Hybrid solar model

Abstract

A solar evolution code is written to solve the stellar structure equations and evolve the Sun from the zero-age main sequence (ZAMS) model to the present age of the Sun. Accuracy is the most important factor in constructing a stellar evolution code. Therefore, we use double precision in constructing our code using FORTRAN. We build a hybrid solar model based on two numerical methods, which are the shooting method (or fitting method) and the collocation method, using the most updated physics, for example the updated OPAL opacity (1996) and the updated compositions mixture of Grevesse & Sauval (1998). The shooting method is used to solve the stellar structure equations while collocation method is used to further increase the accuracy of the integrations. The atmospheric outer boundary condition is simplified to limit the free parameters so that the numerical accuracy of our approach can be inferred accurately. With the use of collocation method, we can achieve accuracy up to 10-10 in the central region of the Sun. Considering the upper bound error, our hybrid model is estimated to have accuracy between 10-6 and 10-4.