  We explore the evolution of collisionally merged stars in the blue straggler
region of the HR diagram. The starting models for our stellar evolution
calculations are the results of the smoothed particle hydrodynamics (SPH)
simulations of parabolic collisions between main sequence stars performed by
Lombardi, Rasio and Shapiro (1996). Since SPH and stellar evolution codes
employ different and often contradictory approximations, it is necessary to
treat the evolution of these products carefully. The mixture and disparity 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 challenging, especially during the initial thermal
relaxation of the star. In particular, the treatment of convection 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 presented. In contrast to the
assumptions in previous work, these collision products do not develop
substantial convective regions during their thermal relaxation, and therefore
are not mixed significantly after the collision.
