Blue stragglers as stellar collision products: the angular momentum question

Abstract

We investigate the structure and evolution of blue straggler stars, which were formed from direct stellar collisions between main-sequence stars in globular clusters. In particular, we look at the rotational evolution of the products of off-axis collisions. As found in previous work, such blue stragglers initially have too high an angular momentum to contract down to the main sequence. We consider angular momentum loss through either disc locking or locking to an outflowing wind, and we show that both methods allow the merged object to shed sufficient angular momentum to contract down to the main sequence.