Effect of low-temperature opacities on stellar evolution

Abstract

Stellar evolution is studied through computational models of stars since any perceived change in the stars can take thousands if not millions of years. One of the physical quantities that defines the evolution of a star is known as the opacity. Opacity of a material determines how much electromagnetic radiation passes through the material. Scattering and absorption processes in the radiative region of the star determine the opacity of that region and regulate radiative energy flow in the star. The mean opacity which is averaged over all wavelengths depends on the temperature, density, and the composition of the material in the star. Currently, tables of mean opacities are used in stellar modeling. These opacities are given as functions of temperature and density and the tables are made for several compositions which changes with evolution of the star. At low temperatures, formation of molecules and dust grains can affect the mean opacity. In this study, low-temperature opacity tables are made with opacity codes ATOP and PHOENIX and stellar models produced with these opacity tables with the stellar evolution code MESA are compared. In addition, the effect of initial elemental abundance sets and molecular data sources on stellar evolution is studied. Finally, the impact of low-temperature opacities on the pace of stellar evolution is analyzed with stellar isochrones. The results show that there is negligible difference between stellar models produced with ATOP and PHOENIX and with different molecular data sources. However, changing the initial elemental abundance set generated significant changes in stellar evolution.