The Importance of Realistic Starting Models for Hydrodynamic Simulations of Stellar Collisions

We demonstrate the necessity of using realistic stellar models taken from stellar evolution codes, as opposed to polytropes, for starting models in smoothed particle hydrodynamics calculations of collisions between main-sequence stars. Evolved stars have mean molecular weight gradients, which affect their entropy profiles and therefore affect how they react during a collision. The structure of stellar collision products of polytrope parent stars is significantly different from that of collision products of realistic parent models. These differences strongly affect the future evolution of the collision products, particularly products of collisions between unequal mass stars which have undergone significant chemical evolution. The use of polytropes as parent star models is likely to result in qualitatively mistaken results for the structure of the collision product.