Evolution of Stellar Collision Products in Globular Clusters. II. Off‐Axis Collisions

We continue our exploration of collisionally merged stars in the bluestraggler region of the color-magnitude diagram. We report the results of newSPH calculations of parabolic collisions between two main-sequence stars, withthe initial structure and composition profiles of the parent stars having beendetermined from stellar evolution calculations. Parallelization of the SPH codehas permitted much higher numerical resolution of the hydrodynamics. We alsopresent evolutionary tracks for the resulting collision products, which emergeas rapidly rotating blue stragglers. The rotating collision products arebrighter, bluer and remain on the main sequence longer than their non-rotatingcounterparts. In addition, they retain their rapid rotation rates throughouttheir main sequence lifetime. Rotationally-induced mixing strongly affects theevolution of the collision products, although it is not sufficient to mix theentire star. We discuss the implications of these results for studies of bluestraggler populations in clusters. This work shows that off-axis collisionproducts cannot become blue stragglers unless they lose a large fraction oftheir initial angular momentum. The mechanism for this loss is not apparent,although some possibilities are discussed.Comment: 25 pages incl. 9 figures (one in colour). Submitted to Ap