THE IMPORTANCE OF REALISTIC STARTING MODELS FOR HYDRODYNAMIC SIMULATIONS OF STELLAR COLLISIONS

We demonstrate the necessity of using realistic stellar models taken f rom stellar evolution codes, as opposed to polytropes, for starting mo dels in smoothed particle hydrodynamics calculations of collisions bet ween main-sequence stars. Evolved stars have mean molecular weight gra dients, which affect their entropy profiles and therefore affect how t hey react during a collision. The structure of stellar collision produ cts of polytrope parent stars is significantly different from that of collision products of realistic parent models. These differences stron gly affect the future evolution of the collision products, particularl y products of collisions between unequal mass stars which have undergo ne significant chemical evolution. The use of polytropes as parent sta r models is likely to result in qualitatively mistaken results for the structure of the collision product.