default reactions network used by MESA is
For example when evolving a stellar model on the horizontal branch (helium burning) this net is insufficient. One possibility is to use the nuclear reactions network called
pp_and_cno_extras.net, which provides a more complete coverage for hydrogen and helium burning.
change_initial_net = .true. new_net_name = 'pp_and_cno_extras.net'
The energy equation can be written in the dLdm or the dedt form in MESA (see MESAV). As explained in MESAV, using the dedt form leads to much better energy conservation. The dLdm form is currently the default in MESA. If the dEdt form is preferred it has to be specified in the inlist.
energy_eqn_option = 'dedt'
The main stellar parameters to specify are its initial mass M, metallicity Z, and helium fraction Y. If only M and Z are specified,the helium content is by default Y=0.24 + 2Z.
initial_mass = 2.0 initial_z = 2d-2
When to stop¶
Type2 opacities should be used for extra C/O during and after He burning. To use Type2 opacities one needs to specify a base metallicity, Zbase, which gives the metal abundances previous to any CO enhancement. In regions where central hydrogen is above a given threshold, or the metallicity is not significantly higher than Zbase, Type1 tables are used instead, with blending regions to smoothly transition from one to the other. The reason is that Type1 tables cover a wider range of X and have a higher resolution in Z for each X. For more info, refer to the
If the evolution includes helium burning, type2 opacities should be used.
use_Type2_opacities = .true. Zbase = 2d-2
Convection and Convective boundaries¶
Convection in MESA is treated using the MLT theory of convection, and provides different formalisms. By default, MESA uses the Cox&Giuli 1968 formalism.
If you want to use another formalism, for example the Henyey theory of convection it can be specified using the
MLT_option control. Several parameters can be specified for this option. The main one is the mixing length parameter. Note that the default value for this parameter in MESA is
mixing_length_alpha=2. This value does not come from any calibration.
MLT_option = 'Henyey' mixing_length_alpha = 1.8d0
There are two possible criteria that can be used to determine the position of the convective boundaries: the Schwarzchild and Ledoux criteria. By default MESA uses the Schwarzchild criterion. If determined correctly, the position of the convective boundaries should not depend on which criterion is used. But using the Schwarzchild or the Ledoux criterion can lead to different abundance profiles outside the convective region. There are extensive discussions about this topic in the MESAIV and MESAV papers. Two new algorithms have been introduced in MESA, called Predictive mixing (described in MESAIV )and Convective PreMixing, described in MESAV). By default, none of these are used in MESA, which can lead to very incorrectly determined convective boundaries, with important consequences on the evolution of the stellar model. It is therefore highly recommended to use one of these algorithms.
If using Convective premixing, there is no additional parameter to specify.
use_Ledoux_criterion = .true. do_conv_premix = .true.
If using Predictive mixing, there are additional controls. They are described in MESAIV .
predictive_mix(1) = .true. predictive_zone_type(1) = 'any' predictive_zone_loc(1) = 'core' predictive_bdy_loc(1) = 'any' predictive_superad_thresh(1) = 0.005 predictive_mix(2) = .true. predictive_zone_type(2) = 'any' predictive_zone_loc(2) = 'surf' predictive_bdy_loc(2) = 'any' predictive_superad_thresh(2) = 0.001