# Atmosphere Structure Building¶

MESA’s atm module is primarily used to evaluate the $$T_{\rm surf}$$ and $$P_{\rm surf}$$ values for the boundary conditions. However, when writing output files for pulsation codes (using the save_pulse_data... controls), it is sometimes desirable to append the (spatial) atmosphere structure data to the interior structure data; that way, the extension of modes into the stellar atmosphere can naturally be modeled by the pulsation code.

To append atmosphere structure data in this way, set the add_atmosphere_to_pulse_data control to .true.. A couple of caveats apply:

• This capability is only available when atm_option has the values 'T_tau' or 'Paczynski_grey'. For other values (e.g., 'table'), there are insufficient data to determine what the spatial structure of the atmosphere should be.
• It’s important to realize that calculation of atmosphere structure data has NO effect on the evolution of the star, OR on MESA’s standard profile, history and photo outputs. Only the pulsation output files are affected.

When building atmosphere structure data, a number of controls influence the calculation, as follows:

 Control Meaning atm_build_errtol Error tolerance for integrating the $$r(\tau)$$ [and possibly also $$T(\tau)$$] equations atm_build_dlogtau Maximum logarithmic spacing $$\Delta\log_{10}(\tau)$$ for atmosphere structure data atm_build_tau_outer Outermost optical depth $$\tau_{\rm outer}$$ for atmosphere structure data. The structure will extend from $$\tau_{\rm surf}$$ to this value, and contain approximately $$[\log_{10}(\tau_{\rm surf}) - \log_{10}(\tau_{\rm outer})]/\Delta\log_{10}(\tau)$$ points