Modification of the radiation transfer equations to take into account NLTE effects in the simulations of supernova light curves by the radiation hydrodynamic code STELLA

The observed supernova broadband light curves serve as an extensive source of information about the physics of presupernovae and about the processes taking place during supernova outbursts. Their modeling requires complex calculations using radiation-hydrodynamic codes. The paper proposes to modify the STELLA radiation-hydrodynamic code to take into account NLTE (local thermodynamic equilibrium) effects in the calculation of supernova light curves. The paper provides a theoretical justification for the need to take into account the effects of NLTE when calculating the level number densities of multicharged plasma in a supernova envelope. A modification of equations of time-dependent radiation transfer and the equation of gas energy to take into account the NLTE effects is described. Various methods of mean opacity coefficients in the expanding envelope of supernovae are analyzed.