Evolution of stellar collision products in globular clusters

We explore the evolution of collisionally merged stars in the blue straggler region of the H-R diagram. The starting models for our stellar evolution calculations are the results of the smoothed particle hydro-dynamics (SPH) simulations of parabolic collisions between main-sequence stars performed by Lom-bardi, Rasio, & Shapiro. Since SPH and stellar evolution codes employ di†erent and often contradictory approximations, it is necessary to treat the evolution of these products carefully. The mixture and dis-parity of the relevant timescales (hydrodynamic, thermal relaxation, and nuclear burning) and of the important physical assumptions between the codes makes the combined analysis of the problem chal-lenging, especially during the initial thermal relaxation of the star. In particular, the treatment of convec-tion is important and semiconvection must be modeled in some detail. The products of seven head-on collisions are evolved through their initial thermal relaxation and then through the main-sequence phase to the base of the giant branch. Their evolutionary tracks are present-ed. In contrast to what was assumed in previous work, these collision products do not develop substan-tial convective regions during their thermal relaxation and therefore are not mixed signiÐcantly after the collision