22 - Rotation in core collapse progenitors: single and binary stars

Summary

Abstract

Current massive single star evolution models with rotation, especially when magnetic fields are included, appear to get close in reproducing the spin rates of young neutron stars. This, however, excludes them as progenitors of gamma-ray bursts within the collapsar model. Close binary evolution models with rotation, on the other hand, suggest that the mass receiving star is spun-up appreciably and may retain enough angular momentum in its core until collapse, while the mass donor is spun-down to produce core rotation rates below those of single stars.

Introduction

The evolution of a single star can be strongly influenced by its rotation (e.g., Heger & Langer 2000; Meynet & Maeder 2000), and evolutionary models of rotating stars are now available for many masses and metallicities. While the treatment of the rotational processes in these models is not yet in a final stage (e.g., magnetic dynamo processes are just about to be included; Heger et al. 2003), they provide first ideas of what rotation can really do to a star.

Effects of rotation, as important as they are in single stars, can be much stronger in the components of close binary systems: Estimates of the angular momentum gain of the accreting star in mass transferring binaries show that critical rotation may be reached quickly (Packet 1981; Langer et al. 2000). Therefore, we need binary evolution models which include a detailed treatment of rotation in the stellar interior, as in recent single star models.